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Physics Astrophysics Cosmology and Nongalactic Astrophysics

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Monday 24 August

Cosmology and Nongalactic Astrophysics

A New Probe of Dark Matter Subhalos: Stellar Aberration with TESS

Matthias Daniel, Xiao Xue, Kris Pardo et al. (+1 more)

Small-scale dark matter (DM) structure encodes key information about the particle nature of DM and therefore provides a sensitive test of competing models. Yet, it remains hidden from electromagnetic surveys and is instead inferred through its gravitational effects. Stellar aberration, the apparent shift in a light source's position induced by the observer's motion, offers a largely unexplored channel to access such signatures. DM subhalos can perturb the observer's motion, imprinting characteristic, spatially correlated shifts in stellar positions across the sky. We show that the Transiting Exoplanet Survey Satellite (TESS), with its long temporal baseline, wide sky coverage, and high-cadence observations, is well suited to search for these aberration signals. We derive Fisher-matrix-based sensitivity estimates for constant observer accelerations, forecasting a sensitivity down to $6.3\times 10^{-9}\,\mathrm{m/s^2}$ from the combined sample of TESS stars with magnitude $\mathrm{Tmag}\leq 10$. This sensitivity allows TESS to probe concentrated DM subhalos over a broad parameter space, from $\gtrsim 10^{-6}\,\mathrm{M_{\odot}}$ at AU-scale distances to $\gtrsim 10^{7}\,\mathrm{M_{\odot}}$ at $\mathcal{O}(10\,\mathrm{pc})$. TESS's sector-based observing strategy further provides intrinsic temporal resolution of potential DM-induced aberration signals. Moreover, we briefly discuss challenges for future data analysis, including the modeling of instrumental systematics and stellar astrometric foregrounds, such as parallax and proper motion. Our results establish stellar aberration as a novel probe of DM substructure, paving the way for dedicated searches in TESS and next-generation wide-field surveys.
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All authors Matthias Daniel, Xiao Xue, Kris Pardo, Laura Sagunski

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Topics in the phenomenology of axions: the cases of cosmic strings and superradiance

Antonios Kyriazis

Originally proposed as a solution to the strong CP problem and later understood to be a good dark matter candidates, axions have appeared in a variety of beyond-the-standard-model theories and are imbued with rich phenomelogical consequences. In this dissertation, we will examine two of these consequences: the emission of axions from cosmic strings and the superradiant mechanism in black hole physics. The spontaneous symmetry breaking of a global symmetry in the early universe can give rise to a network of cosmic strings, which emit ultra light, axion-like particles that can contribute to the dark matter density. We will discuss how the associated density fluctuations of these particles can be computed from first principles by treating them as a collection of plane waves. We will then calculate the density power spectrum and compare it to well-established cosmological observables, as well as to observables from future surveys, to derive constraints on the mass of the particles and the symmetry breaking scale. These light axion-like particles can also form a gravitational atom around a spinning black hole through the superradiance process. Considering the black hole to be part of a binary system, the tidal potential of the companion periodically perturbs the gravitational atom such that an atomic transition occurs between two of its energy states. Gravitational waves are emitted by the cloud during this transition. We will derive the analytical formulae of both the strain waveform and frequency spectrum of the signal and identify the systems that would be the most promising for detecting it in future, space-based gravitational wave observatories.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Defining higher memory signals and forecasting their observation prospects for binary-black-hole mergers with next-generation gravitational-wave detectors

Siddhant Siddhant, Alexander M. Grant and David A. Nichols

In asymptotically flat spacetimes far from an isolated source, gravitational waves (GWs) undergo nonlinear interactions with themselves and with the parts of the spacetime curvature related to the time-dependent four-momentum and angular momentum of the spacetime. These spacetime nonlinearities produce distinctive offsets in the GW strain and its time integrals, which have been referred to as the displacement memory effect for the strain and “higher” GW memory effects for the integrals of the strain. There are existing data analysis pipelines that search for evidence for the displacement memory effect in the population of binary-black-hole mergers observed by current GW detectors (though conclusive evidence for the effect has not yet been found). The first set of higher memory effects include the spin and center-of-mass effects (collectively, “drift” memory), and the second is the “ballistic” memory effect. Prior work has shown that next-generation, ground-based GW detectors could find evidence for the spin memory effect in the large population of binary black holes that these detectors will be capable of observing. In this paper, we investigate how well a detector network of two Cosmic Explorer detectors can measure the displacement through ballistic memory signals. We first formulate what are appropriate notions of time-dependent GW signals associated with these memory effects. With these definitions of displacement and higher memory signals, we find that the Cosmic Explorer network is capable of detecting the displacement memory from tens of individual mergers per year and capable of finding evidence for the spin and center-of-mass memory effects in a population of mergers after a roughly one-year observation run at design sensitivity. [Abstract abridged]
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Cosmology and Nongalactic Astrophysics

Beyond $w_0-w_a$ and Phantom Crossing: Testing Models of Coupled Dark Sector

Kaynan R. de O. Pompeu, João Rebouças and Rogerio Rosenfeld

The combination of cosmic microwave background (CMB) measurements with distance measurements from baryon acoustic oscillations (BAO) and type Ia supernovae (SNIa) suggests that dark energy is dynamical, with an equation of state crossing the phantom divide at low redshifts. This feature can not be described within canonically normalized, minimally coupled, self-interacting scalar field models. We investigate the possibility of achieving phantom crossing by introducing an interaction in the dark sector such that the dark matter particle mass is dependent on the dark energy field $\phi$ as $m \propto \phi^\alpha$. We consider a self-interacting potential of the inverse power-law form $V \propto \phi^{-\beta}$. We implement this model both at the background and perturbative levels in a Boltzmann solver and use a bayesian framework to constrain its parameters using using CMB, BAO and SNIa data. We find best-fits that have similar goodness-of-fits as the commonly used phenomenological $w_0-w_a$ parameterization, providing a more fundamental understanding of the dark sector.
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Cosmology and Nongalactic Astrophysics · Cross-listed from nucl-th

Deuterium Production in an Effective Field Theory Constructed from On-Shell Amplitudes

Tim M.P. Tait

We compute the deuterium-production reaction $n+p \to d+\gamma$ in an effective field theory whose degrees of freedom are the nuclear states themselves: the amplitude is assembled from on-shell three-point vertices, glued across its factorization channels, and completed by the contact terms consistent with the symmetries. The deuteron enters through the $d$-$n$-$p$ vertex, normalized to the measured asymptotic normalization coefficient. Rescattering of the nucleon pair is resummed dispersively, leaving two short-distance constants, an isovector magnetic and an electric dipole contact interaction. A joint Bayesian fit to the thermal capture measurements and the SLEGS photodisintegration data finds both of natural size and determines the thermonuclear rate to 0.22-0.24% across the nucleosynthesis window, including systematics spanning the defensible treatments of the SLEGS data and of the $P$-wave rescattering. Truncating the expansion is bounded separately at 0.12%, of which the next order of contact terms – degenerate with the two fitted constants – supplies 0.03%, for a total theory uncertainty of 0.25-0.27%. Propagated through a BBN network, the rate shifts the predicted primordial deuterium by -0.06% and cuts this reaction's contribution to the D/H uncertainty from 0.089% to 0.050%, retiring it from the primordial D/H error budget for practical purposes.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

Color-Kinematics Duality and the Double Copy in Curved Spacetimes

Mariana Carrillo González

The double copy relates gravitational data to gauge-theory data, most sharply through color-kinematics duality for flat-space scattering amplitudes. This review surveys the extent to which this idea can be formulated beyond asymptotically flat backgrounds. After recalling the flat-space ingredients needed for comparison, we describe curved-space constructions for boundary correlators and scattering observables in AdS, dS, and other non-trivial backgrounds. We then review classical and field-level maps, including Kerr–Schild, Weyl, Cotton, twistor, and convolutional double copies. A separate part is devoted to self-dual sectors. Throughout, we emphasize both the common structures that survive from flat space and the obstructions introduced by curvature.
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Cosmology and Nongalactic Astrophysics

Exact Equivalence of the Observed Redshift and the Pulsar Timing Modulation in the Infinitesimal-Pulse Limit

Matteo Magi and Jaiyul Yoo

The pulsar timing arrays (PTA) collect the times of arrival of radio signals from the millisecond pulsars, and gravitational waves can modulate their arrival times. Although the PTA observable involves successive radio pulses propagating along different light paths, its standard theoretical description at linear order in perturbations is equivalent to the Sachs-Wolfe formula for the observed redshift, which describes the fractional change in photon frequency along a single geodesic. While this equivalence is well known at linear order, its validity beyond first order has not been systematically addressed in the PTA literature. Here we show that, in the limit of vanishing proper-time separation between successive emission events, the timing modulation is exactly equal to the observed redshift, without expanding the spacetime geometry. For a finite emission interval, we derive the exact relation between the timing modulation and the observed redshift, and show that their difference is controlled by the ratio between the emission interval and the characteristic timescale over which the observed redshift varies.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

When the HL-LHC is blind, LISA is deaf (but not vice versa): 2HDM collider-cosmology synergies

Stefano Moretti, André Pousette and Carlo Tasillo

Extensions of the Standard Model scalar sector can render the electroweak phase transition first-order and thereby provide the departure from thermal equilibrium required for electroweak baryogenesis, while at the same time sourcing a stochastic gravitational wave (GW) background in the milli-Hertz range. In this work, we investigate electroweak phase transitions in the CP-conserving type-I two-Higgs-doublet model (2HDM), focusing on the interplay between collider constraints at the HL-LHC and the projected sensitivity of LISA. We compute the expected GW background due to strong first-order electroweak phase transitions and perform extensive Monte Carlo scans over the collider-viable model parameter space. We find that GW signals within reach of LISA arise almost exclusively in regions of parameter space that necessarily predict observable deviations at the HL-LHC, in particular through the $H \to ZZ$ decay channel of the heavy CP-even and neutral Higgs state with $m_H \simeq 180\text{--}250 \, \text{GeV}$. Our results highlight the decisive complementarity between collider and GW probes and show that the largest parts of the 2HDM parameter space relevant for phase transition signals at LISA can already be tested by HL-LHC. A possible future discovery of 2HDM states at the HL-LHC, however, would not allow conclusive statements about LISA being able to find a GW background due to the amount of parameter tuning required for an observable GW signal. In order to evaluate possible caveats of this statement we study the theoretical uncertainties related to the GW predictions in a two-fold approach using both state-of-the-art tools, BSMPT and TransitionListener, and also allow for model realizations in which the electroweak symmetry is not restored in the high-temperature limit, which are the ones combining the loudest GW signals with the weakest collider coverage.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

Wilsonian Cosmology: de Sitter (in)Stability

Jean Alexandre, Lucien Heurtier and Silvia Pla

We develop a (Wilsonian) functional-renormalisation-group framework for scalar cosmology in which quantum fluctuations of a scalar field are coarse-grained on cosmological spacelike hypersurfaces. Integrating out quantum fluctuations with wavelengths smaller than the Hubble radius $H(t)^{-1}$, we obtain an effective scalar potential $U(\phi(t),H(t))$ that evolves in time. We derive a non-perturbative flow equation for this potential, together with the coupled set of (modified) Friedmann equations. We then apply this formalism to the simplest possible case of a de Sitter vacuum when the scalar field is at rest, in two situations which satisfy exactly our flow equation: $(i)$ A flat potential, for which we find that the only pure de Sitter solution is unstable and corresponds to a saddle point. $(ii)$ A quadratic potential with curvature $m^2>0$, for which we find that the presence of the mass term stabilises the system. The latter case leads to a de Sitter attractor either at the Hubble scale when the mass is larger than the Hubble scale at initial time, or by introducing a new attractor located at $H=m$ in the case the mass is smaller, which may be particularly relevant to the phenomenological study of dark energy and inflation theories.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

More Numerous and Bluer: Companions of the Brightest Little Red Dots Differ from Control Galaxies at $>3\sigma$, Hinting at Synchronized Black Hole Seed Formation

Fabio Pacucci and C. Megan Urry

The Little Red Dots (LRDs) are compact, red sources at $4 \lesssim z \lesssim 9$, likely powered by accreting massive black holes. Multiple studies have detected blue companions in their vicinity: we compare $253$ LRDs, uniformly selected across several JWST deep fields, against $>7000$ matched controls in the same mosaics. We find that $27.7\%$ of the brightest LRD quartile (in F444W) hosts a blue ($\beta<-1$) companion at $0.5-2$ kpc, versus $11.6\%$ of redshift-matched controls: a $\times 2.39$ excess, significant at $3.3\sigma$. Against controls additionally matched in brightness and compactness, the excess ratio is similar ($\times 2.17$), although constrained only at $1.4\sigma$ by the small size of that control pool. This phenomenon is limited to the brightest LRDs, as the full LRD sample pairs at a rate indistinguishable from controls. Moreover, the excess is confined to the close-pair window ($< 2$ kpc), outside which LRD environments are ordinary. Their companions are overwhelmingly ($92\%$) blue and significantly bluer than those of controls ($\beta\approx-2.32$ versus $-1.92$), rejecting a common parent distribution at $3.4\sigma$. The signal is thus directional in brightness, separation, and companion color, as expected for synchronized-pair seed formation. Therefore, we conclude that the association between the brightest LRDs and their close blue companions is physical, i.e., the two phenomena are causally connected: either one drives the other, or both emerge from the same synchronized formation event. A natural explanation is that the radiation from these young, star-forming neighbors enabled the direct collapse of the massive black holes powering the LRDs themselves.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM

Strong Lensing Cosmology with Population-level Calibrated Neural Ratio Estimation

Sreevani Jarugula, Brian D. Nord, Aleksandra Ćiprijanović et al. (+1 more)

Strong gravitational lensing contains key information about cosmic acceleration. Modern and next-generation galaxy imaging surveys are expected to provide high-quality data on $\mathcal{O}(10^5)$ galaxy-galaxy lensing systems. The plethora and complexity of the data are likely to present computational challenges for parameter inference methods for fitting high-dimensional likelihoods, which are often analytically intractable. Neural Ratio Estimation (NRE) efficiently computes individual likelihood ratios that can be combined into population-level posteriors. We use simulations to study the capacity of NRE to jointly predict the dark energy equation-of-state parameter $w$ and the total matter density $\Omega_{m}$ from lensing images and companion spectroscopic information. We also introduce a post hoc posterior coverage calibration procedure that mitigates the model overconfidence that is typically found in neural density estimation applications. Our experiments show that the errors on both parameters decrease with increasing inference population sizes. In particular, for 100 lenses in a standard $\Lambda$CDM Universe, our calibrated NRE model achieves median fractional uncertainty of $22.8\%$ in $w$ and $2.9\%$ in $\Omega_{m}$. This proof of concept demonstrates a potentially scalable approach for efficient cosmological parameter inference with large populations of galaxy-scale lenses observed in future surveys.
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All authors Sreevani Jarugula, Brian D. Nord, Aleksandra Ćiprijanović, Shubhendu Trivedi

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

The Road to Normalcy: Environment-Driven Evolutionary Pathways for Primordial Black Holes

Saiyang Zhang, Junehyoung Jeon, Boyuan Liu et al. (+2 more)

We investigate how cosmological environment regulates the evolution of primordial black hole (PBH) seeds in the early universe using a suite of hydrodynamical simulations. Unlike traditional seeding channels, PBHs provide early BH seeds without the need of special conditions for gas collapse/fragmentation that favor overdense regions, thus covering diverse large-scale environments. We find that PBHs follow distinct evolutionary pathways depending on the gas supply and halo assembly history. In underdense regions, limited inflow suppresses both accretion and star formation, producing faint, metal-poor systems, while in overdense environments, sustained gas inflow drives rapid BH growth and the formation of compact, centrally concentrated stellar components. These differences lead to large variations in BH-to-stellar mass ratio, metallicity, and morphology, collectively bracketing a range of possible evolutionary pathways for PBH-seeded systems. We show that compact, BH-dominated sources resembling recently observed Little Red Dots naturally arise as one phase within these evolutionary pathways before evolving into more extended galaxy–AGN systems. Our results suggest that both the initial seed properties and cosmological environment jointly shape early BH–galaxy co-evolution, while subsequent environmental regulation can erase the memory of the initial seeding channel.
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All authors Saiyang Zhang, Junehyoung Jeon, Boyuan Liu, Volker Bromm, Priyamvada Natarajan

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Updated Upper Limits on the Isotropic Gravitational-Wave Background from LIGO, Virgo, and KAGRA Data through April 2025

The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration: A. G. Abac et al. (+1804 more)

We report results from a search for an isotropic stochastic gravitational-wave background using data collected by the LIGO–Virgo–KAGRA Collaboration. The analysis uses data from the first observing run through April 1, 2025, during the fourth observing run. New frequency-domain cuts are implemented to address a class of non-stationary spectral noise features that were not effectively identified and mitigated by existing data-quality checks in past analyses. Consequently, previously analyzed data from the fourth observing run are re-processed with the updated cuts. We find no evidence for a stochastic background signal and place upper limits on the gravitational-wave energy density. In particular, for a background following a power law with spectral index 2/3 as predicted by inspiralling compact binaries, we find $\Omega_\mathrm{GW}(25\,\mathrm{Hz}) \leq 2.0 \times 10^{-9}$, while scale-invariant backgrounds are constrained to $\Omega_\mathrm{GW}(25\,\mathrm{Hz}) \leq 2.8 \times 10^{-9}$, both at the 95% credible level for a log-uniform prior on $\Omega_\mathrm{GW}$. Relative to the constraints from previous data recomputed with the new frequency-domain cuts, these limits improve by a factor of 1.4. We also update bounds on alternative gravity scenarios predicting non-standard polarization modes, and we verify that correlated magnetic noise sources remain below the sensitivity of this search. Combining these observational constraints with population models of compact binary coalescences informed by the latest gravitational-wave transient catalog, GWTC-5.0, we predict the amplitude of the compact binary background to be $\Omega_\mathrm{CBC}(25\,\mathrm{Hz}) = 6.3^{+5.0}_{-2.2} \times 10^{-10}$ at the 90% credible level.
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All authors The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration: A. G. Abac, A. Abe, I. Abouelfettouh, F. Acernese, K. Ackley, A. Adam, C. Adamcewicz, S. Adhicary, D. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I.-L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu, L. Albers, W. Ali, S. Al-Kershi, C. Allene, A. Allocca, S. Al-Shammari, J. A. Alvarez, S. Alvarez-Lopez, W. Amar, O. Amarasinghe, A. Amato, F. Amicucci, C. Amra, A. B. Anand, C. Anand, A. Ananyeva, S. B. Anderson, W. G. Anderson, M. Andia, M. Ando, F. Andrade-Oliveira, M. Andrés-Carcasona, J. L. Andrey, T. Andrić, J. Anglin, J. Anna, J. M. Antelis, S. Antier, T. Aoki, M. Aoumi, E. Z. Appavuravther, E. A. Appelt, S. Appert, S. K. Apple, K. Arai, A. Araya, M. C. Araya, F. Arciprete, J. S. Areeda, N. Aritomi, F. Armato, S. Armstrong, N. Arnaud, M. Arogeti, S. M. Aronson, G. Ashton, Y. Aso, L. Asprea, M. Assiduo, S. Assis de Souza Melo, S. M. Aston, P. Astone, P. S. Aswathi, F. Attadio, F. Aubin, K. AultONeal, G. Avallone, N. Avdeev, E. A. Avila, S. Babak, C. Badger, S. Bae, S. Bagnasco, S. Baimukhametova, L. Baiotti, T. Baka, K. A. Baker, T. Baker, G. Balbi, G. Baldi, N. Baldicchi, M. Ball, G. Ballardin, M. Ballelli, S. W. Ballmer, S. Banagiri, B. Banerjee, D. Bankar, T. M. Baptiste, P. Baral, M. Baratti, J. C. Barayoga, K. Baric, B. C. Barish, D. Barker, N. Barman, F. Barone, B. Barr, M. Barrios, L. Barsotti, M. Barsuglia, D. Barta, M. A. Barton, I. Bartos, A. Basalaev, R. Bassiri, A. Basti, M. Bawaj, J. C. Bayley, A. C. Baylor, P. A. Baynard II, M. Bazzan, V. M. Bedakihale, F. Beirnaert, M. Bejger, A. S. Bell, C. Bellani, D. S. Bellie, D. Beltran-Martinez, E. Benedetti, W. Benoit, I. Bentara, M. Ben Yaala, S. Bera, F. Bergamin, B. K. Berger, M. Beroiz, I. Berry, D. Bersanetti, T. Bertheas, A. Bertolini, J. Betzwieser, D. Beveridge, N. Bevins, J. Bezerra-Sobrinho, R. Bhandare, R. Bhatt, A. Bhattacharjee, D. Bhattacharjee, S. Bhattacharyya, S. Bhaumik, V. Biancalana, F. Bianchi, I. A. Bilenko, M. Bilicki, G. Billingsley, A. Binetti, S. Bini, S. Biot, O. Birnholtz, S. Biscoveanu, A. Bisht, M. Bitossi, M.-A. Bizouard, S. Blaber, J. K. Blackburn, L. A. Blagg, C. D. Blair, D. G. Blair, M. Bloch, N. Bode, N. Boettner, P. Bogdan, G. Boileau, M. Boldrini, G. N. Bolingbroke, L. D. Bonavena, V. A. Bonhomme, E. Bonilla, M. S. Bonilla, A. Bonino, R. Bonnand, A. Borchers, N. Borghi, V. Boschi, S. Bose, V. Bossilkov, Y. Bothra, A. Boudon, T. D. Boybeyi, M. Boyle, A. Bozzi, C. Bradaschia, M. J. Brady, P. R. Brady, A. Branch, M. Branchesi, T. Briant, A. Brillet, M. Brinkmann, P. Brockill, E. Brockmueller, A. F. Brooks, D. D. Brown, M. L. Brozzetti, S. Brunett, G. Bruno, R. Bruntz, J. Bryant, Y. Bu, F. Bucci, A. Buchicchio, A. Buggiani, O. Bulashenko, T. Bulik, H. J. Bulten, A. Buonanno, K. Burtnyk, R. Buscicchio, N. Busdon, D. Buskulic, R. L. Byer, R. Cabrita, V. A. Cáceres-Barbosa, L. Cadonati, G. Cagnoli, C. Cahillane, A. Calafat, J. Calderón Bustillo, J. D. Callaghan, T. A. Callister, E. Calloni, S. R. Callos, K. Cannon, V. Cantory, H. Cao, L. A. Capistran, E. Capocasa, G. Capoccia, E. Capote, C. Capuano, G. Capurri, F. Carbognani, K. J. Cardona-Martínez, M. Carlassara, M. Carpinelli, G. Carrillo, G. Carullo, A. Casallas-Lagos, J. Casanueva Diaz, C. Casentini, S. Caudill, M. Cavaglià, R. Cavalieri, A. Ceja, G. Cella, P. Cerdá-Durán, E. Cesarini, N. Chabbra, W. Chaibi, A. Chakraborty, P. Chakraborty, S. Chakraborty, S. Chalathadka Subrahmanya, C. Chan, J. C. L. Chan, M. Chan, C.-Y. Chang, K. Chang, S. Chao, P. Charlton, E. Chassande-Mottin, C. Chatterjee, Debarati Chatterjee, Deep Chatterjee, M. Chaturvedi, S. Chaty, A. Chen, A. H.-Y. Chen, D. Chen, H. Chen, H. Y. Chen, S. Chen, Yanbei Chen, Yiwen Chen, G. Cheng, H. P. Cheng, P. Chessa, T. Cheunchitra, H. T. Cheung, S. Y. Cheung, F. Chiadini, G. Chiarini, A. Chiba, A. Chincarini, D. Chintala, A. Chiummo, A. Chopra, C. Chou, S. Choudhary, N. Christensen, Y. K. Chu, S. S. Y. Chua, G. Ciani, P. Ciecielag, M. Cieślar, M. Cifaldi, B. Cirok, F. Clara, J. A. Clark, T. A. Clarke, A. Claveus, M. R. Claypool, S. Clesse, F. Cleva, S. M. Clyne, E. Coccia, E. Codazzo, P.-F. Cohadon, D. E. Cohen, E. Colangeli, O. Cole, M. Colleoni, C. G. Collette, J. Collins, S. Colloms, A. Colombo, G. Compère, C. M. Compton, G. Connolly, L. Conti, T. R. Corbitt, I. Cordero-Carrión, S. Corezzi, N. J. Cornish, A. Corsi, S. Cortese, L. A. Corubolo, L. Cotnoir, R. Cottingham, J. A. Cotturone, M. W. Coughlin, P. Couvares, R. Coyne, A. Cozzumbo, J. D. E. Creighton, T. D. Creighton, S. Crook, R. Crouch, J. Csizmazia, K. Csukás, T. J. Cullen, A. Cumming, E. Cuoco, M. Cusinato, R. R. Cuzinatto, L. V. da Conceição, T. Dal Canton, S. Dall'Osso, S. Dal Pra, G. Dálya, Y. Dang, B. D'Angelo, S. Danilishin, O. Danner, S. D'Antonio, K. Danzmann, K. E. Darroch, L. P. Dartez, R. Das, S. Das, A. Dasgupta, V. Dattilo, A. Daumas, I. Dave, A. Davenport, T. F. Davies, D. Davis, M. C. Davis, P. Davis, E. J. Daw, M. Dax, J. De Bolle, E. deBruin, M. Deenadayalan, J. Degallaix, M. De Laurentis, C. J. Delgado Mendez, F. De Lillo, S. Della Torre, W. Del Pozzo, O. M. del Rio, A. Demagny, F. De Marco, G. Demasi, F. De Matteis, C. de Melo, N. Demos, T. Dent, A. Depasse, N. DePergola, R. De Pietri, R. De Rosa, C. De Rossi, E. K. Derrick, M. Desai, D. DeSantis, S. Deshmukh, V. Deshmukh, R. De Simone, S. Determan, S. Dhage, A. Dhani, R. Dhatri, R. Dhurkunde, R. Diab, C. Diaz, M. C. Díaz, F. Diaz Guerra, M. Di Cesare, M. A. Dicorato, T. Dietrich, C. Di Fronzo, M. Di Giovanni, D. Diksha, J. Ding, S. Di Pace, I. Di Palma, D. Di Piero, F. Di Renzo, Divyajyoti, A. Dmitriev, J. P. Docherty, Z. Doctor, N. Doerksen, E. Dohmen, A. Doke, A. Domiciano De Souza, L. D'Onofrio, F. Donovan, K. L. Dooley, S. Doravari, O. Dorosh, F. Dosopoulou, M. Drago, J. C. Driggers, M. Dubois, R. S. Dumbreck, U. Dupletsa, D. D'Urso, P. Dutta Roy, H. Duval, S. Dwivedi, S. E. Dwyer, C. Eassa, M. Eberhardt, M. Ebersold, M. Ebiri, G. Eddolls, A. Effler, J. Eichholz, H. Einsle, M. Eisenmann, M. Emma, K. Endo, R. Enficiaud, V. Ernst, L. Errico, R. Espinosa, M. Esposito, R. C. Essick, H. Estellés, T. Etzel, M. Evans, T. Evstafyeva, J. M. Ezquiaga, F. Fabrizi, V. Fafone, S. Fairhurst, X. Fan, A. M. Farah, B. Farr, W. M. Farr, M. Favata, M. Fays, M. Fazio, J. Feicht, M. M. Fejer, J.-N. Feldhusen, E. Fenyvesi, A. Feo, J. Fernandes, T. Fernandes, G. Fernández Rodríguez, D. Fernando, S. Ferraiuolo, T. A. Ferreira, M. Ferrer-Martinez, F. Fidecaro, P. Figura, I. Fiori, M. Fishbach, R. P. Fisher, S. K. Fitzgerald, V. Fiumara, R. Flaminio, E. Flanagan, S. M. Fleischer, L. S. Fleming, F. Flocco, E. Floden, H. Fong, J. A. Font, F. Fontinele-Nunes, C. Foo, B. Fornal, P. W. F. Forsyth, A. Fragkos, N. Franchini, A. Franco-Ordovas, F. Frappez, F. Frasconi, J. P. Freed, Z. Frei, A. Freise, O. Freitas, R. Frey, W. Frischhertz, P. Fritschel, V. V. 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Tacca, M. Tagliazucchi, H. Tagoshi, S. C. Tait, H. Takaba, K. Takada, H. Takahashi, R. Takahashi, A. Takamori, S. Takano, H. Takeda, I. Takimoto Schmiegelow, C. Talbot, M. Tamaki, N. Tamanini, D. Tanabe, K. Tanaka, S. J. Tanaka, S. Tanioka, D. B. Tanner, W. Tanner, L. Tao, R. D. Tapia, E. N. Tapia San Martín, A. Taruya, J. D. Tasson, J. G. Tau, A. Tejera, J. G. Temple, Y. Teng, H. Themann, A. Theodoropoulos, M. P. Thirugnanasambandam, L. M. Thomas, M. Thomas, P. Thomas, J. E. Thompson, S. R. Thondapu, E. Thrane, J. Tissino, A. Tiwari, Pawan Tiwari, Praveer Tiwari, S. Tiwari, V. Tiwari, M. R. Todd, E. Tofani, M. Toffano, A. M. Toivonen, K. Toland, T. Tomaru, V. Tommasini, H. Tong, C. I. Torrie, I. Tosta e Melo, E. Tournefier, A. Trapananti, R. Travaglini, F. Travasso, G. Traylor, L. Traylor, M. Trevor, M. C. Tringali, A. Tripathee, G. Troian, A. Trovato, L. Trozzo, R. J. Trudeau, T. Tsang, S. Tsuchida, K. Tsuji, L. Tsukada, A. Tuci, M. Turconi, C. Turski, H. Ubach, A. S. Ubhi, N. Uchikata, T. Uchiyama, R. P. Udall, T. Uehara, V. Undheim, V. Upadhyaya, L. E. Uronen, T. Ushiba, M. Vacatello, H. Vahlbruch, G. Vajente, J. Valencia, M. Valentini, E. Vallejo-Pagès, S. A. Vallejo-Peña, S. Vallero, M. van Dael, E. Van den Bossche, J. F. J. van den Brand, C. Van Den Broeck, M. van der Kolk, M. van der Sluys, A. Van de Walle, J. van Dongen, K. Vandra, M. VanDyke, H. van Haevermaet, J. V. van Heijningen, P. Van Hove, J. Vanier, J. Vanosky, N. van Remortel, M. Vardaro, A. F. Vargas, V. Varma, A. Vecchio, G. Vedovato, J. Veitch, P. J. Veitch, S. Venikoudis, P. Verdier, M. Vereecken, D. Verkindt, B. Verma, S. Verma, Y. Verma, S. M. Vermeulen, F. Vetrano, A. Veutro, A. Viceré, S. Vidyant, A. D. Viets, A. Vijaykumar, A. Vilkha, N. Villanueva Espinosa, E. T. Vincent, J.-Y. Vinet, S. Viret, S. Vitale, A. Vives, L. Vizmeg, B. Vizzone, H. Vocca, D. Voigt, E. R. G. von Reis, J. S. A. von Wrangel, W. E. Vossius, L. Vujeva, S. P. Vyatchanin, J. Wack, L. E. Wade, M. Wade, K. J. Wagner, L. Wallace, R.-Z. Wan, H. Wang, P. Wang, W. H. Wang, Y. F. Wang, Z. Wang, R. L. Ward, J. Warner, M. Was, T. Washimi, N. Y. Washington, D. Watarai, B. Weaver, S. A. Webster, N. L. Weickhardt, M. Weinert, A. J. Weinstein, R. Weiss, L. Wen, K. Wette, C. Wheeler, J. T. Whelan, B. F. Whiting, E. G. Wickens, D. Wilken, B. M. Williams, D. Williams, M. J. Williams, N. S. Williams, J. L. Willis, B. Willke, M. Wils, L. Wimmer, C. W. Winborn, A. Wingfield, J. Winterflood, C. C. Wipf, G. Woan, N. E. Wolfe, H. T. Wong, I. C. F. Wong, T. Wouters, J. L. Wright, M. Wright, B. Wu, C. Wu, D. S. Wu, H. Wu, K. Wu, Z. Wu, E. Wuchner, D. M. Wysocki, V. A. Xu, Y. Xu, N. Yadav, H. Yamamoto, K. Yamamoto, T. S. Yamamoto, T. Yamamoto, R. Yamazaki, T. Yan, H. Yang, K. Z. Yang, Y. Yang, Z. Yarbrough, J. Yébana Carrilero, A. B. Yelikar, X. Yin, J. Yokoyama, T. Yokozawa, M. Yoshihara, S. Yuan, H. Yuzurihara, M. Zanatta, M. Zanolin, M. Zeeshan, T. Zelenova, J.-P. Zendri, M. Zeoli, M. Zerrad, M. Zevin, H. Zhang, J. Zhang, L. Zhang, N. Zhang, R. Zhang, T. Zhang, C. Zhao, J. Zhao, Yue Zhao, Yuhang Zhao, L.-M. Zheng, Y. Zheng, L. Zhizhong, H. Zhong, H. Zhou, H. O. Zhu, X.-J. Zhu, Z.-H. Zhu, Z. Zhu, D. Z. Zieba, A. B. Zimmerman, L. Zimmermann, M. E. Zucker

Cosmology and Nongalactic Astrophysics

Inflationary Kicks and Coulomb Filtering of Spectator Dark Matter

Martina La Rosa, Rasheshwari Paul Chowdhury and Gianmassimo Tasinato

Light spectator fields provide a compelling inflationary origin for scalar dark matter, but their primordial fluctuations often generate excessive isocurvature perturbations on large scales. We develop a novel, exactly solvable filtering mechanism based on a tower of $\delta-$function contributions to the spectator mass, which we call kicks, whose dense limit converges to a smooth Coulomb-like profile. The filter produces a isocurvature spectrum during inflation that is strongly suppressed on large scales, rises with momenta as $k^3$ in the infrared, and, after a rapid turnover, smoothly approaches a constant plateau at small scales. This construction is motivated by a discrete translational invariance, admits an EFT regime in which radiative corrections can be systematically controlled, and can find a concrete realization in terms of an inflationary massive-clock model. We embed the filter in a minimal dark-matter scenario in which a spectator condensate oscillates about the minimum of a quadratic potential and behaves as pressureless matter. In this framework, the spectator dark-matter mass is directly related to the turnover scale of the inflationary isocurvature spectrum. We determine the resulting dark-matter abundance and analyze the relevant isocurvature and backreaction constraints. The most restrictive realization, in which the spectator condensate is generated during inflation, favors a relatively low inflationary scale.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Action-selected currents and a singular conservation closure in two-fluid energy–momentum-squared cosmology

Özgür Akarsu, Bilal Bulduk and Nihan Kat{\i}rc{\i}

In multi-fluid, matter-type gravity, the Bianchi identity constrains the divergence of the total effective stress tensor but does not, by itself, determine the currents assigned to its constituent sectors. Those currents are selected only after the off-shell matter action and equations, or an additional phenomenological closure, have been specified. We formulate this distinction and examine a spatially flat two-fluid background inspired by scale-independent EMSG. The case study combines an algebraic perfect-fluid prescription with a vanishing contracted-Hessian contribution, together with separate conservation of the total conventional and modification sectors. Because neither assumption is derived here from a concrete off-shell fluid action, the resulting system is an effective background closure rather than a microscopic EMSG model. For unequal EoS and every $\alpha\ne0$, the closure yields a Barrow-Clifton system whose transfer coefficients depend on $(w_1,w_2)$ but not on $\alpha$. Hence the nonzero-$\alpha$ family is singular: its $\alpha\to0$ limit does not recover the uncoupled GR conservation laws. We solve the two density eigenmodes and derive the associated modified Liénard equation for $H$. We also prove that the discriminant governing rank loss of the density-reconstruction map is strictly positive for every finite $w_1\ne w_2$. Thus each genuinely quadratic case has two distinct real rank-degenerate couplings. Exact vacuum and stiff-fluid families illustrate modal cancellation. When today's conventional densities are positive, the intervals on which both remain positive generally terminate at finite endpoints in the parameter ranges analyzed explicitly. These results provide a consistency diagnostic for separating action-level predictions from closure artifacts in multi-fluid, matter-type gravity; they do not establish an observationally viable EMSG model.
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Cosmology and Nongalactic Astrophysics

Black holes from a Higgs-like field in the radiation era

Ethan Milligan, Luis E. Padilla and David J. Mulryne

Light spectator fields during inflation can acquire superhorizon fluctuations that cross a potential barrier between positive and negative regions of their potential. Motivated by the Standard Model Higgs instability, in this work we study the subsequent evolution of patches where this occurs in the radiation era after inflation ends for a Higgs-like spectator field. We utilise fully nonlinear, spherically symmetric numerical relativity. Across the black hole forming configurations in our investigation we find a robust two-stage evolution. First, the central negative potential region reverses its expansion, becomes kinetic dominated, and forms a primordial black hole that hides the runaway core. The positive potential barrier that survives outside this first horizon then determines one of two late-time branches. In the subcritical branch the original apparent horizon grows smoothly and engulfs the remaining scalar structure. In the supercritical branch, however, the potential energy of the barrier dominates the local evolution. The result is a transient wormhole throat, a bifurcating trapping horizon, and an inflating child universe branch. In both branches the parent radiation dominated universe is ultimately left with an ordinary primordial black hole whose subsequent growth is governed by radiation accretion.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

Analytical Cosmological Collider at Strong Mixing in Laplace Space

Nathan Belrhali, Arthur Poisson and Sébastien Renaux-Petel

Primordial non-Gaussianities are at their largest when the curvature perturbation is coupled to a massive field by a mixing too strong to be treated perturbatively. We show that this regime, naturally reached in multifield inflation, is solved analytically by the Laplace-space representation we recently introduced, in which every mode becomes a superposition of plane waves weighted by a single kernel. The bispectrum then follows as a rapidly convergent series of elementary functions, in perfect agreement with independent numerical results. We find that the cosmological collider signal at strong mixing is larger than widely believed, with only half of the usual Boltzmann suppression. Its amplitude further grows with the number of time derivatives of the curvature perturbation in the interaction, singling out the most promising observational targets.
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Cosmology and Nongalactic Astrophysics

Dynamics of Wave Structures in Multifield Fuzzy Dark Matter Halos

Yu-Ming Yang, Xiao-Jun Bi and Peng-Fei Yin

As a natural extension of the single-field fuzzy dark matter (FDM) model, multifield FDM has attracted increasing attention in recent years. This scenario is motivated both by the axiverse scenario predicted by string theory and by the possibility that multifield FDM may provide a better match to astrophysical observations than its single-field counterpart. In this work, we perform high-resolution numerical simulations to systematically investigate the dynamics of wave structures in multifield FDM halos. In particular, we study the oscillatory and stochastic motions of the central core, the evolution and statistical properties of granules, and the resulting dynamical heating of embedded stellar systems. We find that the frequency spectra of the core density oscillations develop multiple peaks and shift toward higher frequencies relative to the single-field case. The centers of different field components undergo nearly synchronized random walks, while subdominant components exhibit larger random-walk amplitudes. We further show that the suppression of granule density fluctuations with increasing number of fields is largely insensitive to the fractional abundance of each component over a broad parameter range. Moreover, using self-consistent simulations, we find that the dynamical heating induced by granules is progressively suppressed as the number of fields increases. However, once the contribution from the central core is taken into account, this trend would become much less pronounced.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Impact of Bubble Nucleation History and Friction on Primordial Black Hole Formation

Tathagata Ghosh, Kousik Loho and Sudip Manna

Cosmological first-order phase transitions (FOPTs) in the early Universe are an exciting prediction of many beyond the Standard Model scenarios. Owing to the stochastic nature of bubble nucleation, some causal patches may remain trapped in the false vacuum long after the surrounding regions have completed the transition and started to redshift. Under suitable conditions, these delayed patches can become sufficiently overdense to collapse into primordial black holes (PBHs). One therefore expects characteristic parameters, such as the PBH mass and PBH formation time to be sensitive to the underlying phase-transition dynamics. Here, we adopt a model-independent framework with a fixed mean bubble separation scale ($R_*$) to directly compare the impact of exponential and Gaussian nucleation profiles on PBH formation. We further incorporate the effects of friction on the bubble walls arising from interactions with the surrounding plasma. We find that friction significantly modifies the bubble dynamics, leading to significant changes in the PBH mass and formation time for both nucleation histories. Moreover, the stochastic gravitational-wave spectrum generated by the FOPT can provide a complementary probe of the underlying dynamics, allowing the effects of friction on the bubble wall evolution to be distinguished from the frictionless case.
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Sunday 23 August

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Cosmological extra dimensions can mimic dark matter I. Dark matter in galaxies

Mattia Villani

We present a simple model with a n + 4-dimensional metric with compactified extra dimensions with a space dependent radius R. We show that changes in the profile of R are sourced by (visible) matter density and Newtonian potential. We can reproduce rotation curves of spiral galaxies and provide an expression for R. In order to test our hypothesis, we propose six experiments.
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Cosmology and Nongalactic Astrophysics

Constraining Gravitational Waves from Superconducting Cosmic Strings with the Dark Ages $21$-cm Signal

Adeela Afzal

Superconducting cosmic strings (SCSs) are characterized by three parameters: the dimensionless string tension $G\mu$, the current amplitude $Y$, and the vector coupling, $\tilde{e}$ as recently explored in \cite{Rybak:2024our}. Using the Charge-Velocity-dependent One-Scale (CVOS) model, we compute the stochastic gravitational wave background (SGWB) emitted by current-carrying loops, including the suppression effect of vector radiation. While previous studies have shown that large $\tilde{e}$ suppresses the SGWB, allowing larger $G\mu$ to evade pulsar timing array (PTA) bounds \cite{Rybak:2024our}, we demonstrate that this parameter space is definitively constrained by an independent, astrophysically clean probe: the Dark Ages global $21$-cm signal. We recalculated the recently derived $21$-cm bounds \cite{Si:2025vsj} into the generic $(\tilde{e},Y,G\mu)$ parameter space and find that at the threshold where vector radiation emission starts dominating, any coupling $\tilde{e}\gtrsim 10^{-7}$ and $Y\simeq 0.67$ and $G\mu\gtrsim 10^{-13}$ injects sufficient ionizing radiation to completely erase the $21$-cm absorption signal at redshift $z\simeq89$. Greater current amplitudes impose more stringent constraints. This excludes a large parameter space considered viable. Our model-independent results highlight the complementarity between future lunar-based $21$-cm experiments and gravitational wave (GW) observatories.
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Cosmology and Nongalactic Astrophysics

Primordial Asymmetries, Primordial Equation of State & Primordial Black Holes

Maël Gonin, Julien Froustey, Albert Escrivà et al. (+3 more)

We study the thermal history of the primordial Universe in the presence of non-zero lepton and baryon asymmetries. Considering different scenarios, we determine the equation of state (EoS) of the Universe from T = 10 GeV down to T = 1 keV, spanning the QCD transition, hadron gas phase and neutrino decoupling epochs. Using a combination of numerical codes, we track the cosmic trajectories of chemical potentials associated with the baryonic, leptonic and electric charges, and follow the evolution of lepton asymmetries including through the era where neutrino oscillations take place. Combining peak theory with numerical-relativity simulations of the collapse threshold, we show the EoS-induced modifications to the primordial black hole (PBH) mass spectrum. We determine the associated Gravitational Wave (GW) signal, showing how lepton asymmetries and a particular spectral index of curvature perturbations can be hinted at by current ground interferometer-based GW observations. Finally, we discuss constraints and positive evidence for PBHs.
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All authors Maël Gonin, Julien Froustey, Albert Escrivà, Alberto Magaraggia, Günther Hasinger, Florian Kühnel

Cosmology and Nongalactic Astrophysics

Anisotropies in the PTA gravitational wave background: what can they teach us about supermassive black hole binaries?

Matias Zaldarriaga and Gabriela Sato-Polito

The gravitational wave background detected by pulsar timing arrays is sourced by a finite population of supermassive black hole binaries, and is therefore anisotropic. We ask what measuring that anisotropy can teach us about the population, using models that span a wide range of effective source counts, all normalized to the measured background amplitude. We find four things. First, the expected anisotropy is produced by the single brightest binary: a dipole at the level of the published NANOGrav 95% upper limit would require one source to supply about 60% of the power in the band. Second, no model that also reproduces the measured strain spectrum contains a source that bright. In every case the loudest binary stays below the NANOGrav continuous-wave upper limit at every frequency it covers, consistent with the joint search of the 15-year data, which finds no resolved source. Third, because the anisotropy is produced by one source, compressing the sky to an angular power spectrum discards the phase information that locates it. Such a search is never more sensitive than looking for the source directly, and is strictly worse once more than a dipole is kept. Fourth, the published upper limits on the angular power spectrum therefore reflect the analysis prior rather than the data: they coincide with the 95th percentile of the prior induced by the square-root spherical harmonic basis adopted in the analysis. What does constrain the population today is the shape of the strain spectrum. Rare, bright sources depress the median spectrum below its mean, and fitting the measured spectrum already disfavors mass functions dominated by binaries above about 10^10 solar masses.
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Saturday 22 August

Cosmology and Nongalactic Astrophysics

Particle Dark Matter in the 1980s and 1990s

Michael S. Turner

In 1980, the Universe was made of stars, cosmology was the province of less than 100 astronomers, the Hubble constant was only known to within a factor of two, and the hot big bang was the “the standard model of cosmology.” Particle physics was a thriving enterprise concerned with the inner space of quarks, leptons and the strong, weak and electromagnetic interactions. The Standard Model was newly established and the aspirations were for a “grand unification” of the forces and particles. By 2000, the agendas of inner space and outer space were inextricably linked, and $\Lambda$CDM with its inflation, particle dark matter and dark energy – and a Hubble constant reliably known to better than 10% – was the new standard model. The big questions connecting inner space and outer space included the origin of ordinary matter, the identity of dark matter, the nature of dark energy, and an understanding of the origin of space, time and the Universe. Particle dark matter, the idea that the bulk of the mysterious dark matter is a new, long-lived or stable elementary particle, played a central in bringing together inner space and outer space, and today is still a hot topic in both fields.
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Cosmology and Nongalactic Astrophysics

Searching for signatures of self-interacting dark matter in halos from full-physics simulations: From 3D structure to projected observables

Giovanni Y. Ferron, Antonio Ragagnin, Lorenzo Pizzuti et al. (+1 more)

In this work we explore the imprints of self-interacting dark matter (SIDM) on the structure of simulated galaxy groups and clusters in view of future optical surveys. We find that both baryonic and projection effects lead to a significant alleviation of the SIDM core-forming behavior on the mass and density profiles, resulting in very small ($\lesssim 5\%$) deviations from standard collisionless dark matter. The opposite trend emerges for our most massive halos, where SIDM tends to significantly enhance the central density instead; we compare those halos with the observed dark matter profiles of two galaxy clusters, MACS J1206 and Abell S1063, finding that SIDM may leave potentially detectable imprints on cluster cores when considering the small observational uncertainty of current kinematic mass measurements. Finally, we find that weak lensing observations provide a promising tool for testing SIDM on cluster scales: in an idealized scenario where systematics are under control, weak lensing shear profiles exhibit up to $\sim 20\%$ level deviations for $M_{200} \gtrsim 10^{13}\ \text{M}_\odot$ halos. Conversely, the projected concentration-mass relation is only slightly modified by our SIDM models. We also discuss the limitiations of our analysis and the impact of the simulation resolution, as well as possible extension of this work. Overall, our results provide a baseline for future SIDM studies: although line-of-sight projection and baryonic effects significantly reduce SIDM imprints on halo mass profiles, weak lensing and kinematic analyses in galaxy clusters may potentially allow for robust detection and constraining of dark matter self-interactions in massive structures from megaparsec down to kiloparsec scales.
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All authors Giovanni Y. Ferron, Antonio Ragagnin, Lorenzo Pizzuti, Moritz S. Fischer

Cosmology and Nongalactic Astrophysics

Beyond dynamical dark energy: the role of dark sector interactions after DESI DR2

Weiqiang Yang, Sibo Zhang, Supriya Pan et al. (+2 more)

Recent DESI DR2 observations have renewed interest in extensions of the $\Lambda$CDM cosmological model, particularly through indications of a time-varying dark energy equation of state. In this work, we investigate whether such deviations may also involve interactions within the dark sector. We consider an interacting dark energy scenario in which the dark matter density evolves as $\rho_{\rm dm}\propto a^{-3+\delta}$, with the constant $\delta$ quantifying the interaction strength, and allow the dark energy equation of state to be either constant but different from $-1$, or dynamically evolving through the CPL parametrization. The models are constrained using Planck CMB data, DESI DR2 BAO measurements, and three Type Ia supernova compilations: PantheonPlus, Union3, and DES-Dovekie. For the constant equation-of-state case, the inclusion of DESI and supernova data leads to a preference for a small negative interaction parameter, with a significance above $2\sigma$. When dynamical dark energy is allowed, the evidence for interaction becomes weak, while the data favor a quintessence-like evolving dark energy component. In both scenarios, Bayesian model comparison still favors $\Lambda$CDM. Our results show that the inferred role of dark-sector interactions depends strongly on the nature of dark energy, highlighting the importance of jointly testing dark energy dynamics and interactions in the DESI era.
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All authors Weiqiang Yang, Sibo Zhang, Supriya Pan, Andronikos Paliathanasis, Emmanuel N. Saridakis

Cosmology and Nongalactic Astrophysics

Hydrodynamical simulations of the merging cluster El Gordo in a two-state self-interacting dark matter scenario

R. Valdarnini

A large suite of N-body/hydrodynamical simulations is used to demonstrate that the physical properties of the merging cluster El Gordo are well reproduced within a two-state self-interacting dark matter scenario. Our findings show that, in addition to elastic scattering, the presence of an inelastic, endothermic, up-scattering channel is essential to satisfy observational constraints derived from the measured weak lensing profiles of the two colliding clusters. We find that the observational properties of El Gordo are adequately matched by our self-interacting dark matter model within the following interval of parameters: an elastic cross-section in the range of ~ 4 -5 cm^2/gr, and an up-scattering channel bounded by an inelastic cross-section of approximately ~ 2 -4 cm^2/gr with a threshold velocity of ~1200 - 1600 kms, respectively. We argue that our conclusions depend critically on current uncertainties in the primary mass and the projected separation d_{DM}. In fact, our findings suggest that if error estimates in weak lensing measurements were significantly reduced - with future observations showing evidence of a low primary mass (<~ 10^{15} M_sun ) and a larger projected separation d_{DM} >~ 740 kpc - it would then be difficult for the proposed self-interacting scenario to be reconciled with observational constraints. We further suggest that future lensing surveys of massive, high-velocity merging clusters could be decisive in testing the proposed dark matter scenario.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

The Schwarzschild Black Hole in an External Gravitational Tidal Field: the Quasinormal Spectrum

Dimitrios Giataganas, Alex Kehagias and Antonio Riotto

A black hole need not ring down in isolation, since a nearby companion can subject it to an external gravitational tide. We calculate how a quadrupole tide modifies the Schwarzschild black hole resonances. Linearising the exact tidally distorted Schwarzschild solution in the tidal amplitude $A$, we derive the diagonal odd- and even-parity perturbation equations on the deformed background and compute the formal first order displacements of analytically continued Schwarzschild resonances. Each diagonal first order shift factorises as $\delta\omega_{n\ell m}=A\,c_{\ell m}\kappa_{n\ell}$, giving one reduced complex coefficient for each $(n,\ell)$, expressed as a ratio of contour integrals, multiplied by a universal Zeeman-like pattern that splits the $2\ell+1$ azimuthal multiplet. For the $\ell=2$ and $\ell=3$ sectors analysed explicitly, the odd- and even-parity shifts coincide, so Schwarzschild isospectrality survives at first order in the tidal amplitude. Quadratic tidal forces, by contrast, can break this degeneracy. Moreover, for a physical companion, the astrophysically dominant $(n,\ell,m)=(0,2,2)$ mode oscillates faster and decays more slowly. Finally, we show that the eikonal shifts admit a geometric description in terms of the Penrose limit about the tidally deformed photon ring.
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Friday 21 August

Cosmology and Nongalactic Astrophysics

Simulation Tests of PSF Modeling for Cosmic Shear with the Vera C. Rubin Observatory

Claire-Alice Hébert, Erin S. Sheldon, Tianqing Zhang et al. (+3 more)

Exceptional control of systematic effects is required in order to achieve unbiased cosmic shear two-point correlation function measurements with the next generation of galaxy imaging surveys, such as the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). One critical challenge is accurately modeling the point-spread function (PSF), as errors in PSF estimation can introduce spatially correlated biases in galaxy shape measurements. The LSST Science Pipelines, which will be used to process Rubin data, include an implementation of the PIFF (PSFs in the Full Field of View) package originally developed for, and demonstrated to perform well on, DES-Y3 and Y6 data. In this work we use semi-realistic image simulations, mimicking LSST observing conditions in $i$-band over 100 square degrees, to perform an end-to-end test of the Rubin PSF modeling pipeline. PSF model residuals are quantified using both second- and fourth-order moment parameters and performance is evaluated, for both LSST year 1 and year 10 depth, with a series of diagnostic tests. We find that the additive bias contribution from PSF modeling errors to the non-tomographic cosmic shear data vector is well below 30% of the cosmic shear uncertainty estimated from our analytic covariance matrix. Though our simulations exclude several known effects that may further challenge PSF modeling, these results demonstrate promising performance from PIFF on LSST-like data and provide an early benchmark for ongoing PSF validation efforts for LSST weak lensing analyses.
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All authors Claire-Alice Hébert, Erin S. Sheldon, Tianqing Zhang, Joachim Harnois-Déraps, Mike Jarvis, the LSST Dark Energy Science Collaboration

Cosmology and Nongalactic Astrophysics

High-Energy Neutrino Constraints on memory burdened Bardeen and Kerr Primordial Black Holes

Md Riajul Haque and Suvashis Maity

The quantum memory burden effect can suppress the late-time Hawking evaporation of primordial black holes (PBHs), allowing PBHs below the standard evaporation threshold of approximately $10^{15}\,\mathrm{g}$ to survive until the present epoch and potentially contribute to the dark matter abundance. We investigate primary and secondary neutrino emission from memory burdened Bardeen and Kerr PBHs, including Galactic and extragalactic fluxes and the effects of memory suppression, Bardeen regularization, and Kerr rotation. We constrain their abundance using observations from IceCube, Super-Kamiokande, and ANTARES, together with the projected sensitivities of IceCube-Gen2, GRAND200k, and Hyper-Kamiokande. We find that Bardeen regularization and Kerr rotation produce qualitatively different effects. Increasing the Bardeen parameter suppresses the Hawking temperature and neutrino flux, thereby weakening the abundance constraints. In contrast, rapidly rotating Kerr PBHs that retain a significant residual spin at the onset of the memory burdened phase can exhibit enhanced neutrino emission and substantially stronger constraints. Increasing the memory burden suppression index $k$ reduces the flux normalization but also allows lighter and hotter PBHs to survive, shifting the relevant signal toward higher energies. Consequently, HESE provides the leading sensitivity for weak suppression, whereas IceCube-Gen2 and GRAND200k become particularly important for stronger suppression. These results demonstrate the complementarity of current and future neutrino observations in probing memory burdened PBHs and the effects of regular geometry and rotation on their evaporation.
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