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Physics Astrophysics Cosmology and Nongalactic Astrophysics

astro-ph.CO Watch Cosmology and Nongalactic Astrophysics

Wednesday 26 August

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

REBELS-25: multi-phase morphology and kinematics at z = 7.31

Lucie E. Rowland, Hiddo S. B. Algera, Jacqueline Hodge et al. (+23 more)

We present a spatially resolved, multi-wavelength study of the massive, star-forming galaxy REBELS-25 at a redshift of $z=7.31$. We combine new high-resolution ALMA [O III]88$\mu$m observations with resolution-matched [C II], dust continuum, and JWST/NIRSpec IFU spectroscopy, providing a $\lesssim1$ kpc view of the morphology, interstellar medium (ISM) conditions, and multi-tracer gas kinematics of one of the most mature galaxies known in the reionisation era. We find differing morphologies from the rest-frame UV to far-infrared (FIR) emission, with the UV and optical emission appearing clumpy and irregular, whereas the FIR emission is well-described by near-exponential disc profiles, with [C II] being the most extended. Comparing the resolved UV and FIR emission, we find that obscured star formation contributes $\sim55$-$98$% of the total star formation rate across the galaxy, demonstrating that dust obscuration strongly shapes the observed UV and optical morphology. Resolved ionisation-line diagnostics show no significant variation across the source at $\sim1$ kpc resolution, consistent with broadly similar ISM conditions among the identified regions. Kinematic modelling reveals that both the warm ionised gas, traced by [O III]88$\mu$m, and the colder neutral gas, traced by [C II], share the same large-scale rotating structure and are dynamically cold, with ratios of ordered-to-random motion, $V/\sigma$, of $\sim11$ and 4.5, respectively, although we find evidence for non-circular motions that are not well-described by a simple rotating disc. Overall, these results further support a picture in which REBELS-25 hosts a dusty, chemically enriched, and dynamically cold ISM already in place at $z=7.31$.
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All authors Lucie E. Rowland, Hiddo S. B. Algera, Jacqueline Hodge, Mauro Stefanon, Rychard Bouwens, Manuel Aravena, Lucy Astles, Karin Cescon, Elisabete da Cunha, Ilse de Looze, Andrea Ferrara, Rebecca Fisher, Yoshinobu Fudamoto, Thomas Herard-Demanche, Hanae Inami, Mahsa Kohandel, Lena Komarova, Andrés Laza Ramos, Themiya Nanayakkara, Katherine Ormerod, Andrea Pallottini, Siân Phillips, Sander Schouws, Piyush Sharda, Renske Smit, Paul van der Werf

Cosmology and Nongalactic Astrophysics

An Inverse Lyth Bound for Non-Attractor Inflation

William H. Kinney

I present a novel physics result generated entirely autonomously by ChatGPT 5.6 Sol. The Lyth bound relates an observable primordial tensor amplitude to a lower limit on the field excursion during single-field slow-roll inflation. We show that non-attractor evolution obeys a complementary upper bound. For a canonically normalized scalar field, the nonconstant superhorizon curvature mode is anti-damped whenever the second Hubble-flow parameter satisfies $\epsilon_2\equiv d\ln\epsilon/dN<-3$. The same condition requires the inflaton kinetic energy to decrease sufficiently rapidly that the field-space distance traversed during a non-attractor interval obeys $\Delta\phi_{\rm NA} / M_{\text{P}} < \left(2\sqrt{2\epsilon_{\rm in}}/3\right) \left(1-e^{-3\Delta N/2}\right) < \left(2\sqrt{2\epsilon_{\rm in}}/3\right)$.The result is independent of the potential and does not require the slow-roll approximation. If $\epsilon_2=-p<-3$ is constant, the stronger bound $\Delta\phi/M_{\text{P}}<2\sqrt{2\epsilon_{\rm in}}/p$ is saturated asymptotically. In ultra-slow-roll inflation, $p=6$, giving $\Delta\phi<\sqrt{2\epsilon_{\rm in}}M_{\text{P}}/3$. We derive an exact relation between field excursion and amplification of the velocity of the nonconstant curvature mode, and give the corresponding scalar-power relation in the quasi-de Sitter limit. In contrast with the usual Lyth relation, arbitrarily large non-attractor amplification approaches a finite field distance. This provides a model-independent field-range constraint on canonical single-field mechanisms for amplifying primordial fluctuations.
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Cosmology and Nongalactic Astrophysics

Filaments within filaments: unraveling the hierarchy of the cosmic web

Saee Dhawalikar, Aseem Paranjape and Shadab Alam

Cosmic filaments are the most striking feature of the hierarchical cosmic web. Yet, their own sub-structure remains unexplored, unlike the well-known, universal halo/sub-halo hierarchy. We use a hierarchical reconstruction scheme to identify sub-filaments within larger filaments. Examining differences in the radial phase-space profiles of parent and sub-filaments, we argue that the latter constitute a statistically distinct class of structures. Establishing the existence of a universal filament hierarchy must then account for these differences, with implications for cosmology and dark matter.
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Cosmology and Nongalactic Astrophysics

Constraining primordial non-Gaussianity and energy injection with the thermal Sunyaev-Zeldovich effect and integrated Sachs-Wolfe effect cross-correlation

Ayodeji Ibitoye, Yin-Zhe Ma and Prabhakar Tiwari

Constraining primordial non-Gaussianity (PNG) provides key insights into the physics of cosmic inflation and the initial conditions of the Universe, which remain central topics in cosmology. In this study, we use the cross-correlation between the integrated Sachs-Wolfe (ISW) effect and the thermal Sunyaev-Zeldovich (tSZ) effect derived from Ibitoye et al. (2024) to jointly constrain PNG and early-Universe energy injection, including the standard intergalactic medium contribution. For scale-independent PNG we obtain $f_{\rm NL} = -358^{+140}_{-114}$ ($68\%$~C.L.). For a scale-dependent model ($f_{\rm NL}=f_{\rm NL}^{0}(\ell/\ell_{0})^{n_{\rm NL}}$, with $\ell_{0}=200$), we find $f^{0}_{\rm NL} = -296^{+173}_{-157}$ and $n_{\rm NL} = 0.62^{+1.02}_{-0.64}$, both consistent with Gaussian initial conditions. We also constrain the early-Universe energy injection amplitude to be $\alpha_{\rm inj} = -3.93^{+1.34}_{-0.99}$, with uncertainty reduced by a factor of $\sim\!2.6$ if Planck 2018 $f_{\rm NL}$ constraint is applied as a prior. Future surveys such as Simons Observatory and Euclid will tighten these constraints further. Complementary to conventional probes, this work provides the first ISW-tSZ constraint on exotic energy injection and enables precision tests of early-Universe physics while probing late-time gravitational potential and thermal energy perturbations.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE

The properties of the first continuous gravitational waves: Optimizing pulsar timing observations for supermassive black hole binary detection

Blaze Houlden, Eric Thrane and Katie Auchettl

Several pulsar timing arrays have reported evidence for a nanohertz gravitational-wave background. This background is thought to arise from the superposition of signals from a population of inspiraling supermassive black hole binaries. A key test of this interpretation is the search for individually resolvable binaries whose signals emerge above this background. Here we investigate this possibility by addressing two related questions: (1) what are the most probable properties of the first resolvable binary; and (2) how can pulsar timing observations be optimized to maximize its prospects for electromagnetic identification? By simulating populations of supermassive black hole binaries constrained by evidence for the gravitational-wave background and studying the loudest binary in each simulation, we infer the expected properties of the first individually resolvable systems. If MeerKAT continues its current observing strategy for a total of 9 years, the probability of detecting an individual binary is $\approx10-27\%$. Improving the timing precision by a factor of two changes this probability to $\approx11-28\%$, whereas increasing the cadence by a factor of four gives $\approx12-30\%$. Combining both improvements yields a detection probability of $\approx12-33\%$. Furthermore, implementing a high-cadence observing campaign preferentially resolves higher-frequency systems ($\gtrsim\unit[10]{nHz}$), whose shorter orbital periods make them considerably easier to identify through electromagnetic observations than lower-frequency binaries that repeat infrequently. We discuss prospects of electromagnetic follow-up of gravitational-wave resolved binaries with current high-cadence all-sky optical surveys.
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Cosmology and Nongalactic Astrophysics

Distinguishing cold and self-interacting dark matter through topological analysis

Adrian Szpilfidel, Clotilde Laigle, Pierre Boldrini et al. (+2 more)

Alternative dark matter (DM) models have emerged to solve the challenges faced by the predictions of collisionless cold dark matter (CDM) on galactic scales ($\lesssim 1$ Mpc). However, disentangling alternative models from CDM is difficult on such small scales because of the degeneracy with baryonic physics. It is therefore necessary to use DM probes that are not affected by baryons, e.g. that stand on intermediate scales, larger than galactic while remaining smaller than the scale at which the models converge to CDM. For the first time, we distinguish self-interacting DM (SIDM) from CDM using the genus statistic, a metric that characterises the topology of the density field. We carried out the analysis on the Darkium DM-only cosmological simulations, using one CDM model and four SIDM models with cross-sections of various amplitudes and velocity dependencies. We computed the genus on selected 3-virial radius wide regions centred around halos, for few hundred halos with masses ranging from $10^{12}$ to $10^{14}$ M$_\odot/h$ over redshifts $z=0$ to $z=2$. We also explored a more observation-like configuration, where the DM density field is traced only from the halo distribution in thick 2D projection since in principle redshift errors hinder a 3D reconstruction of the density field. We find that the density field is systematically clumpier in CDM than in SIDM models up to $0.05~\mathrm{Mpc}/h$, for halos of masses larger than $10^{12}$ M$_\odot/h$ at $z=0$. These predictions show that the genus of the density field is sensitive to DM self-interactions, suggesting that topological analysis could provide a valuable probe for distinguishing SIDM from CDM in observed halo distributions.
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All authors Adrian Szpilfidel, Clotilde Laigle, Pierre Boldrini, Moritz S. Fischer, Dmitri Pogosyan

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

Multi-messenger signal from QCD-Axion Ultracompact Minihalos

Dorian W. P. Amaral, Enrico D. Schiappacasse and Karla Tapia-Rebolledo

We explore the multimessenger signatures from ultracompact minihalos (UCMHs) seeded by stellar-mass primordial black holes (PBHs) and composed of QCD-axion dark matter. Using the secondary-infall framework, with relic-abundance and isocurvature conditions from a pre-inflationary Peccei-Quinn scenario, we numerically recover the characteristic halo profile and adopt a conservative constant-density core for the innermost region. We study the gravitational wave and electromagnetic signatures from neutron-star-PBH inspirals inside these dense structures. Dynamical friction produces a gravitational-wave dephasing relative to the vacuum binary, observable with LISA for primordial black holes with masses $\lesssim\! 10M_\odot$. Simultaneously, gravitationally focused axions can resonantly convert into photons in the neutron-star magnetosphere, producing a narrow-band radio signature. For nearby galactic neutron stars, the projected sensitivity of the Green Bank radio telescope GBT captures the QCD-axion band in the $\mu{\rm eV}$ mass range. Gravitational waves therefore probe the presence and structure of the UCMH, while the radio signal probes the particle nature of its dark matter, making their joint observation a distinctive test of a mixed dark sector.
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Cosmology and Nongalactic Astrophysics

The optimal redshift for dark energy II: application to cosmological data and the evidence for the phantom crossing of the CPL equation of state

Travis Seth Rippentrop, Mustapha Ishak and Kristian Gonzalez

Recent results from DESI and other cosmological datasets have indicated a preference for dynamical dark energy, with a time-evolving equation of state (EOS), $w(z)$. Furthermore, analyses using the CPL parameterization give an EOS with a phantom crossing of the $w(z)=-1$ line. In a companion paper-I, we assumed the CPL parameterization and its generalization, and introduced the formalism of the optimal scale factor (or redshift), a quantity designed to simultaneously maximize the distance from the cosmological constant value of $-1$ and to minimize the uncertainty on the EOS, thereby maximizing the tension with the cosmological constant at that specific redshift for a given dataset combination. In this paper-II, we apply the optimal-redshift formalism to available baryon acoustic oscillation, Cosmic Microwave Background, and supernova dataset combinations, with a particular focus on the phantom-line crossing within CPL. Motivated by the relatively low significance of previous constraints on the EOS in the region below the phantom line, we calculate the optimal redshift for a variety of dataset combinations to identify those that best constrain departures from $w(z)=-1$ before and after the crossing. We find combinations and corresponding optimal redshifts for which $w(z)$ lies below the “$-1$” line with new significance levels reaching $3.01$–$3.22\sigma$ before the crossing point, and $3.30$–$3.55\sigma$ above “$-1$" after the crossing. Our focus in this work is the application of a new framework that maximizes the significance of the phantom-crossing signal within CPL using currently available datasets. Determining whether this crossing is effective or intrinsic, and identifying the underlying microphysical models, constitute separate questions from the aim of the present work and remain important directions for future investigation, further motivated by our findings. Abridged.
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Tuesday 25 August

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

Engineering of titanium transition edge sensor wafers for the BA4-90/150 receiver of BICEP Array

A.Patel, P. A. R. Ade, Z. Ahmed et al. (+83 more)

BA4-90/150, the fourth receiver to be deployed in the BICEP Array (BA) series, is a dichroic 90/150 GHz instrument targeting the frequency space where sensitivity to the CMB polarization is maximized. The receiver will be deployed in the 2026-2027 austral summer, and is set to position BA to achieve exceptionally precise measurements of cosmic microwave background (CMB) polarization and strengthen constraints on inflationary models. Recent measurements in existing BA receivers suggest that unexpectedly high loop gain in the titanium (Ti) transition edge sensors (TESs) produces excess high-frequency noise that is consequently aliased down into the science band through the time-division multiplexed readout. To reduce the loop gain, we fabricated and tested prototype Ti TES wafers containing 16 modified detector architectures designed to broaden the superconducting transition and reduce the transition steepness (alpha). We present detector performance results, which will directly inform the final integrated wafer now being designed for full receiver commissioning.
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All authors A.Patel, P. A. R. Ade, Z. Ahmed, M. Amiri, D. Barkats, R. Basu Thakur, C. A. Bischoff, D. Beck, J. J. Bock, V. Buza, B. Cantrall, J. R. Cheshire IV, J. Connors, J. Cornelison, M. Crumrine, A. J. Cukierman, E. Denison, L. Duband, M. A. Echter, M. Eiben, B. D. Elwood, S. Fatigoni, J. P. Filippini, A. Fortes, M. Gao, C. Giannakopoulos, N. Goeckner-Wald, D. C. Goldfinger, S. Gratton, J. A. Grayson, A. Greathouse, P. K. Grimes, M. Halpern, S. Henderson, T. D. Hoang, J. Hubmayr, H. Hui, K. D. Irwin, M. Izquierdo Poza, J. H. Kang, K. S. Karkare, S. Kefeli, J. M. Kovac, C. Kuo, K. Lasko, K. Lau, M. Lautzenhiser, T. Liu, S. C. Mackey, N. Maher, K. G. Megerian, L. Minutolo, L. Moncelsi, Y. Nakato, H. T. Nguyen, R. O'Brient, S. N. Paine, M. A. Petroff, A. R. Polish, T. Prouve, C. Pryke, C. D. Reintsema, T. Romand, M. Salatino, A. Schillaci, B. Schmitt, B. Singari, A. Soliman, T. St. Germaine, A. Steiger, B. Steinbach, R. Sudiwala, K. L. Thompson, C. Tucker, A. D. Turner, C. Vergès, A. G. Vieregg, A. Wandui, A. C. Weber, J. Willmert, W. L. K. Wu, H. Yang, C. Yu, L. Zeng, C. Zhang, S. Zhang

Cosmology and Nongalactic Astrophysics

The optimal redshift for dark energy I: formalism and interpretation

Mustapha Ishak, Travis Seth Rippentrop and Kristian Gonzalez

We introduce the concept of the optimal redshift for dark energy, a statistically motivated redshift at which departures of the dark-energy equation of state (EOS) from the cosmological-constant value are tested most effectively. Within a generalized CPL parameterization, we derive an analytic expression for the optimal redshift by maximizing the separation of the EOS from $w=-1$ relative to the corresponding uncertainty. We establish the optimal redshift relationship to the phantom-crossing and pivot redshifts. As an illustration, we apply the formalism to the dataset combination of DESI DR2 BAO measurements, the DES Year-6 independent BAO measurement, and the recalibrated DES-Dovekie supernova sample. Adopting the null hypothesis $\mathcal{H}_0:w(a_{\rm opt})=-1$, we find a tension of ~$2.8\sigma$ with the cosmological-constant prediction at the optimal redshift, compared with ~$2.6\sigma$ at the pivot redshift, despite the latter having a smaller EOS uncertainty. This behavior reflects the specific design of the optimal redshift to maximize the statistical significance of a departure of the EOS from the -1 value of the $\Lambda$CDM model. We further provide statistical and geometrical interpretations of the optimum. In the CPL parameter space, the pivot corresponds to the projection that minimizes the variance of the equation of state, whereas the optimum maximizes its squared-distance from the cosmological-constant value over its variance. While the optimum is dataset and parameterization dependent, the underlying optimization principle and definition of the optimal redshift can be extended beyond the CPL framework. Future applications to DESI, Rubin LSST, Euclid, Roman Space Telescope, and other Stage-IV dark-energy surveys appear particularly promising.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

Tracing Galaxy Bias Through the Cosmic Web: The Role of Filaments

Constanza A. Soto-Suárez, Antonio D. Montero-Dorta, Daniela Galárraga-Espinosa et al. (+4 more)

The large-scale clustering of galaxies depends not only on their internal properties but also on their location within the cosmic web, which defines the anisotropic environments where galaxies form and evolve. Filaments serve as bridges through which galaxies and dark matter flow from low-density regions toward the highest-density nodes. In this work, we aim to map galaxy bias, which quantifies how these tracers follow the underlying dark matter density field, through the cosmic web, with a special emphasis on filaments. We look for dependencies on filament properties, such as length and density, and characterize the spatial variations of the large-scale bias along the filamentary spine. We applied the DisPerSE algorithm to identify the cosmic web in the TNG300 volume of the IllustrisTNG simulation. To measure large-scale galaxy bias, we utilized an object-by-object estimator, which provides advantages over standard estimators. We find that galaxies in node outskirts exhibit the highest large-scale bias values, reaching up to $\sim4$ times the values expected from theoretical models based on halo mass alone. Low-mass red galaxies in filaments and filament outskirts also display enhanced bias, which is strongly reduced after excluding galaxies close to nodes. Together, these results suggest that proximity to massive nodes plays a central role in shaping environmental secondary bias. Furthermore, galaxy bias decreases with filament length, from mean values of $1.4$ for short filaments to $-0.5$ for longer structures. This relation persists at fixed halo mass and galaxy color, and is not primarily driven by the average local galaxy density of the filament. Finally, short filaments exhibit an approximately uniform longitudinal bias profile, whereas long filaments show an increase in normalized bias from $\sim0.85$ near the saddle point to $\sim1.06$ close to the node.
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All authors Constanza A. Soto-Suárez, Antonio D. Montero-Dorta, Daniela Galárraga-Espinosa, Ignacio G. Alfaro, Andrés Balaguera-Antolínez, Ravi K. Sheth, Pablo López

Cosmology and Nongalactic Astrophysics

Cosmic topology. Part Va. Information content of the observable Universe

Deyan P. Mihaylov, Mikel Martin Barandiaran, Stefano Anselmi et al. (+14 more)

If the Universe possesses a compact spatial topology with characteristic scale not much larger than the diameter of the observable Universe, then the associated symmetry transformations imprint specific statistical correlations on density perturbations. We derive the covariance between perturbation modes in the full topology volume and compute the induced covariance between modes in the observable subvolume. We then use this covariance to estimate the available information about topology contained in the full set of observable linear perturbations. For two sample Euclidean examples - the cubic three-torus ($E_1$) and a three-torus with a quarter turn ($E_3$) - the three-dimensional density field carries enough information to detect topology on scales up to 25 percent larger than those accessible from the two-dimensional cosmic microwave background anisotropies alone. Future probes of the cosmic density field using deep galaxy surveys or neutral-hydrogen 21-cm intensity mapping, combined with computationally intensive searches over the large parameter space of admissible topologies, thus offer a plausible avenue to extending the range of detectable cosmic topologies.
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All authors Deyan P. Mihaylov, Mikel Martin Barandiaran, Stefano Anselmi, Javier Carron Duque, Glenn D. Starkman, Yashar Akrami, Craig J. Copi, Andrew H. Jaffe, Arthur Kosowsky, James B. Mertens, Anna Negro, George Alestas, Ricardo G. Rodrigues, Thiago S. Pereira, Amirhossein Samandar, Andrius Tamosiunas, Cynthia Trendafilova

Cosmology and Nongalactic Astrophysics

Quantifying the systematic impact of differential beam response on the BICEP CMB polarization data from 2016 through 2024

B. D. Elwood, P. A. R. Ade, Z. Ahmed et al. (+83 more)

As cosmic microwave background (CMB) polarization experiments, including BICEP3, BICEP Array, and future BICEP experiments, achieve ever-deeper polarization maps in search of primordial B-modes sourced from inflation, constraining instrumental systematics below statistical uncertainties becomes progressively more challenging. Since polarimetry in the BICEP telescopes is performed by pair-differencing co-located, orthogonally polarized detectors, differential beam response leads to temperature-to-polarization ($T \rightarrow P$) leakage, introducing a potential systematic bias on the inferred tensor-to-scalar ratio $r$. To mitigate this leakage, the lowest-order beam mismatch modes are filtered out of the CMB polarization maps through deprojection; however, residual undeprojected modes remain. To quantify this residual contamination, we perform dedicated in situ far-field beam measurements of the BICEP receivers during austral-summer calibration campaigns. We quantify the systematic impact of the undeprojected residuals with a specialized set of timestream simulations based on the measured per-detector beams. These "beam measurement-informed simulations" yield an estimate of the false polarized signal sourced by the undeprojected residuals. We summarize the beam measurements relevant to the BK24 data release and present preliminary residual-leakage results for BICEP3 at 95 GHz. For BICEP3 over 2016-2024, deprojecting all six standard templates together with readout-crosstalk templates and their radially smoothed counterparts reduces the equivalent-$r$ leakage amplitude from $\rho=(4.5\pm0.7)\times10^{-3}$ to $(1.12\pm0.06)\times10^{-3}$. We further describe an ongoing program to extend the deprojection basis beyond its historical six modes, guided by a forward optical model that relates candidate leakage modes to perturbations of physical instrument parameters.
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All authors B. D. Elwood, P. A. R. Ade, Z. Ahmed, M. Amiri, D. Barkats, R. Basu Thakur, C. A. Bischoff, D. Beck, J. J. Bock, V. Buza, B. Cantrall, J. R. Cheshire IV, J. Connors, J. Cornelison, M. Crumrine, A. J. Cukierman, E. Denison, L. Duband, M. A. Echter, M. Eiben, S. Fatigoni, J. P. Filippini, A. Fortes, M. Gao, C. Giannakopoulos, N. Goeckner-Wald, D. C. Goldfinger, S. Gratton, J. A. Grayson, A. Greathouse, P. K. Grimes, M. Halpern, S. Henderson, T. D. Hoang, J. Hubmayr, H. Hui, K. D. Irwin, M. Izquierdo Poza, J. H. Kang, K. S. Karkare, S. Kefeli, J. M. Kovac, C. Kuo, K. Lasko, K. Lau, M. Lautzenhiser, T. Liu, S. C. Mackey, N. Maher, K. G. Megerian, L. Minutolo, L. Moncelsi, Y. Nakato, H. T. Nguyen, R. O'Brient, S. N. Paine, A. Patel, M. A. Petroff, A. R. Polish, T. Prouve, C. Pryke, C. D. Reintsema, T. Romand, M. Salatino, A. Schillaci, B. Schmitt, B. Singari, A. Soliman, T. St. Germaine, A. Steiger, B. Steinbach, R. Sudiwala, K. L. Thompson, C. Tucker, A. D. Turner, C. Vergès, A. G. Vieregg, A. Wandui, A. C. Weber, J. Willmert, W. L. K. Wu, H. Yang, C. Yu, L. Zeng, C. Zhang, S. Zhang

Cosmology and Nongalactic Astrophysics · Cross-listed from physics.ins-det

Aliased noise characterization and mitigation in BICEP Array 150, 220 and 270 GHz time-division multiplexed detectors

S. Fatigoni, P. A. R. Ade, Z. Ahmed et al. (+83 more)

Early observations with the BICEP Array 150 GHz (BA2-150) and 220/270 GHz (BA3-220/270) receivers revealed detector noise equivalent temperatures (NETs) higher than expected, together with substantial detector-to-detector and module-to-module scatter. Noise measurements acquired with multiplexing off and high frequency sampling demonstrate that this excess originates from elevated high-frequency detector noise that aliases into the science band during time-division multiplexing. We show that the excess high-frequency noise is correlated with anomalously large logarithmic TES transition slopes, {\alpha}, resulting in elevated electrothermal loop gain and operation near the detector stability boundary. Measurements of {\alpha} indicate values substantially larger than expected, consistent with the sharper superconducting transitions introduced by the inverted TES fabrication process adopted for BA2-150 and BA3-220/270 detectors. Operational mitigation strategies were investigated through both increased multiplexing rates and elevated focal-plane operating temperatures. Faster multiplexing reduces aliasing by shifting the multiplexing Nyquist frequency beyond the excess noise roll-off, while elevated bath temperatures reduce TES electrical power and loop gain, improving detector stability and reducing NET by approximately 10%. These results demonstrate the importance of balancing TES responsivity, electrothermal stability, and multiplexed readout performance in next-generation CMB polarimeters.
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All authors S. Fatigoni, P. A. R. Ade, Z. Ahmed, M. Amiri, D. Barkats, R. Basu Thakur, C. A. Bischoff, D. Beck, J. J. Bock, V. Buza, B. Cantrall, J. R. Cheshire IV, J. Connors, J. Cornelison, M. Crumrine, A. J. Cukierman, E. Denison, L. Duband, M. A. Echter, M. Eiben, B. D. Elwood, J. P. Filippini, A. Fortes, M. Gao, C. Giannakopoulos, N. Goeckner-Wald, D. C. Goldfinger, S. Gratton, J. A. Grayson, A. Greathouse, P. K. Grimes, M. Halpern, S. Henderson, T. D. Hoang, J. Hubmayr, H. Hui, K. D. Irwin, M. Izquierdo Poza, J. H. Kang, K. S. Karkare, S. Kefeli, J. M. Kovac, C. Kuo, K. Lasko, K. Lau, M. Lautzenhiser, T. Liu, S. C. Mackey, N. Maher, K. G. Megerian, L. Minutolo, L. Moncelsi, Y. Nakato, H. T. Nguyen, R. O'Brient, S. N. Paine, A. Patel, M. A. Petroff, A. R. Polish, T. Prouve, C. Pryke, C. D. Reintsema, T. Romand, M. Salatino, A. Schillaci, B. Schmitt, B. Singari, A. Soliman, T. St. Germaine, A. Steiger, B. Steinbach, R. Sudiwala, K. L. Thompson, C. Tucker, A. D. Turner, C. Vergès, A. G. Vieregg, A. Wandui, A. C. Weber, J. Willmert, W. L. K. Wu, H. Yang, C. Yu, L. Zeng, C. Zhang, S. Zhang

Cosmology and Nongalactic Astrophysics

Slowly Rolling on a Quantum Correction

Ido Ben-Dayan, Ayushi Srivastava and Amresh Verma

Recent advances in cosmological measurements such as DESI and ACT may indicate an increase in the preferred value of the spectral tilt $n_s$ such that it disfavors rather popular models such as the Higgs or Starobinski inflation models. We argue that it actually means that the data is now sensitive enough to quantum corrections beyond simple tree-level models. Resurrecting the old theme of Coleman-Weinberg effective potential, we analyze the predictions of such models, as well as likelihood analysis, leading to a more established and interesting predictive framework.
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Cosmology and Nongalactic Astrophysics

Enhancing dark siren cosmology via Gaussian process reconstruction of incomplete galaxy catalogs

Matteo Tagliazucchi, Jonathan Gair, Riccardo Barbieri et al. (+1 more)

We present a novel framework for improving dark siren cosmology by applying a Gaussian process (GP) to the line-of-sight (LOS) reconstruction of incomplete galaxy catalogs. In the standard galaxy catalog method for inferring the Hubble constant $H_0$ from gravitational-wave (GW) dark sirens, missing galaxies are typically assumed to follow a uniform distribution in comoving volume, an assumption that discards galaxy redshift clustering information crucial for cosmological inference. We propose instead to model the LOS galaxy redshift distribution as a non-parametric function drawn from a GP realization, which is fitted to the observed incomplete catalog via a hierarchical Bayesian likelihood that explicitly accounts for the survey selection function. Applied to mock GW and galaxy catalogs extending up to redshift $z\leq0.4$, our method yields $H_0$ constraints that are on average 23% more precise than the standard homogeneous completion when using a 24%-complete galaxy catalog, and 37% more precise for an 8%-complete catalog. The largest improvement, reaching 66%, is obtained in configurations where the GP most effectively reconstructs the redshift over- and under-density features that the homogeneous completion fails to capture.
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All authors Matteo Tagliazucchi, Jonathan Gair, Riccardo Barbieri, Michele Moresco

Cosmology and Nongalactic Astrophysics

What would it take for dark matter to be literally warm?

Katelin Schutz

Warm dark matter (WDM) has served as a valuable benchmark for constraining small-scale structure in the past decades. In this note, I examine what it would take for dark matter to be warm in the literal sense assumed by that benchmark, i.e., a thermal relic that decoupled while relativistic. Satisfying current constraints on the WDM mass, which approach the $\sim$10 keV scale, requires one of three possibilities. One possibility is that there were $\sim 10^4$ relativistic degrees of freedom in the thermal bath at the time of decoupling, which is far beyond what is available in the Standard Model or plausible extensions of it. An alternative is that there was a period of early matter domination whose entropy injection diluted the relic density. However, in this scenario, the perturbations would have evolved through an expansion history that was different from the radiation-dominated one assumed in deriving WDM transfer functions. The third possibility is a dark sector that was never in thermal contact with the Standard Model and was simply born colder via asymmetric reheating. All of these possibilities rely on strong coincidences, where physics that has nothing to do with WDM happens to provide the exact initial conditions assumed in a WDM cosmology. Meanwhile, WDM is often used as a proxy for models with self-consistent thermal histories that generically predict the suppression of structure formation on small scales in a way that is both quantitatively and qualitatively different from WDM. I therefore advocate for a transition to more expressive parameterizations and simulation-based methods in order to extract more useful information from the wealth of upcoming data.
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Cosmology and Nongalactic Astrophysics

Impact of Scale-dependent Primordial Non-Gaussianity on Scalar-induced Gravitational Waves

Alisha Marriott-Best, Devanshu Sharma, Anish Ghoshal et al. (+1 more)

Scalar-induced gravitational waves (SIGWs) probe primordial curvature perturbations beyond cosmic microwave background scales, while primordial black holes (PBHs) probe the rare tail of the same statistics. We ask whether SIGW morphology can reveal scale-dependent primordial non-Gaussianity. We adopt the internal-leg separable kernel, $\mathcal F_{\rm NL}(\mathbf{k};\mathbf q,\mathbf{k}-\mathbf q)=\bar f_{\rm NL}f(q)f(\lVert\mathbf{k}-\mathbf q\rVert)$, and compute Gaussian, reducible, and connected contributions through $\mathcal O(\bar f_{\rm NL}^{4})$ in the second-order tensor-source approximation. We compare persistent power-law running with a UV-matched tanh weight that saturates at high scalar momentum. Across narrow, finite-width, asymmetric, and multi-slope scalar spectra, running produces more than amplitude renormalization. Power-law running shifts the scalar support sampled by non-Gaussian convolutions, generating peak displacement, asymmetric shoulders, and persistent ultraviolet deformations. The tanh template instead produces a transition-localized modification and approaches a momentum-independent ultraviolet plateau. Analytical estimates of the perturbative hierarchy, weighted slopes, log-normal saddle displacement, peak shifts, and infrared scaling explain the trends and the enhanced sensitivity of the $\mathcal O(\bar f_{\rm NL}^{4})$ sector. For localized sources with finite weighted moments, smooth running preserves the leading $k^3$ infrared behavior up to logarithmic corrections. Since the PBH mass scales as $M\propto k^{-2}$, preferential high-wavenumber weighting conditionally favors lower PBH masses in a narrow-support interpretation. Peak position, spectral curvature, shoulders, and ultraviolet slopes are diagnostics for PTAs, LISA, and third-generation observations, providing finite-order templates for primordial interactions on otherwise inaccessible scales.
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All authors Alisha Marriott-Best, Devanshu Sharma, Anish Ghoshal, Gianmassimo Tasinato

Cosmology and Nongalactic Astrophysics

The impact of the IGM thermal state on the Ly$\alpha$ flux 3D power spectrum from linear to highly non-linear scales

Tomáš Šoltinský, Gabriele Autieri, Vid Iršič et al. (+1 more)

Recently initiated and upcoming spectroscopic surveys, such as DESI and WST, will provide more than $10^6$ high-$z$ quasar spectra, enabling dense sky coverage by the Ly$\alpha$ forest. This is expected to establish the three-dimensional (3D) Ly$\alpha$ forest power spectrum, $P_{\rm 3D,\alpha}$, as a probe of the thermal and ionization history of the intergalactic medium (IGM). To exploit this opportunity, we quantify the imprints of reionization on the post-reionization IGM using high-fidelity numerical models. We use the Sherwood and Sherwood-Relics cosmological hydrodynamical simulations with box sizes up to $160\,h^{-1}\,\rm cMpc$ to investigate the impact of box size, mass resolution, and extracted grid resolution on $P_{\rm 3D,\alpha}$ over $2.4\leq z\leq4.8$. After applying a Zel'dovich control variate correction, simulation volume has a modest impact over most scales and orientations, whereas degrading the mass resolution produces differences of up to $\sim13\%$. Insufficient resolution of the grid used for the optical-depth calculation can artificially enhance small-scale power by up to $\sim35\%$. The timing of $\mathrm{H\,I}$ reionization leaves only a percent-level imprint on $P_{\rm 3D,\alpha}$ at $z=2.4$, whereas varying the photoheating rate by a factor of two changes the large-scale power by $\sim4-8\%$. Our results demonstrate that numerical effects can be comparable to, or exceed, the relic astrophysical signatures encoded in $P_{\rm 3D,\alpha}$, making numerical convergence essential for interpreting precise Ly$\alpha$ forest measurements. The strongest astrophysical imprint arises from spatially inhomogeneous $\mathrm{H\,I}$ reionization, which enhances the large-scale power by up to $\sim70\%$ at $z=4.2$. This highlights the potential of post-reionization Ly$\alpha$ forest measurements as a probe of the thermal history and spatial morphology of cosmic reionization.
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All authors Tomáš Šoltinský, Gabriele Autieri, Vid Iršič, Matteo Viel

Cosmology and Nongalactic Astrophysics

Chebyshev interpolation in Einstein-Boltzmann codes

Herman Sletmoen

Einstein-Boltzmann codes compute theoretical predictions of cosmological models and rely heavily on interpolation in their independent variables: time $\tau$, wavenumber $k$ and multipole $\ell$. We give a practical summary of interpolation with Chebyshev polynomials, which converges rapidly for smooth functions and thus pairs naturally with approximation-free Einstein-Boltzmann codes. By solving the perturbations and line-of-sight integrals at Chebyshev nodes in $k$ and $\ell$, we show that Chebyshev polynomials interpolate to higher precision than traditional cubic splines from fewer explicit solutions. On a set of example spectra for matter and the cosmic microwave background (CMB), we find up to four orders of magnitude lower interpolation error using the same number of points. For a typical CMB temperature spectrum computed with interpolation in both $k$ and $\ell$, Chebyshev polynomials converge to $10^{-4}$-$10^{-5}$ relative error with only 50-80 points per variable, while cubic splines approach $10^{-4}$ error with 200 points, translating to a $2.5\times$-$4\times$ speedup. The exact improvement depends on the target function and is generally more dramatic at high precision levels. Standard Chebyshev $\ell$-interpolation needs line-of-sight integrals generalized to non-integer $\ell$, but we show a way to avoid this by rounding the nodes to integers. Chebyshev interpolation is implemented in SymBoltz, which is available at https://github.com/hersle/SymBoltz.jl.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Testing $f(Q)$ Gravity with DESI DR2 and Strong-Lensing Time Delays

Darshan Kumar, Saibal Ray, Fengge Zhang et al. (+3 more)

Symmetric teleparallel gravity provides an alternative description of gravitation in which non-metricity replaces curvature and torsion. Its extension through $f(Q)$ gravity offers a different geometric description of the late-time expansion of the Universe and its accelerated phase. In this work, we investigate two $f(Q)$ models, a normalized power-law model and a square-root exponential model, and test their ability to describe the late-time expansion history. We constrain the model parameters through Markov chain Monte Carlo analyses using Cosmic Chronometer measurements, DESI DR2 baryon acoustic oscillations, strong-lensing time-delay observations, and three Type Ia supernova compilations, Pantheon$^+$, Union 3.0, and DES Y5. We compare both models with the flat $\Lambda$CDM model using the minimum $\chi^2$, Akaike information criterion, and Bayesian information criterion. The square-root exponential model provides a better statistical fit than $\Lambda$CDM for the combinations of Cosmic Chronometer, DESI DR2, and strong-lensing time-delay data with Pantheon$^+$ and Union 3.0, with improvements in both the goodness of fit and information criteria. The normalized power-law model remains statistically competitive with $\Lambda$CDM for the supernova-inclusive combinations, although the information criteria do not favor its additional parameter. We also determine the transition redshift from cosmic deceleration to acceleration for both models, obtaining consistent values across the different dataset combinations. The transition redshifts agree with observational estimates of the cosmic acceleration epoch. Overall, our results support $f(Q)$ gravity as a viable alternative to $\Lambda$CDM for explaining the late-time accelerated expansion of the Universe without requiring a cosmological constant.
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All authors Darshan Kumar, Saibal Ray, Fengge Zhang, Nisha Rani, Praveen Kumar Dhankar, Jie Zheng

Cosmology and Nongalactic Astrophysics

First application of weak lensing peak steepness statistics to HSC Y1 data: effectively probing halo density profiles

Ziwei Li, Xiangkun Liu, Tianyu Zhang et al. (+5 more)

As a new probe, the weak lensing (WL) peak steepness statistics is sensitive to the density profile of halos that encodes important information of baryonic feedback and dark matter properties, leading to a promising means to statistically constrain these effects using WL data. In this article, we present its first application to HSC Y1 data to demonstrate the great potential of this new statistics. Within the phenomenological framework of HMcode2016 that attributes the baryonic feedback solely to the reduction of the halo concentration parameter and focusing on high peaks originated dominantly from massive clusters, our analyses by combining WL peak height and steepness statistics resulted in $S_8=0.76^{+0.08}_{-0.07}$ with the maximum-a-posteriori (MAP) of $0.79$ and low concentrations. Taking the form of the concentration-mass relation as $c(M,z)=A(1+z_{\rm f})/(1+z)$ with $z_{\rm f}$ being the formation redshift of halos with mass $M$ at redshift $z$, we obtain $A=1.93^{+1.33}_{-1.16}$ (MAP=$1.70$) in comparison with $A=3.34^{+1.52}_{-1.74}$ (MAP=3.31) from dark matter only simulated mocks. The result tends to support phenomenologically strong baryonic feedback effects at cluster scales.
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All authors Ziwei Li, Xiangkun Liu, Tianyu Zhang, An Zhao, Chuzhong Pan, Shuo Yuan, Qiao Wang, Zuhui Fan

Cosmology and Nongalactic Astrophysics

CMB Birefringence from Axion String Networks Calibrated to an AMR Simulation

Mustafa A. Amin, Mudit Jain, Andrew J. Long et al. (+3 more)

A cosmological network of axion strings may exist in the Universe today. If axion-like particles couple to electromagnetism, such a network induces spatially varying birefringence in the polarization of the cosmic microwave background (CMB), which can be probed by current and next-generation CMB experiments. We calibrate a loop-crossing model against a large-scale adaptive-mesh-refinement (AMR) simulation of axion-string network dynamics in the early Universe and use the calibrated model to predict CMB birefringence from recombination to today. We find that the non-detection of anisotropic birefringence in CMB observations places a strong upper bound on the electromagnetic anomaly coefficient $\mathcal{A}$ that enters the axion-photon coupling $g_{a\gamma\gamma} = - \mathcal{A} \alpha_\mathrm{em} / \pi f_a$. A joint analysis of available anisotropic birefringence measurements constrains $|\mathcal{A}| < 0.24$ at 95% C.L., which is independent of the Peccei-Quinn scale $f_a$, assuming that the axions are hyperlight so that the network survives until today. This limit strongly restricts the high-energy embedding of hyperlight axions, excluding the minimal Grand Unified Theory prediction for the electromagnetic anomaly coefficient at high significance. In addition, we discuss the implications of an axion-string origin for the recently reported evidence of isotropic birefringence.
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All authors Mustafa A. Amin, Mudit Jain, Andrew J. Long, Aden Pugsley, Moira Venegas, Magdalena Whelley

Cosmology and Nongalactic Astrophysics

Gaussian process reconstruction of scalar field dynamics from recent cosmological data

Afaq Maqsood, Sonej Alam and Md. Wali Hossain

We reconstruct the late-time expansion history and dark energy dynamics using available cosmological data. We consider dark energy as an effective minimally coupled canonical scalar field without assuming a specific form for its potential. For reconstruction, we use Gaussian Process (GP) regression with a joint dataset consisting of 32 cosmic chronometer measurements (CC32), DESI DR2 baryon acoustic oscillation data, three Type Ia supernova compilations (Pantheon+, Union3, and DES Y5), and compressed CMB distance priors. From the reconstructed Hubble parameter and its derivatives, we obtain the scalar field kinetic and potential energy densities, the equation of state $w(z)$, and the dimensionless slope parameter $|\lambda(z)|$ of the scalar field potential. The reconstructed potential is nearly constant at late times, with $\tilde{V}(0) \simeq 0.68$–$0.70\rho_{c,0}$, close to the dark-energy density in flat $\Lambda$CDM. The kinetic term remains small over $0 \lesssim z \lesssim 2.5$, while $w(z)$ remains close to $-1$ within the uncertainties. Using only CC32 and DESI DR2, we find a mild ($1\sigma$) hint of a phantom-divide crossing near $z\sim0.5$. However, this feature depends on the supernova compilation and cannot be regarded as a firm conclusion with current data. The slope parameter $|\lambda(z)|$ shows mild evolution, with present-day central values around $0.8$–$1.0$, but large uncertainties due to its dependence on higher-order derivatives of the expansion history. The curvature parameter $\Gamma(z)$ requires even higher-order derivatives and is not constrained by current data; therefore, we do not report its reconstruction. Allowing small spatial curvature, $\Omega_k=0$–$0.02$, changes the results only slightly and remains within the existing uncertainty bands.
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Cosmology and Nongalactic Astrophysics

Dark-to-black super-accretion as a spin-imprinting mechanism for supermassive Kerr black holes

Saeed Fakhry, Nicolas Sanchis-Gual, Jorge Castelo Mourelle et al. (+2 more)

The existence of supermassive black holes with masses $M\gtrsim10^9\,M_{\odot}$ and large dimensionless spins $\chi\sim0.9-0.99$ at high redshift remains a challenge to our understanding of the early Universe. In this work, we study the adiabatic co-evolution of a Kerr black hole seed surrounded by two ultralight scalar dark matter clouds occupying different bound states, and show that this configuration allows the black hole to grow into the supermassive mass range while imprinting a characteristic final spin. The evolution proceeds through two stages. During the first stage, a spherical cloud described by the $\ell=0$ mode is completely depleted through a runaway dark-to-black accretion mechanism on a timescale of hundreds of millions of years for boson masses $\mu\sim10^{-18}-10^{-17}\,\mathrm{eV}$. Since the accreted material does not carry angular momentum, the black hole spin is universally driven to $\chi\simeq0$, independently of its initial spin. Throughout this stage, the second cloud, described by the $\ell=m=1$ mode, remains in the superradiant regime with negligible evolution. However, once the first stage is completed, this cloud transitions to the accreting regime, rapidly transferring both mass and angular momentum to the black hole. Starting from $\chi\simeq0$, the black hole spin increases until the evolution self-consistently saturates close to the threshold $\chi_{\rm sat}$, defined by the condition $\Omega_H(\chi_{\rm sat})=\mu$, on an e-folding timescale of thousands of years, orders of magnitude shorter than the first stage. This final saturation spin is largely independent of both the initial black hole spin and the mass of the secondary cloud, providing a spin-imprinting mechanism in which the primordial spin is first erased by spherical accretion and then reset to a value determined only by the boson mass and the final black hole mass.
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All authors Saeed Fakhry, Nicolas Sanchis-Gual, Jorge Castelo Mourelle, Darío Núñez, Juan Carlos Degollado

Cosmology and Nongalactic Astrophysics

The Primordial power spectrum from the largest to smallest CMB scales

Debabrata Chandra, Dhiraj Kumar Hazra, Arman Shafieloo et al. (+1 more)

We reconstruct the primordial power spectrum (PPS) across the full range of cosmological scales accessible to Cosmic Microwave Background (CMB) observations. Using the Modified Richardson–Lucy algorithm, we perform free-form reconstructions through deconvolution of Planck PR3 and PR4, Atacama Cosmology Telescope (ACT) DR6, and South Pole Telescope 3G (SPT-3G) D1 data. Across different regularization schemes, we find no evidence for significant deviations from a power-law primordial spectrum. The reconstructed spectra show a strong correlation between Planck and ACT, even at the level of localized features over their overlapping range, $0.07 < k < 0.14\,\mathrm{Mpc}^{-1}$, demonstrating consistency between the two observations. Using a complementary parametric Bayesian reconstruction, we find that the previously discussed preference for a blueward tilt in the ACT data at small scales is preferred only at the $1\sigma$ level.
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All authors Debabrata Chandra, Dhiraj Kumar Hazra, Arman Shafieloo, Tarun Souradeep

Cosmology and Nongalactic Astrophysics

A "MeerKAT-meets-LOFAR" Study of 2A 0335+096: Discovery of a Complex 500 kpc Radio Halo in a Disturbed Cool-Core Cluster

C. J. Riseley, R. J. van Weeren, L. Lovisari et al. (+9 more)

The emerging picture of radio haloes and mini-haloes in galaxy clusters is more blurred and far less distinct than once thought. While both trace cosmic ray electrons and magnetic fields in the intracluster medium (ICM), our knowledge of the mechanisms powering these sources, their properties and their connection to cluster dynamics, is incomplete. We present new deep MeerKAT L-band (856$-$1712\,MHz) observations of the sloshing cool-core cluster 2A~0335+096, performed as part of the “MeerKAT-meets-LOFAR” mini-halo census, as well as reprocessed LOFAR 120$-$168\,MHz LOFAR Two-metre Sky Survey data. We present highly sensitive radio continuum images, from which we perform a spectral analysis and a comparison of the thermal and non-thermal properties using reprocessed archival XMM-Newton data. Our MeerKAT data reveal that the known mini-halo is embedded in a large-scale radio halo spanning up to 510\,kpc in this sloshing cluster, although only the inner mini-halo is detected by LOFAR. We find a typical steep spectrum of $\alpha = -1.20 \pm 0.09$ for the mini-halo; the non-detection of the larger-scale halo by LOFAR indicates a spectral index no steeper than $-1.2$. Our results are broadly consistent with an interpretation of turbulent (re-)acceleration powered by sloshing within the cluster potential well. This work emphasises the need for using deep, high-dynamic multi-frequency radio observations in conjunction with high-quality X-ray observations to complete our understanding of the connection between radio halo properties and cluster dynamics.
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All authors C. J. Riseley, R. J. van Weeren, L. Lovisari, R. Timmerman, A. Botteon, A. Bonafede, A. Ignesti, N. Biava, G. Brunetti, B. Colquhoun, Y. Perrott, T. Vernstrom

Cosmology and Nongalactic Astrophysics

The Effect of Slitless Spectroscopic Redshift Uncertainty and Interlopers on BAO Measurements from CSST-like Samples

Zhejie Ding, Yu Yu and Pengjie Zhang

The baryon acoustic oscillations (BAO) is a vital probe to measure cosmological distances and constrain dark energy. The ongoing and near-future space-based telescopes, including the Chinese Space Station Survey Telescope (CSST), will perform galaxy redshift surveys using slitless spectroscopy. Due to the relatively low spectral resolution and observational effects, there will be uncertainties and interloper contamination in measured redshifts. In this study, we consider the Gaussian-distributed redshift uncertainty and [O III]-H$\beta$ interlopers in the CSST-like slitless spectroscopic redshift (spec-z) samples, which are simulated using the approximate $N$-body code FastPM. We study the effect of spec-z errors on BAO before and after density field reconstruction. Both the redshift uncertainty and interlopers can damp the BAO signal, and the latter can further induce oscillations in the broadband shape of the power spectrum. We model the interloper effect on the propagator, i.e. the cross-correlation between the observed and initial density fields, as well as on the BAO power spectrum. We study the influence of the spec-z errors on the fitted anisotropic BAO parameters $\alpha_{\perp}$ and $\alpha_{\parallel}$. The resulting systematic bias on $\alpha_{\perp}$ and $\alpha_{\parallel}$ is mild, mostly within $0.1$ per cent and $0.2$ per cent, respectively. Even with the spec-z errors, BAO reconstruction can still significantly reduce the systematic bias and statistical errors on the $\alpha$ parameters. Furthermore, we vary the redshift uncertainty and study the reconstruction performance.
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Cosmology and Nongalactic Astrophysics

Projected Constraints on Primordial Black Holes from Scalar-Induced Gravitational Waves with Taiji

Yang Jiang, Chen Yuan and Qing-Guo Huang

Scalar-induced gravitational waves (SIGWs) provide a direct probe of the enhanced primordial curvature perturbations that may also produce primordial black holes (PBHs). We forecast the capability of the space-based gravitational-wave observatory Taiji to search for an SIGW background generated by a broken-power-law curvature spectrum. A signal-injection study is used to validate the analysis pipeline, after which a pure-noise realization is employed to derive projected upper limits on the curvature-spectrum parameters. We translate these limits into constraints on the PBH abundance using the nonlinear compaction function, critical collapse, and the joint Gaussian distribution of the compaction amplitude and curvature at its peak. The resulting projected $95\%$ upper limits on the PBH dark-matter fraction satisfy $f_{\mathrm{PBH}}^{95\%}<1$ over PBH masses from approximately $6.2\times10^{-18}\,M_\odot$ to $1.7\times10^{-8}\,M_\odot$. We compare the forecast with representative Hawking-evaporation and microlensing bounds. In part of the asteroid-mass interval, the projected Taiji limit is more restrictive than the current Subaru Hyper Suprime-Cam (HSC) microlensing constraint.
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Monday 24 August

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

Is MOND an Emergent Effective Law of a Complex Dark Matter Sector?

V.K. Oikonomou and Eleni I. Manouri

In this work we aim to present a new perspective for MOND theory, namely that MOND theory is not an answer for the missing matter at galactic scales, but it provides a phenomenological description of the dynamics that DM should produce at galactic scales. We also aim to point out that MOND dynamics at galactic scales is achieved by scale-dependent self-interacting dark matter, which can behave as collisionless and collisional, depending on the scales and the physical processes. To this end, we first aim to highlight the successes of the $\Lambda$-Cold-Dark-Matter model and how it overwhelms over the MOND paradigm. Using textbook physics, we present the successes of the $\Lambda$-Cold-Dark-Matter at cosmological and cluster scales, and how these phenomena cannot be described consistently by MOND theories. Thus, by excluding MOND as being a viable description of nature at all scales, we conclude that MOND may not be the answer behind missing matter in Newtonian galactic dynamics, but it is just showing how the dynamics of dark matter should behave at galactic scales.
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