Cosmology and Nongalactic Astrophysics
Inflationary Axion Isocurvature in the CMB across All Ultralight Masses
Rayne Liu, Wayne Hu and Daniel Grin
If the Peccei-Quinn
symmetry of an ultralight
axion is broken before the end of inflation,
axion quantum fluctuations seed isocurvature perturbations, linking them to the tensor-to-scalar ratio $r$. We extend the effective time average (ETA) approach of the Boltzmann code ${\rm AxiECAMB}$ to accurately evolve these perturbations across the full
axion mass range from dark energy ($m_a \lesssim H_0$) to dark matter ($m_a \gg 10^{-28}$ eV) types. We provide analytic fitting formulae for the
axion abundance given the initial field value $\phi_{\rm ini}$, accurate at sub-percent level for $m_a \gg H_0$ and allowed dark matter fraction $f_{\rm dm}$. In the dark matter regime, the Planck bound on CDM isocurvature requires $r\ f_{\rm dm} < 0.08\,(m_a/10^{-27}\,{\rm eV})^{-1/2}$, which becomes stronger than the current BICEP tensor bound for $m_a f_{\rm dm}^2 \gtrsim 10^{-26.4}\,{\rm eV}$. For $10^{-32} \lesssim m_a/{\rm eV} \lesssim 10^{-28}$, Jeans suppression breaks the degeneracy with CDM isocurvature, leaving unique signatures, and in the dark energy regime ($m_a \lesssim H_0$), the isocurvature signal is even more highly suppressed, peaking only at the CMB quadrupole. We provide analytic scalings for both signatures. Given the tensor bound, any primary CMB detection in these two lightest regimes would indicate a non-inflationary origin of the isocurvature modes or a breakdown of the standard frozen-field misalignment scenario. A window of coexistence opens near $m_a \sim 10^{-25}$ eV and $f_{\rm dm} \gtrsim 0.1$ where both
axion isocurvature and tensor modes could be discovered just below current bounds while simultaneously alleviating the $S_8$ tension.
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Cosmology and Nongalactic Astrophysics
The Impact of Splashback Galaxies on Galaxy Assembly Bias
Hernan Rincon, Idit Zehavi, Sergio Contreras et al. (+2 more)
The clustering of
galaxies is affected by the assembly history of their underlying dark matter
halos. This complex phenomenon, known as
galaxy assembly bias, has been extensively studied, but the exact physical origin remains unclear. Splashback
halos, typically low-mass
halos that have traversed larger neighboring
halos, have been suggested to be associated with
halo assembly bias. Using a semi-analytic
galaxy-formation model applied to the Millennium simulation, we explicitly explore the role that splasback
galaxies play in
galaxy assembly bias. We identify splashbacks as present-day central
galaxies that were formerly satellites of a more massive host, and construct stellar-mass selected
galaxy samples with the splashbacks either removed or reclassified as satellites of their former host
halo. We find that splashbacks tend to reside in low-mass, highly concentrated
halos and in dense environments, and that they have relatively high stellar-to-
halo mass ratios. Splashbacks appear to be largely responsible for the low-mass tail of the occupancy variation for highly concentrated
halos and for
halos in dense environments. Finally, when computing the impact of assembly bias on
galaxy clustering, we find that while removing the splashbacks significantly reduces the signal, reassigning them has little effect on its amplitude but shifts the transition scale. We repeat the analysis with the hydrodynamical simulation TNG300, confirming the robustness of our results. Our results provide insight into assembly bias and have potential implications for modeling the
galaxy-
halo connection.
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All authors Hernan Rincon, Idit Zehavi, Sergio Contreras, Yikun Wang, Xiaoju Xu
Cosmology and Nongalactic Astrophysics
Axion dark matter search with a photonic bandgap cavity haloscope and dielectric tuning rod over 10.25-10.45 GHz
Morgan Lynn, Ankur Agrawal, Arjun Ghosh et al. (+4 more)
We report the development of a new widely tunable cavity and demonstrate its use in a search for dark matter
axions. We achieve unloaded quality factors above $10^{5}$, roughly $25\times$ larger than a bare copper cavity at the same frequency, using concentric sapphire shells to reduce Ohmic losses on the cavity barrel. A rotating sapphire rod tunes our cavity mode over the $10.1-11.7$ GHz range, approximately $16\%$ of its resonant frequency. Using an amplified receiver chain, we demonstrate sensitivity to new
axion parameter space by tuning the cavity over the $200$ MHz range between $10.25-10.45$ GHz (42.4 - 43.2, $\mu$eV) to constrain the
axion-to-
photon coupling to $|g_{a\gamma\gamma}|$ $\leq$ 1 $\times$ $10^{-12}$ ${GeV}^{-1}$. This cavity can scan its tuning range about $9$ times faster compared to a bare copper cavity when paired with a
photon counting device, laying the groundwork for a definitive search for the QCD
axion over $10.1-11.7$ GHz.
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All authors Morgan Lynn, Ankur Agrawal, Arjun Ghosh, Sara Sussman, Steven G. Johnson, David I. Schuster, Aaron S. Chou
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
The large-scale ordered magnetic field in the Galactic halo and the Local Bubble
Elena Orlando
All-sky synchrotron polarization observations are the primary probe of the Galactic large-scale ordered
magnetic field, which includes both coherent and ordered random components. However,
magnetic-field strength estimates from synchrotron observations depend on the assumed
cosmic-ray electron model, which itself depends on the
magnetic-field configuration and strength throughout the
Galaxy. We aim to constrain the strength of the large-scale ordered
magnetic field in the Galactic
halo through a self-consistent treatment of
cosmic-ray electrons with the latest coherent
magnetic-field configuration inferred by Xu & Han from rotation measures corrected for local contamination. We compare the Planck 30 GHz synchrotron polarization maps with our large-scale synchrotron models that jointly treat
cosmic rays and
magnetic fields and are constrained by direct
cosmic-ray measurements and multifrequency data. Since the inferred field strength depends on the
halo size, we explore different
cosmic-ray propagation
halo sizes. We observe a significant large-scale synchrotron excess relative to model predictions, which requires an ordered toroidal
magnetic-field component in the
halo with a peak strength of 3.2-4.3 microG, depending on the assumed
halo size. We also find that the
cosmic-ray propagation model with a 4 kpc
halo size is preferred by the Planck synchrotron polarization maps. This result shows that the ordered
magnetic field is 4-6 times stronger than the coherent field inferred from rotation measures by Xu & Han, establishing the presence of an ordered random field in the Galactic
halo that is not traced by rotation measures. Attributing the synchrotron excess entirely to the Local Bubble would require non-standard Local Bubble properties, disfavoring this interpretation.
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Cosmology and Nongalactic Astrophysics
Probability of gravitational-wave lensing by intermediate-mass black holes and globular clusters
Luka Vujeva, Jose María Ezquiaga, Rico K. L. Lo et al. (+1 more)
Strongly lensed gravitational waves (GWs) are powerful probes of substructure in the lens. Intermediate-mass black holes (IMBHs) are postulated to be efficient lenses that may distort the lensed waveforms of currently detectable stellar-mass compact binaries, as hinted by GW231123. Assuming that IMBHs are located in globular clusters (GCs), we compute the rate at which they would affect strongly lensed repeated chirps produced by
galaxy-scale lenses, considering a compound lens system. Exploring different astrophysical model assumptions and
lensing criteria, we find that the relative rate is at most 1/1000 and decays to 1/10,000 for our fiducial optimistic scenario. At high magnifications, $\mu$ > 100, the relative rate approaches 1%, but these cases are intrinsically rare in absolute value. Our results imply that GW
lensing by IMBHs and GCs is unlikely, disfavoring such an interpretation for GW231123. In turn, they point towards lensed GWs being a clean probe of dark matter substructures and primordial black holes.
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All authors Luka Vujeva, Jose María Ezquiaga, Rico K. L. Lo, Lorenz Zwick
Cosmology and Nongalactic Astrophysics
Deus ex $H_0$ – Is evidence for dynamical dark energy conditioned on early cosmology?
Nils Schöneberg, Rodrigo Calderón and Julien Lesgourgues
Some free-form reconstructions of the dark energy equation of state suggest that dynamical dark energy is the only explanation for the observed data. In this letter we argue that early Universe solutions to the Hubble tension (around or before recombination) generically cause the evidence for this claim to strongly reduce, establishing a tight connection between the early and late cosmology. In particular, the level of evidence for dynamical dark energy depends on the parameters $H_0 r_\mathrm{d}$ and $\Omega_\mathrm{m}$ and early universe solutions typically push towards higher values of $H_0 r_\mathrm{d}$ and lower values of $\Omega_\mathrm{m}$, where such evidence is reduced.
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Cosmology and Nongalactic Astrophysics
HST imaging, pipeline modeling, and time-delay predictions of 2 triply-imaged and 15 quadruply-imaged lensed quasars
William Sheu, Tommaso Treu, Adriano Agnello et al. (+10 more)
The Hubble tension remains a significant challenge in modern cosmology, exhibiting a discrepancy between early-Universe
cosmic microwave background measurements and local distance ladder observations. Strong
lensing time-delay cosmography provides an independent,
geometric probe of $H_0$ that can help resolve this discrepancy. Although hundreds of lensed
quasars have been discovered, only a handful have been analyzed due to the resource-intensive follow-up required to measure precise time delays and break degeneracies. We present uniform gravitational lens modeling of 17 recently discovered lensed
quasar systems (2 triply-imaged and 15 quadruply-imaged) to identify and prioritize the most promising candidates for future cosmological study. Using high-resolution near-infrared Hubble Space
Telescope WFC3/IR F160W imaging (PID: 17916, PI: T. Treu), we perform uniform pipeline modeling with Lenstronomy. We constrain the mass and light profiles of the deflector
galaxies, and assuming a fiducial cosmology, we predict their Fermat potential differences and expected time delays. Our pipeline successfully yields models and time-delay predictions for all 17 systems. Assuming ideal monitoring conditions, we estimate the total contribution from time-delay and Fermat potential modeling errors to the time-delay distance. From this, we classify the systems by estimated time-delay distance uncertainties: six "excellent" ($\leq 3\%$), five "good" ($3\%$-$7\%$), three "suitable" ($7\%$-$12\%$), and three "impractical" ($>12\%$). We recommend prioritizing follow-up campaigns on the 11 "excellent" and "good" systems, which have the potential to deliver high-precision, independent constraints on $H_0$ to help resolve the Hubble tension.
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All authors William Sheu, Tommaso Treu, Adriano Agnello, Timo Anguita, Simon Birrer, Daniel Gilman, Xiaosheng Huang, Richard G. McMahon, Nicholas D. Morgan, Veronica Motta, Anna Nierenberg, Kenneth C. Wong, Ioana Zelko
Cosmology and Nongalactic Astrophysics
Sensitivity of Next-Generation CMB Surveys to Neutrinos and Other Light Relics
Cynthia Trendafilova, Srinivasan Raghunathan, Benjamin Wallisch et al. (+33 more)
Neutrinos and other light relics leave characteristic imprints in the
cosmic microwave background anisotropies, making their observation a sensitive probe of the particle content and thermal history of the early universe. The energy density in these relativistic species is parameterized by their effective number $N_\mathrm{eff}$. Measuring this parameter at the percent level, which is a long-standing science goal of CMB-S4 and other experiments, would test a wide range of well-motivated physics within and beyond the Standard Model of particle physics. In this paper, we present Fisher-
matrix forecasts of the projected sensitivity to $N_\mathrm{eff}$ of several CMB-S4 survey configurations considered during its extensive design phase. The conceptual design reaches $\sigma(N_\mathrm{eff}) < 0.03$ over its seven-year observing period, while the revised configuration achieves the same precision over a longer timescale. We complement these results with a
cosmic-variance-limited survey over the same multipole range to quantify the room for improvement accessible with additional instrumental, observational, and theoretical efforts. Finally, we discuss the broad implications of precise $N_\mathrm{eff}$ measurements for the radiation sector, big bang nucleosynthesis, light thermal relics, and other early-universe physics. The forecasts presented in this work are performed with the publicly released DRAFT (Dark Radiation Anisotropy Flowdown Team) tool. It provides an end-to-end pipeline from simulated foreground maps and component separation to delensing and projected sensitivities for any cosmological parameter, and it can be directly applied to other
cosmic microwave background survey designs.
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All authors Cynthia Trendafilova, Srinivasan Raghunathan, Benjamin Wallisch, Joel Meyers, Kevork N. Abazajian, Edoardo Altamura, Carlo Baccigalupi, Kimberly K. Boddy, Thejs Brinckmann, Yuji Chinone, Gabriele Coppi, Francis-Yan Cyr-Racine, Jacques Delabrouille, Katherine Freese, Helena García Escudero, Martina Gerbino, Shamik Ghosh, Vera Gluscevic, Daniel Green, Daniel Grin, Kevin M. Huffenberger, Mudit Jain, Lloyd Knox, Anto I. Lonappan, Marilena Loverde, Philip Lubin, Gabriele Montefalcone, Valentine Novosad, Marco Raveri, Christian L. Reichardt, Sayan Saha, Murali M. Saravanan, Emmanuel Schaan, Sara M. Simon, Julien Tang, Scott Watson
Cosmology and Nongalactic Astrophysics
Simplified treatment of kinematic corrections to the SZ effect using the boost operator approach
Alex Hoey, Jacob Long and Jens Chluba
The Sunyaev-Zeldovich (SZ) effects provide a potent cosmological probe of the large-scale structure in the universe. Here, we present a simplified derivation of the kinematic corrections to the relativistic thermal SZ effect using the boost operator approach. By first performing the thermal average inside the moving electron cloud frame, the thermal and peculiar motion contributions can be naturally separated, leading to a significant simplification of the scattering calculation. The angular dependence of the problem is resummed into the pre-computed Doppler operators avoiding the otherwise cumbersome many-dimensional angular integrals required using conventional approaches. We provide expressions for the relativistic SZ signal, exact to all orders in the electron temperature theta_e and the peculiar velocity beta_p of a given cluster. These reproduce well-known results for the relativistic SZ effects and extend the description to higher orders in the cluster's speed. We also derive a closed-form expression for the thermally-averaged thermal SZ scattering operator by studying the underlying
symmetries of the Doppler operators fundamental to the formalism. Through these results, we also demonstrate how the boost operator approach gives clarity to the physical description of the problem at hand, promising to be useful to a wide range of astrophysical problems.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Inflation with Nieh-Yan-like terms in metric-affine gravity
Ilaria Andrei, Christian Dioguardi, Damianos Iosifidis et al. (+3 more)
We study single-field slow-roll inflation in metric-affine
gravity with a scalar field non-minimally coupled to the non-Riemannian Ricci scalar and to the divergences of the torsion and nonmetricity vectors, a structure that generalizes the well-known Nieh-Yan term. By imposing projective coherence of the matter sector and solving the connection field equations, we integrate out torsion and nonmetricity and obtain an equivalent Einstein-frame formulation in which the metric-affine couplings are encoded in a modified kinetic function and potential. For the choice of coupling functions $\mathcal{A}(\phi) = M_P^2 + \xi \phi^2$ to the non-Riemannian Ricci scalar, $\mathcal{C}_i(\phi) = \xi_i \phi$ to the Nieh-Yan-like terms and a monomial Jordan-frame potential $\mathcal{V} \propto \phi^k$, we show that in the limit of a large positive effective Nieh-Yan-like coupling $\bar{\xi}$ the canonical field satisfies $\chi \sim \phi^2$, the Jordan-frame field values during inflation become sub-Planckian, and the Einstein-frame potential reduces to $U \sim \chi^{k/2}$. We compute the slow-roll predictions numerically for quartic and quadratic Jordan-frame potentials and compare them with the current CMB constraints from Planck, BICEP/Keck, ACT, and SPT. We find that intermediate values of $\bar{\xi}$ can restore the compatibility of non-minimally coupled Palatini inflation with observations: in the quartic case, the model predicts a tensor-to-scalar ratio within reach of next-generation CMB experiments for $\bar{\xi}\lesssim10^4$, while in the quadratic case the coupling cures the $\eta$-problem arising for $\xi \gtrsim 10^{-2}$ and yields viable predictions for $10^{-2}\lesssim\bar{\xi}\lesssim 10^2$. In the negative $\bar{\xi}$ regime, the model does not improve upon standard Palatini inflation, though it can still produce distinct, testable predictions.
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All authors Ilaria Andrei, Christian Dioguardi, Damianos Iosifidis, Laur Järv, Antonio Racioppi, Margus Saal
Cosmology and Nongalactic Astrophysics
KiDS-1000: Improved constraints on cosmology, intrinsic alignments and baryonic feedback from clipped cosmic shear
Benjamin Giblin, Joachim Harnois-Déraps, Louise Paquereau et al. (+1 more)
We present improved cosmological constraints from the fourth data release of the Kilo-Degree Survey ("KiDS-1000") using "clipped" shear correlation functions. Clipping filters the projected density field inferred from weak
lensing data for the highest-density regions, allowing for two-point functions to extract additional cosmological information. We model, for the first time, the impact of systematics on clipped
lensing statistics, including intrinsic
alignments, baryonic feedback, photometric
redshift uncertainties, and source-lens clustering. We train Gaussian process emulators on dark-matter-only and hydrodynamical $N$-body simulations to predict the cosmological and systematic dependence of both the clipped and conventional, "unclipped" shear correlation functions. We find that the combination of the clipped and unclipped probes improves the constraints on the free parameters of the $w$CDM model relative to the conventional approach, with a 16% tightening of the $S_8$ uncertainty and 24% for $w_0$. Our constraints, $\Omega_{\rm m} = 0.263^{+0.035}_{-0.038}$, $S_8=0.724^{+0.027}_{-0.027}$, and $w_0 = -1.24^{+0.26}_{-0.28}$, are consistent with the $\Lambda$CDM model and with the
cosmic shear analysis of Asgari et al. (2021) via a completely independent simulation- and emulator-based forward-modelling approach. We also find the complimentary information in the clipped statistic provides an upper limit on the baryon feedback strength, and improves the constraints on intrinsic
alignments by 27%.
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All authors Benjamin Giblin, Joachim Harnois-Déraps, Louise Paquereau, Catherine Heymans
Cosmology and Nongalactic Astrophysics
Sample Variance Cancellation for Future Spectroscopic Surveys
James M. Sullivan and Martin White
High-
redshift spectroscopic
galaxy surveys will be the scientific engines of the next generation of large-scale structure cosmology. The clustering signal of high
redshift,
star-forming Lyman-$\alpha$ emitters (LAEs) will be of key importance for obtaining high-
redshift constraints on the growth of structure and
redshift-space distortions. The complex radiative transfer (RT) of Lyman-$\alpha$
photons alters the
symmetry group respected by the overdensity field constructed from these
galaxies, and so the observed large-scale clustering of LAEs may have an angular dependence that differs significantly from that of linear theory, possibly biasing inference of cosmological parameters. While such an effect has been seen in simulations, its amplitude in nature and its detailed form remains unclear. In the restricted context of a linear, Gaussian model, we outline a procedure for pinning down the type and amplitude of such changes in angular dependence on large scales due to unknown RT or a more general unmodeled angular effect in the hypothetical scenario in which an observer is presented with LAE data containing such an effect. We show that if a second tracer without the modified angular dependence is available for cross correlation with the LAEs at the same
redshifts (e.g., Lyman-break
galaxies), then, with a high
redshift survey of modest size, it is possible to rapidly identify: 1) the presence of a nontrivial angular functional form of radiative transfer (by a conditional field-level realization), 2) the functional form itself (with an optimal filter that we derive), and 3) the value of its amplitude with an uncertainty (via an adaptation of the standard quadratic
estimator). Such sample-variance-cancellation strategies therefore provide a statistical solution to unknown astrophysical or systematic angular clustering dependence, including from RT.
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Cosmology and Nongalactic Astrophysics
Conformal Killing Gravity: New Constraints from DESI DR2 BAO datasets
Himanshu Chaudhary, Salvatore Capozziello, Carlo Alberto Mantica et al. (+3 more)
We investigate a
geometric approach referred to as the Conformal Killing
Gravity (CKG), in which the dark energy sector emerges naturally from the conformal Killing
symmetry of the Robertson–Walker space-time. Within this framework, the divergence-free conformal Killing tensor behaves as an effective perfect fluid, giving rise to a dynamical dark-energy component whose density, pressure, and equation of state are uniquely determined by the underlying geometry, without introducing any empirical dark-energy parametrization. The resulting CKG model extends the standard $\Lambda$CDM cosmology through a single additional parameter while recovering the $\Lambda$CDM limit in the absence of the
geometric contribution. We constrain the model using Planck PR4 (NPIPE) CMB temperature, polarization, and
lensing observations, ACT DR6 CMB
lensing, DESI DR2 baryon acoustic oscillation measurements, and the Pantheon$+$, DES-Dovekie, and Union3 Type Ia
supernova compilations. The analysis shows that the CKG favors a quintessence-like dark-energy
evolution with no evidence for phantom crossing, while the reconstructed equation of state rapidly approaches the cosmological constant at earlier
cosmic times. Furthermore, the model predicts a future critical
redshift in the range $-0.8 \lesssim z_c \lesssim -0.7$, indicating that the present
cosmic expansion eventually reaches a turning point before the formal singular limit at $z=-1$. Since the
geometric contribution modifies only the post-recombination expansion history, the sound horizon remains essentially unchanged and the model does not provide a complete solution to the $H_0$ tension. Our results demonstrate that the CKG provides a simple, physically motivated, and observationally favored framework for describing the late-time accelerated expansion of the Universe.
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All authors Himanshu Chaudhary, Salvatore Capozziello, Carlo Alberto Mantica, Luca Guido Molinari, Dhruba Jyoti Gogoi, Ghulam Mustafa
Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
Testing dark matter models and modified gravity theories with spatially resolved HI observations
Federico Lelli, Antonino Marasco, Timothy A. Davis et al. (+8 more)
Understanding the nature of dark matter (DM) is one of the most pressing questions of modern physics. The flat rotation curves of
galaxies, especially the extended HI rotation curves from
radio observations at 21 cm, played a key historical role to establish the DM problem and continue to be a major tool to test different
galaxy formation models, particle DM models, and modified
gravity theories. The SKA observatory will revolutionize the study of HI rotation curves thanks to its unprecedented angular resolution, sensitivity, and survey speed. In combination with optical and near-infrared ancillary data, HI surveys with SKA-Mid AA4 will allow us to (1) obtain HI data at spatial resolutions of 1"-2", probing the inner
galaxy dynamics with unprecedented details (e.g., the cusp-core problem); (2) move from representative samples of a few hundreds of objects to statistical samples of tens of thousands of objects, allowing us to study the dynamical scaling laws of
galaxies and their DM properties with unprecedented statistical power across different
cosmic environments; (3) move from
galaxies at z~0 to
galaxies at z~1, probing DM
halos at earlier
cosmic epochs and exploring the
redshift evolution of the dynamical laws across about 8 Gyrs. The massive SKA data, however, will pose important technical challenges for the derivation of HI rotation curves with automated kinematic software. Developing such kinematic software in the SKA era will be crucial to reach major scientific goals, such as discriminating between different solutions to the DM problem.
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All authors Federico Lelli, Antonino Marasco, Timothy A. Davis, Nathan Deg, Jonathan Freundlich, Gyula I. G. Jòzsa, Peter Kamphuis, Pavel E. Mancera Piña, Stacy S. McGaugh, Amidou Sorgho, Kristine Spekkens
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Magnetic Catalysis and Fermion Mass Generation in de Sitter Spacetime
Kohei Fujikura, Toshifumi Noumi and Shintetsu Yamazaki
We consider the dynamics of a charged
fermion in de Sitter space in the presence of a uniform background
magnetic field, and discuss
magnetic catalysis of chiral
symmetry breaking using the Nambu–Jona-Lasinio (NJL) model. We evaluate the mode functions of the charged
fermion field in this background by imposing the Bunch–Davies
vacuum condition. The gap equation is solved in the mean-field approximation. We derive analytic expressions for the gap in several limiting regimes, such as the large-
magnetic-field and large-
curvature limits. We find that the
curvature effect restores chiral
symmetry, whereas the
magnetic field enhances chiral
symmetry breaking through the conventional mechanism of
magnetic catalysis. The phase structure associated with chiral
symmetry breaking is revealed by numerical calculations.
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Cosmology and Nongalactic Astrophysics
Tensor-Induced Backreaction in Ultra-Slow-Roll Inflation
Alessandro Ciaiolo and Giovanni Marozzi
We discuss the impact of tensor-induced backreaction at second order in perturbation theory on primordial black holes production in single-field inflationary models, where the comoving
curvature power spectrum is amplified by a transient ultra-slow-roll phase. Although the leading perturbative correction is mostly negligible in standard slow-roll
evolution, it becomes important in non-attractor regimes, going in the direction of limiting the suppression of the first slow-roll parameter $\varepsilon$ and reducing the enhancement of the scalar power spectrum. We then go beyond the standard perturbative analysis by considering the background parameters as effective quantities with
evolution self consistently determined by a closed system of backreaction equations. This analysis, which leads to a partial resummation of the effect beyond the perturbative treatment, confirms the limitation of the suppression of $\varepsilon$ by consistently showing how the effect remains important even after accounting for the effective
evolution of the background in the evaluation of the backreaction itself. Finally, we discuss how, taking into account the tensor-induced backreaction, the fine-tuning associated with the value of the peak amplitude of the scalar power spectrum is strongly reduced.
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Cosmology and Nongalactic Astrophysics
Redshift Dependence of $H_0$ Dipole in Pantheon+ Supernovae
M.H. Jalali-Kanafi, E. Ó Colgáin, S. Pourojaghi et al. (+1 more)
We examine the dipole structure in the local
cosmic expansion rate $H_0$ using the Pantheon+ compilation of Type Ia
supernovae. We reconstruct directional maps of $H_0$ across the sky within the low-
redshift regime, $z_{\rm min} < z < 0.2$, evaluated in the CMB rest frame. To perform a tomographic analysis, we choose 10 different values for $z_{\rm min}\in [0.015 , 0.045]$ range. We find a dipole amplitude $A_{\rm dip}=1.16\pm0.28\ {\rm km/s/Mpc}$ for the lowest bin, monotonically decreasing to $A_{\rm dip} =0.35\pm0.52\ {\rm km/s/Mpc}$, as we increase $z_{\rm min}$. Since $A_{\rm dip}$ is positive-definite, by construction $A_{\rm dip} > 0$ even in an isotropic universe, thus to assess the statistical significance, we compare to $A_{\rm dip}$ generated from 1000 Monte Carlo simulations based on the $\Lambda$CDM model and the same
redshift ranges. Our results reveal a $2-3\sigma$ dipole pattern (depending on how the significance level is computed) for $z_{\rm min}\lesssim 0.032$. For
redshift thresholds where the signal remains statistically significant ($>2\sigma$), the inferred dipole direction points close to Shapley supercluster and CMB dipole directions. As $z_{\rm min}$ increases, the dipole amplitude diminishes in line with expectations of a higher
redshift isotropic Universe, but the difference in maximal antipodal $H_0$ determinations, $\Delta\text{H}_0^{\rm max}$, retain a signal of an anisotropy that disappears in the dipole ansatz. The decreasing statistical significance of all
estimators with increasing $z_{\rm min}$ suggests that any $H_0$ dipole is a low-
redshift feature.
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All authors M.H. Jalali-Kanafi, E. Ó Colgáin, S. Pourojaghi, M.M. Sheikh-Jabbari
Cosmology and Nongalactic Astrophysics
Revisiting 2D and 3D Dainotti Correlations for GRBs Using Bayesian Neural Networks
Nilanjana Bagchi Aurpa, Abha Dev Habib and Nisha Rani
Gamma-ray bursts (GRBs) are promising cosmological probes, but their use as standard candles is limited by the circularity problem, necessitating model-independent calibration of GRB luminosity correlations. We revisit the two-dimensional (2D) and three-dimensional (3D) Dainotti correlations using
Bayesian Neural Networks (BNNs) trained on the updated Observational Hubble Data (OHD) and Pantheon+ Type Ia
Supernova sample. The reconstructed luminosity distances are used to calibrate the Platinum and Narendra et al. GRB samples. We constrain the parameters of the 2D Dainotti relation and the 3D fundamental plane, and examine the impact of calibration
datasets and GRB sample selection. Calibration achieved using Pantheon+ yields tighter constraints than OHD, while the 3D correlation exhibits lower intrinsic scatter than the 2D relation. Our results demonstrate that BNNs provide a robust framework for model independent calibration of GRB luminosity correlations with reliable uncertainty propagation. Further, the underlying distance probe is a key factor in model-independent calibration, determining both the size of the GRB samples and the precision of the resulting constraints.
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Cosmology and Nongalactic Astrophysics
Cosmography for a General Spacetime Centred at Arbitrary Redshift
Jonas Broe Bendtsen, Asta Heinesen and Sofie Marie Koksbang
With upcoming surveys providing large volumes of highly precise observational data across a wide range of
redshifts, it is increasingly important to have tools that can translate observational data into
geometric and dynamical information without imposing a predetermined cosmological model. General cosmographic expansions centred at arbitrary
redshift provide exactly such a tool. We here present the formalism for general cosmographic expansions centred at an arbitrary
redshift, valid for 4-dimensional Lorentzian spacetimes. We then apply the expansion formalism to test its ability to reproduce the
redshift-distance relation in two examples of large-scale
cosmic structures (an underdensity and an overdensity) modelled by the Lemaître-Tolman-Bondi metric, where we examine the effect of choosing different
redshift intervals for the cosmographic series expansions. This quantifies the extent to which cosmographic coefficients inferred from
redshift-distance observations retain their interpretation as local
geometric and dynamical quantities, as is expected in standard FLRW cosmology. Similarly to earlier results, we here find that in more general spacetimes the coefficients instead become effective parameters reflecting the finite observational range probed. Lastly, we discuss possible strategies for using the expansions to constrain dynamical and
geometric quantities.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA
Smoothed particle magnetohydrodynamics for simulations of galaxy and cosmic structure formation
Orestis A. Karapiperis, Matthieu Schaller, Nikyta Shchutskyi et al. (+2 more)
We introduce a novel formulation of cosmological smoothed particle magnetohydrodynamics (SPMHD), designed to model
magnetic field physics in a vast array of nonlinear astrophysical systems, and which we have implemented in the highly-parallel, entirely modular, and open-source simulation code SWIFT. Our numerical scheme is designed to offer optimal performance at a minimal computational cost, keep a low
memory footprint, and most notably couple robustly to effective sub-resolution recipes of
galaxy formation. This is achieved through expressing our
evolution equations in a density-energy conservative form, and augmenting them with discontinuity-capturing terms tailored to high dynamic range simulations, which are further modulated by adaptive switches that drastically improve coupling to sub-grid models and limit spurious dissipation. We moreover present novel suggestions for the two major regularisation techniques used in modern SPMHD, namely a tensile instability correction and mixed
hyperbolic/parabolic divergence-cleaning scheme, to ensure code stability in highly dynamical scenarios. We evaluate the performance of our method on a series of problems of increasing complexity, culminating in three astrophysical applications which have historically proven challenging for mesh-less methods: we study jet launching from a forming proto-stellar core, dynamo amplification in a massive
galaxy cluster and
magnetic field
evolution in a Milky Way-like disk
galaxy; the latter constitutes the first reported coupling of the EAGLE
galaxy formation model to a magnetohydrodynamics solver. Keeping model hyperparameters fixed across our test suite to provide a transparent picture of our method's capabilities in production, we demonstrate sound performance and convergence with resolution on standard `laboratory' numerical experiments, as well as competitive capabilities in realistic applications.
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All authors Orestis A. Karapiperis, Matthieu Schaller, Nikyta Shchutskyi, Federico A. Stasyszyn, Maarten Elion
Cosmology and Nongalactic Astrophysics
Joint Geometric and Dynamical Constraints on Cosmology from Anisotropies in Galaxy Intrinsic-Alignment Correlations
Teppei Okumura
We present the first joint cosmological analysis to extract both
geometric and dynamical information from
galaxy intrinsic
alignments (IAs). Using BOSS spectroscopy cross-matched with
galaxy shape measurements from the DESI Legacy Imaging Surveys, we measure anisotropic
galaxy density–intrinsic ellipticity (GI) and intrinsic ellipticity (II) correlations over $0.43\leq z\leq0.7$ and decompose their
spin-dependent angular structure into associated Legendre multipoles. The measured GI correlation exhibits the expected baryon acoustic oscillation (BAO) structure, while its anisotropy provides
geometric information complementary to
galaxy clustering. By jointly modeling
redshift-space and Alcock-Paczynski distortions, we constrain the growth rate parameter $f\sigma_8$, the angular-diameter distance $D_A$, and the Hubble expansion rate $H$. Relative to
galaxy clustering alone, adding IA reduces their fractional uncertainties by 32%, 18%, and 29%, respectively. By mapping these constraints onto a flat $w_0$CDM model, IA also tightens the constraints on $w_0$, $\Omega_m$, and $H_0$; however, the $w_0$ constraint is sensitive to the minimum scale included in the analysis. Our results establish anisotropic
galaxy shapes as an additional source of
geometric and dynamical information for spectroscopic cosmology.
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Cosmology and Nongalactic Astrophysics
Optical Signatures of Sgr A* and M87* with Dark Matter Halos
Noraiz Tahir, Muhammad Ali Paracha and Mubasher Jamil
The event horizon
telescope (EHT) has opened a new window onto the strong-field regime by imaging the shadows of the supermassive black holes (SMBHs) Sgr A* and M87*. These observations provide a unique laboratory for probing the dark matter (DM) distribution around black holes. In this work we systematically investigate the imprints of two distinct DM
halo models, the cold DM (CDM), and the cored scalar field DM (SFDM) profiles on the gravitational
lensing signatures of Sgr A* and M87*. We compute the
photon spheres, shadows, weak and strong
lensing observables, and caustic structures for both models. We then compared the obtained values of the shadow diameters with the EHT data, using $\chi^2$ statistics. We found that all the models are within $1.2\sigma$ of the measured shadow diameters with the small $\chi^2$ differences, $\Delta\chi^2 \lesssim 1.2$. The caustic analysis reveals distinct topological regimes, Sgr A* retains both tangential and radial critical curves, while M87* may show only tangential critical curves due to its larger mass. This topological difference provides a clear observational signature for future observations.
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Cosmology and Nongalactic Astrophysics
Say Hello, Wave Goodbye: Gravitational Waves from Hyperbolic PBH-SMBH Interactions
Laura Burn, Nelson Christensen and Richard Easther
Primordial black holes (PBHs) formed in the early Universe remain a viable dark matter candidate. Since dark matter is expected to be concentrated toward galactic centres, a significant population of PBHs would reside near a supermassive black hole (SMBH), providing a promising environment for gravitational wave emission. We consider PBHs with masses from $10^{-15}$ to $10$ solar masses on
hyperbolic trajectories past an SMBH, that produce bursts of gravitational radiation during periastron passage. Sagittarius A* is an obvious location for these events, but we show that both M31* and M87* would generate similar signals, albeit at lower frequencies. We assess the detectability of both individual bursts and "popcorn" backgrounds, relative to LISA and the proposed $\mu$Ares mission. Comparing these results to plausible central
halo densities, we find that unbound PBHs are unlikely to yield detectable signals.
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