LCDM Research Articles

The satellite galaxy plane of NGC 4490 in light of ΛCDM

Context. The system of galaxies around NGC 4490 was recently highlighted to display a flattened, kinematically correlated structure reminiscent of planes of satellite galaxies around other hosts. Aims. Since known satellite planes are in tension with expectations from cosmological simulations in the Λ cold dark matter (ΛCDM) model, we aim to quantitatively assess for the first time the tension posed by the NGC 4490 system. Methods. We measured the on-sky flattening as the major-to-minor axis ratio b/a of the satellite distribution and their line-of-sight kinematic correlation. Analogs to the system were selected in the TNG50 simulation and their flattening and correlation were similarly measured. Results. We confirm the strong kinematic coherence of all 12 observed satellite objects with available line-of-sight velocities (of 14 in total): the northern ones approach and the southern ones recede relative to the host. The spatial distribution of all 14 objects is substantially flattened with b/a = 0.38 (0.26 considering only the 12 objects with available velocities). Such extreme arrangements are rare in the ΛCDM simulation, at a level of 0.21 to 0.35%. This fraction of analogs would drop further if at least one of the two satellite objects without velocities is confirmed to follow the kinematic trend, and would become zero if both are rejected as non-members. We also identify a likely galaxy pair in the observed system, and find a similar pair in the best-matching simulated analog. Conclusions. Our measurements establish NGC 4490 as another strong example of a satellite plane in the Local Volume. This emphasizes that planes of satellites are a more general issue faced by ΛCDM also beyond the Local Group. The tension with typical systems drawn from simulations suggests that the observed one requires a specific formation scenario, potentially connected to the larger-scale galaxy alignment in its vicinity. The presence of galaxy pairs in the observed and a simulated system hints at the importance such groupings may have to understand satellite planes.

Reconstructing the matter power spectrum with future cosmic shear surveys

ABSTRACT Analyses of cosmic shear typically condense weak lensing information over a range of scales to a single cosmological parameter, $S_8$. This paper presents a method to extract more information from Stage IV cosmic shear measurements by directly reconstructing the matter power spectrum from linear to non-linear scales. We demonstrate that cosmic shear surveys will be sensitive to the shape of the matter power spectrum on non-linear scales. We show that it should be possible to distinguish between different models of baryonic feedback and we investigate the impact of intrinsic alignments and observational systematics on forecasted constraints. In addition to providing important information on galaxy formation, power spectrum reconstruction should provide a definitive answer to the question of whether weak lensing measurements of $S_8$ on linear scales are consistent with the Planck Lambda cold dark matter cosmology. In addition, power spectrum reconstruction may lead to new discoveries on the composition of the dark sector.

Semi-symmetric metric gravity: From the Friedmann–Schouten geometry with torsion to dynamical dark energy models

In this paper, we develop a geometric generalization of General Relativity based on the semi-symmetric metric connection introduced by Friedmann and Schouten in 1924. Although the mathematical properties of this connection, which allows for torsion, have been extensively studied, its physical implications remain underexplored. We provide a detailed exposition of the differential geometric aspects of semi-symmetric connections and formulate the corresponding field equations induced by the specific form of torsion we are investigating. We consider the cosmological applications of the theory by deriving the generalized Friedmann equations in a flat, homogeneous and isotropic geometry. The Friedmann equations also include some supplementary terms as compared to their general relativistic counterparts, which can be interpreted as a geometric type dark energy. To evaluate the proposed theory, we consider three cosmological models — the first with constant effective density and pressure, the second with the dark energy satisfying a linear equation of state, and a third one with a polytropic equation of state. We also compare the predictions of the semi-symmetric metric gravitational theory with the observational data for the Hubble function, and with the predictions of the ΛCDM model. Our findings indicate that the semi-symmetric metric cosmological models give a good description of the observational data, and for certain values of the model parameters, they can reproduce almost exactly the predictions of the ΛCDM paradigm. Consequently, Friedmann’s initially proposed geometry emerges as a credible alternative to standard general relativity, in which dark energy has a purely geometric origin.

Constraining modified gravity scenarios with the 6dFGS and SDSS galaxy peculiar velocity data sets

ABSTRACT The detailed nature of dark energy remains a mystery, leaving the possibility that its effects might be explained by changes to the laws of gravity on large scales. The peculiar velocities of galaxies directly trace the strength of gravity on cosmic scales and provide a means to further constrain such models. We generate constraints on different scenarios of gravitational physics by measuring peculiar velocity (PV) and galaxy clustering two-point correlations, using redshifts and distances from the 6-degree Field Galaxy Survey and the Sloan Digital Sky Survey PV samples, and fitting them against models characteristic of different cosmologies. Our best-fitting results are all found to be in statistical agreement with general relativity, in which context we measure the low-redshift growth of structure to be $f\sigma _8 = 0.329^{+0.081}_{-0.083}$, consistent with the prediction of the standard Lambda cold dark matter model. We also fit the modified gravity scenarios of Dvali–Gabadadze–Porrati and a Hu–Sawicki model of $f(R)$ gravity, finding the $2\sigma$ limit of their characteristic parameters to be $r_{\rm c}H_0/c\gt 6.987$ and $-\log _{10}(|f_{R0}|)\gt 4.703$, respectively. These constraints are comparable to other literature values, though it should be noted that they are significantly affected by the prior adopted for their characteristic parameters. When applied to much larger upcoming PV surveys such as DESI, this method will place rapidly improving constraints on modified gravity models of cosmic expansion and growth.

Probing flavor violation and baryogenesis via primordial gravitational waves

We show that observations of primordial gravitational waves of inflationary origin can shed light into the scale of flavor violation in a flavon model which also explains the mass hierarchy of fermions. The energy density stored in oscillations of the flavon field around the minimum of its potential redshifts as matter and is expected to dominate over radiation in the early universe. At the same time, the evolution of primordial gravitational waves acts as bookkeeping to understand the expansion history of the universe. Importantly, the gravitational wave spectrum is different if there is an early flavon dominated era compared to radiation domination expected from a standard cosmological model and this spectrum gets damped by the entropy released in flavon decays, determined by the mass of the flavon field mS and new scale of flavor violation ΛFV. We derive analytical expressions of the frequency above which the spectrum is damped, as-well-as the amount of damping, in terms of mS and ΛFV. We show that the damping of the gravitational wave spectrum would be detectable at BBO, DECIGO, U-DECIGO, μ−ARES, LISA, CE and ET detectors for ΛFV = 105−10 GeV and mS = OTeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O}\\left(\ extrm{TeV}\\right) $$\\end{document}. Furthermore, the flavon decays can source the baryon asymmetry of the universe. We identify the mS – ΛFV parameter space where the observed baryon asymmetry η ~ 10−10 is produced and can be tested by gravitational wave detectors like LISA and ET. We also discuss our results in the context of the recently measured stochastic gravitational background signals by NANOGrav.

Testing cosmic anisotropy with Padé approximations and the latest Pantheon+ sample

Cosmography can be used to constrain the kinematics of the Universe in a model-independent way. In this work, we attempt to combine the Pad$ e $ approximations with the latest Pantheon+ sample to test the cosmological principle. Based on the Pad$ e $ approximations, we first applied cosmographic constraints to different-order polynomials including third-order (Pad$ e $), fourth-order (Pad$ e $), and fifth-order (Pad$ e $) ones. The statistical analyses show that the Pad$ e $ polynomial has the best performance. Its best fits are $H_ $ = 72.53pm 0.28 km s$^ $ Mpc$^ $, $q_ $, and $j_ $. By further fixing $j_ $ = 1.00, it can be found that the Pad$ e $ polynomial can describe the Pantheon+ sample better than the regular Pad$ e $ polynomial and the usual cosmological models (including the Lambda CDM, $w$CDM, CPL, and $R_h$ = ct models). Based on the Pad$ e $ ($j_ $ = 1) polynomial and the hemisphere comparison method, we tested the cosmological principle and found the preferred directions of cosmic anisotropy, such as (l, b) = (304.6$^ circ circ $) and (311.1$^ circ circ $) for $q_ $ and $H_ $, respectively. These two directions are consistent with each other at a $1 confidence level, but the corresponding results of statistical isotropy analyses including isotropy and isotropy with real positions are quite different. The statistical significance of $ is stronger than that of $q_ $; that is, 4.75sigma and 4.39sigma for isotropy and isotropy with real positions, respectively. Reanalysis with fixed $q_ = -0.55$ (corresponds to $ m $ = 0.30) gives similar results. Overall, our model-independent results provide clear indications of a possible cosmic anisotropy, which must be taken seriously. Further testing is needed to better understand this signal.

Unveiling the evolution of rotating black holes in loop quantum cosmology

In this work, we aim to discuss about the evolution of rotating black holes (RBHs) within the context of loop quantum cosmology. Here, the main part of our research work focuses on the impacts of angular momentum based rotating parameter and accretion efficiency on the lifetime of RBHs. Our study reveals that accretion of dark energy would not significantly affect the evolution of RBHs, however higher value of rotating parameter could slightly delay the evaporation times of RBHs. Our analysis also depicts that the maximum value of rotating parameter for evolution of any RBH is 10-8Mi2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{-8}M_i^2$$\\end{document}, where Mi\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$M_i$$\\end{document} is the formation mass of RBH. Moreover, from our calculation we found that the maximum mass of a presently existing supermassive black hole would be 1048g\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{48}\ ext {g}$$\\end{document}, if it undergoes rotation. Also from astrophysical constraint analysis, we found that there is a greater tendency for formation of black holes in loop quantum cosmology than standard model of cosmology.

ΛCDM Tensions: Localising Missing Physics through Consistency Checks

ΛCDM tensions are by definition model-dependent; one sees anomalies through the prism of ΛCDM. Thus, progress towards tension resolution necessitates checking the consistency of the ΛCDM model to localise missing physics either in redshift or scale. Since the universe is dynamical and redshift is a proxy for time, it is imperative to first perform consistency checks involving redshift, then consistency checks involving scale as the next steps to settle the “systematics versus new physics” debate and foster informed model building. We present a review of the hierarchy of assumptions underlying the ΛCDM cosmological model and comment on whether relaxing them can address the tensions. We focus on the lowest lying fruit of identifying missing physics through the identification of redshift-dependent ΛCDM model fitting parameters. We highlight the recent progress made on S8:=σ8Ωm/0.3 tension and elucidate how similar progress can be made on H0 tension. Our discussions indicate that H0 tension, equivalently a redshift-dependent H0, and a redshift-dependent S8 imply a problem with the background ΛCDM cosmology.

Bulk viscous cosmological model in [formula omitted] modified gravity

This article explores the impact of bulk viscosity on understanding the universe’s accelerated expansion within the context of modified f(T,T) gravity, which is an extension of the f(T) gravitational theory, allowing a broad coupling between the energy–momentum scalar T and the torsion scalar T. We consider two f(T,T) functions, specifically f(T,T)=αT+βT and f(T,T)=α−T+βT, where α and β are arbitrary constants, along with the fluid part incorporating the coefficient of bulk viscosity ζ=ζ0>0. We calculate the analytical solutions of the corresponding field equations for a flat FLRW environment, and then we constrain the free parameters of the obtained solution using CC, Pantheon+, and the CC+Pantheon+ samples. We perform the Bayesian statistical analysis to estimate the posterior probability utilizing the likelihood function and the MCMC random sampling technique. Further, to assess the effectiveness of our MCMC analysis, we estimate the corresponding AIC and BIC values, and we find that there is strong evidence supporting the assumed viscous modified gravity models for all three data sets. Also, we find that the linear model precisely mimics the ΛCDM model. We also investigate the evolutionary behavior of some prominent cosmological parameters. We observe that the effective equation of state parameter for both models predict the accelerating behavior of the cosmic expansion phase. In addition, from the statefinder test, we find that the parameters of the considered MOG models favor the quintessence-type behavior. Further, we observe that the behavior of Om(z) curves corresponding to both models represent a consistent negative slope across the entire domain. We infer that our cosmological setting utilizing f(T,T) gravity models with the viscous matter fluid embodies quintessence-like behavior and can successfully describe the late-time scenario.

Detecting ultralight dark matter gravitationally with laser interferometers in space

Ultralight dark matter (ULDM) is one of the leading well-motivated dark matter candidates, predicted in many theories beyond the standard model of particle physics and cosmology. There has been increasing interest in searching for ULDM in physical and astronomical experiments, mostly assuming there are additional interactions other than gravity between ULDM and normal matter. Here we demonstrate that even if ULDM has only gravitational interaction, it shall induce gravitational perturbations in solar system that may be large enough to cause detectable signals in future gravitational-wave (GW) laser interferometers in space. We investigate the sensitivities of Michelson time-delay interferometer to ULDM of various spins, and show vector ULDM with mass m≲10−18 eV can be probed by space-based GW detectors aiming at μHz frequencies. Our findings exhibit that GW detectors may directly probe ULDM in some mass ranges that otherwise are challenging to examine. Published by the American Physical Society 2024

Late-time constraints on barotropic fluid cosmology

We investigate the cosmological implications of the Friedmann-Robertson-Walker (FRW) model having a flat-spatial section with barotropic fluid. We examine the resulting cosmological scenario obtained by solving the continuity equation. The model may yield the accelerating universe expansion from the transition of decelerated phase, subjected to the best fit values. We confront the cosmological model with the recent observational data, namely the Observational Hubble Data (OHD) and Supernovae type Ia (SN Ia) data. The model exhibits good agreement with these observational data sets. For the best fit values of the model parameters, the universe approaches to the Λ cold dark matter (ΛCDM) model in the distant future. Energy conditions except strong energy conditions are satisfied in the model. Analysis of the equation of state (EoS) parameter and statefinder diagnostic highlight that the phantom scenario does not arise for the best fit values. The universe is free from the finite-time future singularities in the model.

Screened Scalar Fields in the Laboratory and the Solar System

The last few decades have provided abundant evidence for physics beyond the two standard models of particle physics and cosmology. As is now known, the by far largest part of our universe’s matter/energy content lies in the ‘dark’, and consists of dark energy and dark matter. Despite intensive efforts on the experimental as well as the theoretical side, the origins of both are still completely unknown. Screened scalar fields have been hypothesized as potential candidates for dark energy or dark matter. Among these, some of the most prominent models are the chameleon, symmetron, and environment-dependent dilaton. In this article, we present a summary containing the most recent experimental constraints on the parameters of these three models. For this, experimental results have been employed from the qBounce collaboration, neutron interferometry, and Lunar Laser Ranging (LLR), among others. In addition, constraints are forecast for the Casimir and Non-Newtonian force Experiment (Cannex). Combining these results with previous ones, this article collects the most up-to-date constraints on the three considered screened scalar field models.

Extended uncertainty principle: A deeper insight into the Hubble tension?

The standard cosmological model, known as the ΛCDM model, has been successful in many respects, but it has some significant discrepancies, some of which have not been resolved yet. In measuring the Hubble-Lemaître parameter, there is an apparent discrepancy which is known as the Hubble tension, defined as differences in values of this parameter measured by the Type Ia Supernovae (SNeIa) data (a model-independent method) and by the Cosmic Microwave Background (CMB) radiation maps (a model-dependent method). Although many potential solutions have been proposed, the issue still remains unresolved. Recently, it was observed that the Hubble tension can be due to the concept of uncertainty in measuring cosmological parameters at large distance scales through applying the Heisenberg Uncertainty Principle (HUP) in cosmological setups. Extending this pioneering idea, in the present study we plan to incorporate the Extended Uncertainty Principle (EUP) containing a minimal fundamental measurable momentum (or equivalently, a maximal fundamental measurable length) as a candidate setup for describing large-scale effects of Quantum Gravity (QG) to address the Hubble tension and constrain the EUP length scale. In this regard, by finding a relevant formula for the effective photon rest mass in terms of the present-time value of the Hubble-Lemaître parameter, we see that discrepancies in the value of photon rest mass associated with the Hubble-Lemaître parameter values estimated from model-independent and model-dependent methods perhaps is the cause of Hubble tension. We show explicitly that the presence of a non-zero minimal uncertainty in momentum (or non-zero maximal uncertainty in position) measurements as a consequence of the large distance quantum gravity effect addresses the Hubble tension satisfactorily without having to invoke new physics. Moreover, we use the formula for the effective photon rest mass to find some relevant lower bounds on the EUP length scale.

Constraining holographic dark energy and analyzing cosmological tensions

We investigate cosmological constraints on the holographic dark energy (HDE) using the state-of-the-art cosmological datasets: Planck CMB angular power spectra and weak lensing power spectra, Atacama Cosmology Telescope (ACT) temperature power spectra, baryon acoustic oscillation (BAO) and redshift-space distortion (RSD) measurements from six-degree-field galaxy survey and Sloan Digital Sky Survey (DR12 & DR16) and the Cepheids-Supernovae measurement from SH0ES team (R22). We also examine the HDE model and ΛCDM with and without Neff (effective number of relativistic species) being treated as a free parameter. We find that the HDE model can relieve the tensions of H0 and S8 to certain degrees. With “Planck+ACT+BAO+RSD” datasets, the constraints are H0=69.70±1.39km s−1Mpc−1 and S8=0.823±0.011 in HDE model, which brings down the Hubble tension down to 1.92σ confidence level (C.L.) and the S8 tension to (1−2)σ C.L. By adding the R22 data, their values are improved as H0=71.86±0.93km s−1Mpc−1 and S8=0.813±0.010, which further brings the Hubble tension down to 0.85σ C.L. and relieves the S8 tension. We also quantify the goodness-of-fit of different models with Akaike information criterion (AIC) and Bayesian information criterion (BIC), and find that the HDE agrees with the observational data better than the ΛCDM and other extended models (treating Neff as free for fitting).

Satellite group infall into the Milky Way: Exploring the Crater-Leo case with new HST proper motions

Context. Within Λ cold dark matter (ΛCDM) simulations, Milky Way-like galaxies accrete some of their satellite galaxies in groups of 3–5 members rather than individually, and this has been suggested as a possible mechanism driving the formation of satellite planes. Objects accreted in groups are expected to share similar specific total energy and angular momentum, and to also have identical orbital planes and directions. Aims. Looking at observatio ns of Milky Way satellites, the dwarf galaxies Leo II, IV, V, and Crater II, and the star cluster Crater 1 were proposed to be a vestige of group infall. The suggested ‘Crater-Leo group’ shows a coherent distance gradient and all these objects align along a great circle on the sky. We used proper motion data to investigate whether the phase-space distribution of the members of the proposed group are indeed consistent with group infall. Methods. To further investigate this possibility, we used Gaia Data Release 3 (DR3) and new Hubble Space Telescope (HST) proper motions – namely, (μα*, μδ) = (−0.1921 ± 0.0514, −0.0686 ± 0.0523) mas yr−1 for Leo IV and (μα*, μδ) = (0.1186 ± 0.1943, −0.1183 ± 0.1704) mas yr−1 for Leo V – to derive accurate orbital properties for the proposed group objects. In addition, we explored other possible members of this putative association. Results. Leo II, Leo IV, and Crater 1 show orbital properties consistent with those we predict from assuming group infall. However, our results suggest that Crater II was not accreted with the rest of the objects. If confirmed with increasingly accurate proper motions in the future, the Crater-Leo objects would appear to constitute the first identified case of a cosmologically expected, typical group infall event, as opposed to the highly hierarchical Magellanic Cloud system.

The anomaly of the CMB power with the latest Planck data

The lack of power anomaly is an unexpected feature observed at large angular scales in the maps of Cosmic Microwave Background (CMB) produced by the COBE, WMAP and Planck satellites. This signature, which consists in a missing of power with respect to that predicted by the ΛCDM model, might hint at a new cosmological phase before the standard inflationary era.The main point of this paper is taking into account the latest Planck polarisation data to investigate how the CMB polarisation improves the understanding of this feature. With this aim, we apply to the latest Planck data, both PR3 (2018) and PR4 (2020) releases, a new class of estimators capable of evaluating this anomaly by considering temperature and polarisation data both separately and in a jointly way. This is the first time that the PR4 dataset has been used to study this anomaly. To critically evaluate this feature, taking into account the residuals of known systematic effects present in the Planck datasets, we analyse the cleaned CMB maps using different combinations of sky masks, harmonic range and binning on the CMB multipoles.Our analysis shows that the estimator based only on temperature data confirms the presence of a lack of power with a lower-tail-probability (LTP), depending on the component separation method, ≤ 0.33% and ≤ 1.76% for PR3 and PR4, respectively. To our knowledge, the LTP≤ 0.33% for the PR3 dataset is the lowest one present in the literature obtained from Planck 2018 data, considering the Planck confidence mask. We find significant differences between these two datasets when polarisation is taken into account most likely due to a different level of systematics. Especially, the analysis with PR3 data, unlike that with PR4, seems to point towards a lack of power at large scales also for polarisation.Moreover, we also show that for the PR3 dataset the inclusion of the subdominant polarisation information provides estimates that are less likely accepted in a ΛCDM cosmological model than the only-temperature analysis over the entire harmonic-range considered. In particular, at ℓmax = 26, we found that no simulation has a value as low as the data for all the pipelines.

Neutrino Mass Constraint from an Implicit Likelihood Analysis of BOSS Voids

Cosmic voids identified in the spatial distribution of galaxies provide complementary information to two-point statistics. In particular, constraints on the neutrino mass sum, ∑m ν , promise to benefit from the inclusion of void statistics. We perform inference on the CMASS Northern Galactic Cap sample of the third-generation Sloan Digital Sky Survey/Baryon Oscillation Spectroscopic Survey (BOSS) with the aim of constraining ∑m ν . We utilize the void size function, the void–galaxy cross power spectrum, and the galaxy auto power spectrum. To extract constraints from these summary statistics we use a simulation-based approach, specifically implicit likelihood inference. We populate approximate gravity-only, particle-neutrino cosmological simulations with an expressive halo occupation distribution model. With a conservative scale cut of kmax=0.15hMpc−1 and a Planck-inspired Lambda cold dark matter prior, we find upper bounds on ∑m ν of 0.43 and 0.35 eV from the galaxy auto power spectrum and the full data vector, respectively (95% credible interval). Relaxing the scale cut to kmax=0.2hMpc−1 , we find 0.28 and 0.32 eV. Generally, void statistics appear to add modest but nonzero information beyond the auto power spectrum. We also substantiate the usual assumption that the void size function is Poisson distributed.

Dianoga SIDM: Galaxy cluster self-interacting dark matter simulations

Context. Self-interacting dark matter (SIDM) can tackle or alleviate small-scale issues within the cosmological standard model ΛCDM, and diverse flavours of SIDM can produce unique astrophysical predictions, resulting in different possible signatures which can be used to test these models with dedicated observations of galaxy clusters. Aims. This work aims to assess the impact of dark matter self-interactions on the properties of galaxy clusters. In particular, the goal is to study the angular dependence of the cross section by testing rare (large angle scattering) and frequent (small angle scattering) SIDM models with velocity-dependent cross sections. Methods. We re-simulated six galaxy cluster zoom-in initial conditions with a dark matter-only run and with full-physics set-up simulations that include a self-consistent treatment of baryon physics. We tested the dark matter-only setup and the full physics setup with the collisionless cold dark matter, rare self-interacting dark matter, and frequent self-interacting dark matter models. We then studied their matter density profiles as well as their subhalo population. Results. Our dark matter-only SIDM simulations agree with theoretical models, and when baryons are included in simulations, our SIDM models substantially increase the central density of galaxy cluster cores compared to full-physics simulations using collisionless dark matter. SIDM subhalo suppression in full-physics simulations is milder compared to the one found in the dark matter-only simulations because of the cuspier baryonic potential that prevents subhalo disruption. Moreover, SIDM with small-angle scattering significantly suppresses a larger number of subhaloes compared to large-angle scattering SIDM models. Additionally, SIDM models generate a broader range of subhalo concentration values, including a tail of more diffuse subhaloes in the outskirts of galaxy clusters and a population of more compact subhaloes in the cluster cores.

Apparent dark matter inspired by the Einstein equation of state

The purpose of this article is twofold. First, by means of Padmanabhan's proposal on the emergence nature of gravity, we recover the ΛCDM model and the effect of the dark matter in the context of cosmology. Toward this goal, we use the key idea of Padmanabhan that states cosmic space emerges as the cosmic time progresses and links the emergence of space to the difference between the number of degrees of freedom on the boundary and in the bulk. Interestingly enough, we show that the effect of the cold dark matter in the cosmological setup can be understood by assuming an interaction between the numbers of degrees of freedom in the bulk. In the second part, we follow Jacobson's argument and obtain the modified Einstein field equations with additional dark matter component emerging due to the interaction term between dark energy and baryonic matter related by , where α is a coupling constant. Finally, a correspondence with the Yukawa cosmology is pointed out, and the role of massive gravitons as a possibility in explaining the nature of the dark sector as well as the theoretical origin of the Modified Newtonian Dynamics (MOND) are addressed. We speculate that the interaction coupling α fundamentally measures the entanglement between the gravitons and matter fields and there exists a fundamental limitation in measuring the gravitons wavelength.

Accretion onto oscillating cosmic string loops

Cosmic string loops are non-linear density fluctuations which form in the early universe and could play an important role in explaining many phenomena which are in tension with the standard ΛCDM model. Hence, the accretion process onto cosmic string loops should be studied in detail. Most previous works view loops as point masses and ignore the impact of a finite loop size. In this work, we utilize the Zel'dovich approximation to calculate the non-linear mass sourced by a static extended loop with a time-averaged density profile derived from the trajectory of the loop oscillation, and compare the result with what is obtained for a point-mass source. We find that the finite size of a loop mainly affects the evolution of turnaround shells during the early stages of accretion, converging to the point mass result after a critical redshift, zc ( II)/( III). For zc ( II)/( III), the total accreted mass surrounding a loop is suppressed relative to the point mass case and has a growth rate proportional to (1+z)-3/2.As an immediate extension, we also qualitatively analyse the accretion onto moving point masses and onto moving extended loops. In addition to the reduction in the nonlinear mass, the loop finite size also changes the shape of the turnaround surface at early stages of accretion.