Search

We derive an analytic expression for the two-point correlation function in redshift space which (i) is nonlinear; (ii) is valid on the full sky, i.e. the distant-observer limit is not assumed; (iii) can account for the effect of magnification and evolution bias due to a non-uniform selection function; and (iv) respects the fact that observations are made on the past lightcone, so naturally yields unequal-time correlations. Our model is based on an exact treatment of the streaming model in the wide-angle regime. Within this general regime, we find that the redshift-space correlation function is essentially determined by a geometric average of its real-space counterpart. We show that the linear expression for the galaxy overdensity, accurate to subleading order, can be recovered from our nonlinear framework. This work is particularly relevant for the modeling of odd multipoles of the correlation function at small separations and low redshifts, where wide-angle effects, selection effects, and nonlinearities are expected to be equally important., 21 pages, 3 figures

We report new observations of the cool diffuse gas around 29, $2.3$9. MgII absorption kinematics are shifted from the systemic redshift of host galaxies with a median absolute velocity of 135 km/s and standard deviation of 85 km/s. The high kinematic offset and large radial separation ($R> 1.3 R_{200}$), suggest that five out of the seven MgII absorption systems are gravitationally not bound to the galaxies. In contrast, most cool circumgalactic media at $z4$., Comment: 21 pages, 12 figures, 2 tables, ApJ submitted

We derive predictions from state-of-the-art cosmological galaxy simulations for the spatial distribution of the hot circumgalactic medium (CGM, ${\rm [0.1-1]R_{200c}}$) through its emission lines in the X-ray soft band ($[0.3-1.3]$ keV). In particular, we compare IllustrisTNG, EAGLE, and SIMBA and focus on galaxies with stellar mass $10^{10-11.6}\, \MSUN$ at $z=0$. The three simulation models return significantly different surface brightness radial profiles of prominent emission lines from ionized metals such as OVII(f), OVIII, and FeXVII as a function of galaxy mass. Likewise, the three simulations predict varying azimuthal distributions of line emission with respect to the galactic stellar planes, with IllustrisTNG predicting the strongest angular modulation of CGM physical properties at radial range ${\gtrsim0.3-0.5\,R_{200c}}$. This anisotropic signal is more prominent for higher-energy lines, where it can manifest as X-ray eROSITA-like bubbles. Despite different models of stellar and supermassive black hole (SMBH) feedback, the three simulations consistently predict a dichotomy between star-forming and quiescent galaxies at the Milky-Way and Andromeda mass range, where the former are X-ray brighter than the latter. This is a signature of SMBH-driven outflows, which are responsible for quenching star formation. Finally, we explore the prospect of testing these predictions with a microcalorimeter-based X-ray mission concept with a large field-of-view. Such a mission would probe the extended hot CGM via soft X-ray line emission, determine the physical properties of the CGM, including temperature, from the measurement of line ratios, and provide critical constraints on the efficiency and impact of SMBH feedback on the CGM., 21 pages, 15 figures. Submitted to MNRAS and received a positive referee report

We derive exact and closed-form expressions for a large class of two-point and three-point inflation correlators with the tree-level exchange of a single massive particle. The intermediate massive particle is allowed to have arbitrary mass, spin, chemical potential, and arbitrary nonderivative or derivative couplings to external inflaton modes. We also allow the coupling coefficients to have arbitrary complex power dependences on the conformal time. Our results feature closed-form expressions involving only familiar special functions and without any infinite sums. This is achieved by an improved bootstrap method with a suitable change of variables. Our results cover a wide range of cosmological collider models and can be directly used for future phenomenological studies. Our results can also be used as basic building blocks for constructing more complicated inflation correlators., 41 pages

Observations of the millimeter sky contain valuable information on a number of signals, including the blackbody cosmic microwave background (CMB), Galactic emissions, and the Compton-$y$ distortion due to the thermal Sunyaev-Zel'dovich (tSZ) effect. Extracting new insight into cosmological and astrophysical questions often requires combining multi-wavelength observations to spectrally isolate one component. In this work, we present a new arcminute-resolution Compton-$y$ map, which traces out the line-of-sight-integrated electron pressure, as well as maps of the CMB in intensity and E-mode polarization, across a third of the sky (around 13,000 sq.~deg.). We produce these through a joint analysis of data from the Atacama Cosmology Telescope (ACT) Data Release 4 and 6 at frequencies of roughly 93, 148, and 225 GHz, together with data from the \textit{Planck} satellite at frequencies between 30 GHz and 545 GHz. We present detailed verification of an internal linear combination pipeline implemented in a needlet frame that allows us to efficiently suppress Galactic contamination and account for spatial variations in the ACT instrument noise. These maps provide a significant advance, in noise levels and resolution, over the existing \textit{Planck} component-separated maps and will enable a host of science goals including studies of cluster and galaxy astrophysics, inferences of the cosmic velocity field, primordial non-Gaussianity searches, and gravitational lensing reconstruction of the CMB., The Compton-y map and associated products will be made publicly available upon publication of the paper. The CMB T and E mode maps will be made available when the DR6 maps are made public

The recently released data by pulsar timing array (PTA) collaborations present strong evidence for a stochastic signal consistent with a gravitational-wave background. Assuming this signal originates from scalar-induced gravitational waves, we jointly use the PTA data from the NANOGrav 15-yr data set, PPTA DR3, and PPTA DR2 to probe the small-scale non-Gaussianity. We put the first-ever constraint on the non-Gaussianity parameter, finding $|F_\mathrm{NL}|\lesssim 20$ for a lognormal power spectrum of the curvature perturbations. Furthermore, we obtain $-20 \lesssim F_\mathrm{NL}\lesssim -0.1$ to prevent excessive production of primordial black holes. Our findings pave the way to constrain inflation models with PTA data. Moreover, the multi-band observations with the space-borne gravitational-wave detectors, such as LISA/Taiji/TianQin, will provide a complementary investigation of non-Gaussianity., 8 pages, 2 figures, 1 table

We study the vacuum zero point energy associated to a scalar field with an arbitrary mass and conformal coupling in a dS background. Employing dimensional regularization scheme, we calculate the regularized zero point energy density, pressure and the trace of the energy momentum tensor. It is shown that the classical relation $\langle T \rangle =-4 \langle \rho \rangle$ for the vacuum stress energy tensor receives anomalous quantum correction which depends on the mass and the conformal coupling while the relation $\langle \rho \rangle = - \langle P \rangle$ does hold. We calculate the density contrast associated to the vacuum zero point energy and show that $\delta \rho \sim \langle \rho \rangle$ indicating an inhomogeneous and non-perturbative distribution of the zero point energy. Finally, we calculate the skewness associated to the distribution of the zero point energy and pressure and show that they are highly non-Gaussian., Comment: 23 pages

The number density of extragalactic 21-cm radio sources as a function of their spectral line-widths -- the HI width function (HIWF) -- is a tracer of the dark matter halo mass function. The ALFALFA 21-cm survey measured the HIWF in northern and southern Galactic fields finding a systematically higher number density in the north; an asymmetry which is in tension with $\Lambda$ cold dark matter models which predicts the HIWF should be identical everywhere if sampled in sufficiently large volumes. We use the Sibelius-DARK N-body simulation and semi-analytical galaxy formation model GALFORM to create mock ALFALFA surveys to investigate survey systematics. We find the asymmetry has two origins: the sensitivity of the survey is different in the two fields, and the algorithm used for completeness corrections does not fully account for biases arising from spatial galaxy clustering. Once survey systematics are corrected, cosmological models can be tested against the HIWF., Comment: 4 pages, 2 figures. Accepted contribution to the proceedings for Dynamical Masses of Local Group Galaxies: IAU Symposium 379

We use the full-mission $\textit{Planck}$ PR4 data to construct maps of the thermal Sunyaev$--$Zel'dovich effect (Compton-$y$ parameter) in our Universe. To do so, we implement a custom needlet internal linear combination (NILC) pipeline in a Python package, $\texttt{pyilc}$, which we make publicly available. We publicly release our Compton-$y$ maps, which we construct using various constrained ILC (``deprojection'') options in order to minimize contamination from the cosmic infrared background (CIB) in the reconstructed signal. In particular, we use a moment-based deprojection which minimizes sensitivity to the assumed frequency dependence of the CIB. Our code $\texttt{pyilc}$ performs needlet or harmonic ILC on mm-wave sky maps in a flexible manner, with options to deproject various components on all or some scales. We validate our maps and compare them to the official $\textit{Planck}$ 2015 $y$-map, finding that we obtain consistent results on large scales and 10-20$\%$ lower noise on small scales. We expect that these maps will be useful for many auto- and cross-correlation analyses; in a companion paper, we use them to measure the tSZ -- CMB lensing cross-correlation. We anticipate that $\texttt{pyilc}$ will be useful both for data analysis and for pipeline validation on simulations to understand the propagation of foreground components through a full NILC pipeline., 28 pages, 15 figures. Public maps and other data products are available at https://users.flatironinstitute.org/~fmccarthy/ymaps_PR4_McCH23/ ; public code is available at https://github.com/jcolinhill/pyilc

We present the operating principle and the first observing run of a novel kind of direct detector for axions and axion-like particles in the galactic halo. Our experiment is sensitive to the polarisation rotation of linearly polarised laser light induced by an axion field, and the first detector of its kind collecting science data. We discuss our current peak sensitivity of $1.44\times 10^{-10}$ GeV$^{-1}$ (95 % confidence level) to the axion-photon coupling strength in the axion mass range of 1.97-2.01 neV which is, for instance, motivated by supersymmetric grand-unified theories. We also report on effects that arise in our high-finesse in-vacuum cavity at unprecedented optical continuous-wave intensity. Our detector already belongs to the most sensitive direct searches within its measurement band, and our first results pave the way towards surpassing the current sensitivity limits in the mass range from $10^{-8}$ eV down to $10^{-16}$ eV via quantum-enhanced laser interferometry.

We explore the possibility of using superfluid helium for direct detection of sub-GeV dark matter (DM). We discuss the relevant phenomenology resulting from the scattering of an incident dark matter particle on a Helium nucleus. Rather than directly exciting quasi-particles, DM in this mass range will interact with a single He atom, triggering an atomic cascade which eventually also includes emission and thermalization of quasi-particles. We present in detail the analytical framework needed for modeling these processes and determining the resulting flux of quasi-particles. We propose a novel method for detecting this flux with modern force-sensitive devices, such as nanoelectro-mechanical system (NEMS) oscillators, and derive the sensitivity projections for a generic sub-GeV DM detection experiment using such sensors., 28 pages, 12 figures

Quasars experiencing strong lensing offer unique viewpoints on subjects like the cosmic expansion rate, the dark matter profile within the foreground deflectors, and the quasar host galaxies. Unfortunately, identifying them in astronomical images is challenging since they are overwhelmed by the abundance of non-lenses. To address this, we have developed a novel approach by ensembling cutting-edge convolutional networks (CNNs) -- i.e., ResNet, Inception, NASNet, MobileNet, EfficientNet, and RegNet -- along with vision transformers (ViTs) trained on realistic galaxy-quasar lens simulations based on the Hyper Suprime-Cam (HSC) multiband images. While the individual model exhibits remarkable performance when evaluated against the test dataset, achieving an area under the receiver operating characteristic curve of $>$97.4% and a median false positive rate of 3.1%, it struggles to generalize in real data, indicated by numerous spurious sources picked by each classifier. A significant improvement is achieved by averaging these CNNs and ViTs, resulting in the impurities being downsized by factors up to 40. Subsequently, combining the HSC images with the UKIRT, VISTA, and unWISE data, we retrieve approximately 60 million sources as parent samples and reduce this to 892,609 after employing a photometry preselection to discover $z>1.5$ lensed quasars with Einstein radii of $θ_\mathrm{E}, Submitted to the Astronomy & Astrophysics journal. 25 pages, 11 figures, and 3 tables. We welcome comments from the reader

The hyperbolic encounters of two massive objects are characterized by the emission of a gravitational wave burst, with most of the energy released during the closest approach (near the periastron). The detection of such events, different from the well-known inspiral emission, would be an interesting discovery and provide complementary information to observations of binary mergers of black holes and neutron stars in the observable Universe, shedding light, for instance, on the clustering properties of black holes and providing valuable hints on their formation scenario. Here, we analyse the dynamics of such phenomena in the simplest case where two compact objects follow unbound/hyperbolic orbits. Moreover, we explore the effects of orbital precession on the gravitational wave emission, since the precession encodes certain general relativistic effects between two bodies. We also provide templates for the strain of gravitational waves and the power spectrum for the emission, and analytical expressions for the memory effect associated with such signals., 12 pages, 9 figures, comments welcome

Gravitational waves emitted from stellar binary black hole (sBBH) mergers can be gravitationally lensed by intervening galaxies and detected by future ground-based detectors. A large amount of effort has been put into the estimation of the detection rate of lensed sBBH originating from the evolution of massive binary stars (EMBS channel). However, sBBHs produced by the dynamical interaction in dense clusters (dynamical channel) may also be dominant in our universe and their intrinsic distribution of physical properties can be significantly different from those produced by massive stars, especially mass and redshift distribution. In this paper, we investigate the event rate of lensed sBBHs produced via dynamical channel by Monte Carlo simulations and the number is $16_{-12}^{+4.7} $ $\rm yr^{-1}$ for the Einstein telescope and $24_{-17}^{+6.8}$ $ \rm yr^{-1}$ for Cosmic Explorer, of which the median is about $\sim 2$ times the rate of sBBHs originated from EMBS channel (calibrated by the local merger rate density estimated for the dynamical and the EMBS channel, i.e., $\sim 14_{-10}^{+4.0}$ and $19_{-3.0}^{+42} \rm Gpc^{-3}yr^{-1}$ respectively). Therefore, one may constrain the fraction of both EMBS and dynamical channels through the comparison of the predicted and observed number of lensed sBBH events statistically., 9 pages, 4 Figures, Astrophysical Journal in Press

Motivated by the recent release of new results from five different pulsar timing array (PTA) experiments claiming to have found compelling evidence for primordial gravitational waves (GW) at nano-Hz frequencies, we study the consequences for two popular beyond the Standard Model (SM) framework, where such nano-Hz GW can arise due to annihilating domain walls (DW). Minimal framework of Dirac leptogenesis, as well as left-right symmetric model (LRSM) can lead to formation of DW due to spontaneous breaking of $Z_2$ symmetry. Considering the NANOGrav 15 yr data, we show that the scale of Dirac leptogenesis should be above $10^7$ GeV for conservative choices of Dirac Yukawa couplings with fine-tuning at the level of the SM. The scale of minimal LRSM is found to be more constrained $M_{\rm LR} \sim 10^6$ GeV in order to fit the NANOGrav 15 yr data., 6 pages, 4 figures, 1 table

Motivated by the recent release of new results from five different pulsar timing array (PTA) experiments claiming to have found compelling evidence for primordial gravitational waves (GW) at nano-Hz frequencies, we consider the prospects of generating such a signal from inflationary blue-tilted tensor power spectrum in a specific dark matter (DM) scenario dubbed as \textit{Miracle-less WIMP}. While \textit{Miracle-less WIMP}, due to insufficient interaction rate with the standard bath gets thermally overproduced, inflationary blue-tilted gravitational waves (BGW) leads to conflict with cosmological observations if solely responsible for the PTA events. Both these problems are circumvented with late entropy dilution bringing DM abundance within limits while creating a doubly peaked feature of BGW. The blue-tilted part of one of these peaks can fit NANOGrav 15 yr data at $1\sigma$ level. The particle physics setup used here for illustration namely, the gauged $U(1)_{B-L}$ model, naturally leads to \textit{Miracle-less WIMP} and long-lived diluter for entropy dilution while also having GW complementarity due to cosmic strings., Comment: 6 pages, 1 captioned figure

We explore possible signatures of the interaction between dark matter (DM) and massive neutrinos during the post-reionization epoch. Using both Fisher matrix forecast analysis and Markov Chain Monte-Carlo (MCMC) simulation, we conduct a thorough investigation of the constraints and imprints of the scenario on the upcoming post-reionization and galaxy surveys. Our investigation focuses on two key parameters: the strength of the DM-massive neutrino interaction ($u$) and the total neutrino mass ($M_{\rm tot}$), on top of the usual 6 cosmological parameters. We utilize future 21-cm intensity mapping, galaxy clustering as well as cosmic shear observations in order to investigate the possible constraints of these parameters in the future observations: Square Kilometre Array (SKA1 and SKA2) and Euclid, taking both conservative and realistic approaches. All these missions show promise in constraining both the parameters $u$ and $M_{\rm tot}$ by 3-4 orders compared to the current constraints from Planck18 (SKA2 performing the best among them). Although none of the missions help much in addressing the $H_0$ and $\sigma_8$ tensions for the present scenario, SKA2 constrains them better in conservative approach. We further perform a brief investigation of the prospects of some of the next generation Cosmic Microwave Background (CMB) missions in combinations with LSS experiments in improving the constraints. Our analysis reveals that both SKA2 and CMB-S4 + Euclid + SKA1 IM2 combination will put the strongest bounds on the model parameters., Comment: 13 pages, 10 figures

Primordial black holes may arise through ultra slow-roll inflation. In this work we study a toy model of ultra slow-roll inflation with a shallow dip. The ultra slow-roll stage enhances the curvature perturbations and thus the primordial scalar power spectrum. We analyze the features of the power spectrum numerically and analytically, and then give a rough estimate of the lower and upper bound of the enhancement. These large perturbations also produce second order gravitational waves, which are in the scope of future observations., 11pages, 7 figures

Significant evidence for a gravitational-wave background was reported by several pulsar-timing-array collaborations. By assuming that this signal is interpreted by the scalar-induced gravitational waves, we study physical implications of the observed signal for the nature of primordial curvature perturbations and primordial black holes. In particular, we explore the effects of primordial non-Gaussianity on the inferences of model parameters, and obtain the parameter region allowed by the observed signal, i.e., the primordial scalar spectral amplitude $A_S\sim10^{-2}-1$, the primordial non-Gaussian parameter $-10\lesssim f_{\mathrm{NL}} \lesssim 10$, and the mass of primordial black holes $m_{\mathrm{pbh}}\sim10^{-3}-0.1M_{\odot}$. We find that the non-Gaussianity suppressing the abundance of primordial black holes is preferred by the observed signal. We show that the anisotropies of scalar-induced gravitational waves are a powerful probe for measurements of the non-Gaussian parameter $f_{\mathrm{NL}}$, and conduct a complete analysis of the angular power spectrum in the nano-Hertz band. We expect that the Square Kilometre Array project has potentials to measure such anisotropies., 19 pages, 5 figures

Weak gravitational lensing is a powerful probe, which is used to constrain the standard cosmological model and its extensions. With the enhanced statistical precision of current and upcoming surveys, high-accuracy predictions for weak lensing statistics are needed to limit the impact of theoretical uncertainties on cosmological parameter constraints. For this purpose, we present a comparison of the theoretical predictions for the non-linear matter and weak lensing power spectra, based on the widely used fitting functions (mead and rev-halofit), emulators (EuclidEmulator, EuclidEmulator2, BaccoEmulator, and CosmicEmulator), and N-body simulations (PKDGRAV3). We consider the forecasted constraints on the ЛCDM and wCDM models from weak lensing for stage III and stage IV surveys. We study the relative bias on the constraints and their dependence on the assumed prescriptions. Assuming a ЛCDM cosmology, we find that the relative agreement on the S8 parameter is between 0.2 and 0.3σ for a stage III-like survey between the above predictors. For a stage IV-like survey the agreement becomes 1.4-3.0σ. In the wCDM scenario, we find broader S8 constraints, and agreements of 0.18-0.26σ and 0.7-1.7σ for stage III and stage IV surveys, respectively. The accuracies of the above predictors therefore appear adequate for stage III surveys, whereas the fitting functions would need improvements for future stage IV surveys. Furthermore, we find that, of the fitting functions, mead provides the best agreement with the emulators. We discuss the implication of these findings for the preparation of future weak lensing surveys, and the relative impact of theoretical uncertainties to other systematics., Monthly Notices of the Royal Astronomical Society, 522 (3), ISSN:0035-8711, ISSN:1365-2966

Decaying dark matter models generically modify the equation of state around the time of dark matter decay, and this in turn modifies the expansion rate of the Universe through the Friedmann equation. Thus, a priori, these models could solve or alleviate the Hubble tension, and depending on the lifetime of the dark matter, they can be classified as belonging to either the early- or late-time solutions. Moreover, decaying dark matter models can often be realized in particle physics models relatively easily. However, the implementations of these models in Einstein--Boltzmann solver codes are non-trivial, so not all incarnations have been tested. It is well known that models with very late decay of dark matter do not alleviate the Hubble tension, and in fact, cosmological data puts severe constraints on the lifetime of such dark matter scenarios. However, models in which a fraction of the dark matter decays to dark radiation at early times hold the possibility of modifying the effective equation of state around matter-radiation equality without affecting late-time cosmology. This scenario is therefore a simple realization of a possible early-time solution to the Hubble tension, and cosmological parameter estimation with current data in these models yields a value of $H_0 = 68.73^{+0.81}_{-1.3}$ at $68\%$ C.I.. This still leads to a $2.7\sigma$ Gaussian tension with the representative local value of $H_0 = 73.2 \pm 1.3$ km s$^{-1}$ Mpc$^{-1}$. Additional work is, however, required to test more complex decay scenarios, which could potentially prefer higher values of $H_0$ and provide a better solution to the Hubble tension., Comment: Invited chapter for the edited book Hubble Constant Tension (Eds. E. Di Valentino and D. Brout, Springer Singapore, expected in 2024)

We investigate the evolution of gravitational waves through discontinuous evolution (transition) of the Hubble expansion rate $H(z)$ at a sudden cosmological singularity, which may be due to a transition of the value of the gravitational constant. We find the evolution of the scale factor and the gravitational wave waveform through the singularity by imposing the proper boundary conditions. We also use existing cosmological data and mock data of future gravitational wave experiments (the ET) to impose current and anticipated constraints on the magnitude of such a transition. We show that mock data of the Einstein Telescope can reduce the uncertainties by up to a factor of three depending on the cosmological parameter considered., 40 pages, 15 Figures, 6 Tables. Published in Universe (Open Access: https://www.mdpi.com/2218-1997/9/7/317)!

In the realistic model of cosmic inflation the inflaton potential should be flat and stable under quantum corrections. It is natural to imagine that there is some symmetry behind and an idea of the inflaton as a Nambu-Goldstone boson of spontaneous breaking of some symmetry has been examined. We give a general formulation of this idea using the non-linear realization of Nambu-Goldstone boson in low-energy effective theory with some explicit symmetry breaking to generate non-trivial potential. The potential is naturally a simple function, typically the mass term of inflaton, and the scenario of "warm inflation" should necessarily be applied under the present observational constraints. We investigate the generation mechanism of necessary thermal dissipation term in inflaton field equation for "warm inflation" without large thermal corrections to inflaton potential. A simple numerical analysis is given to investigate the viability of this scenario., 11 pages

We present a method for obtaining unbiased signal estimates in the presence of a significant background, eliminating the need for a parametric model for the background itself. Our approach is based on a minimal set of conditions for observation and background estimators, which are typically satisfied in practical scenarios. To showcase the effectiveness of our method, we apply it to simulated data from the planned dielectric axion haloscope MADMAX., 9 pages, 3 figures, 1 table

In this work, we present novel analytical solutions for static and spherically symmetric wormhole geometries threaded by an anisotropic distribution of matter conformally coupled to a scalar ghost field. We explore the main features of the theory, such as the dynamics of the scalar field and matter throughout the wormhole, as well as the role played by the non-minimal coupling. Furthermore, coupled ghosts in the presence of a scalar potential are considered and traversability conditions are analysed within such geometrical scheme. More specifically, we find analytical solutions that although the energy density of the ghost is strictly negative, the energy density of matter may attain positive values., 12 pages, 9 figures

It has been shown that both scalar and tensor modes with non-Bunch-Davies initial states can enhance the amplitudes of the primordial bispectra compared to those with the Bunch-Davies state, especially for wavenumber modes in a flattened triangle configuration. However, in the case of the non-Bunch-Davies scalar modes, it has also been found that those enhancements in Fourier space are somewhat reduced in bispectra of cosmic microwave background (CMB) fluctuations. In this paper, we show that the enhancement resulting from the tensor modes is partially reduced to a degree differing from that of the scalar modes, which makes the non-Bunch-Davies effects unobservable in gravitational theories with the same quadratic and cubic operators of the tensor perturbations as general relativity. Furthermore, we present examples of gravitational theories yielding enhancements that would potentially be detected through CMB experiments., 12 pages

In applications of the conformal gravity theory it has been shown that a scale of order 105 Mpc due to large scale inhomogeneities such as clusters of galaxies is imprinted on the rotation curves of galaxies. Here we show that this same scale is imprinted on recombination era anisotropies in the cosmic microwave background. We revisit an analysis due to Mannheim and Horne, to show that in the conformal gravity theory the length scale of metric signals that originate in the primordial nucleosynthesis era at $10^{9\circ}$K can fill out the entire recombination era sky. Similarly, the length scale of acoustic signals that originate at $10^{13\circ}$K can also fill out the entire recombination era sky. We show that the amplitudes of metric fluctuations that originate in the nucleosynthesis era can grow by a factor of $10^{12}$ at recombination, and by a factor of $10^{18}$ at the current time. In addition we find that without any period of exponential expansion a length scale as small as $10^{-33}$ cm can grow to the size of the recombination sky if it begins to grow at a temperature of order $10^{33}$ degrees., Comment: 16 pages

Recently, NANOGrav has reported the observation of a stochastic gravitational wave background (SGWB) at nano-Hertz frequencies. String-wall networks and domain walls have been proposed as possible sources. To be cosmologically viable, these topological defect networks must annihilate before they dominate the energy budget of the universe, producing a SGWB. However, a part of the network can copiously produce primordial black holes that exceed current bounds. Performing a Bayesian analysis of pulsar timing residual datasets we find that the SGWB detected in PTA data is therefore hardly compatible with such an origin. This lends credibility to other interpretations, including supermassive black hole mergers, first order phase transitions, Nambu-Goto strings, and curvature-induced gravitational waves., 5 pages, 3 figures

The recent results from the Pulsar Timing Array (PTA) collaborations show the first evidence for the detection of a stochastic background of gravitational waves at the nHz frequencies. This discovery has profound implications for the physics of both the late and the early Universe. In fact, together with the possible interpretation in terms of super massive black hole binaries, many sources in the early Universe can provide viable explanations as well. In this paper, we study the gravitational wave background sourced by a network of axion-like-particle (ALP) domain walls at temperatures around the QCD crossover, where the QCD-induced potential provides the necessary bias to annihilate the network. Remarkably, this implies a peak amplitude at frequencies around the sensitivity range of PTAs. We extend previous analysis by taking into account the unavoidable friction on the network stemming from the topological coupling of the ALP to QCD in terms of gluon and pion reflection off the domain walls at high and low temperatures, respectively. We identify the regions of parameter space where the network annihilates in the scaling regime ensuring compatibility with the PTA results, as well as those where friction can be important and a more detailed study around the QCD crossover is required., 15 pages, 4 figures

Very recently, several pulsar timing array collaborations, including CPTA, EPTA, and NANOGrav, reported their results from searches for an isotropic stochastic gravitational wave background (SGWB), with each finding positive evidence for SGWB. In this work, we assessed the credibility of interpreting the Hellings-Downs correlated free-spectrum process of EPTA, PPTA, and NANOGrav as either the result of supermassive black hole binary mergers or various stochastic SGWB sources that originated in the early Universe, including first-order phase transitions, cosmic strings, domain walls, and large-amplitude curvature perturbations. Our observations show that the current new datasets do not display a strong preference for any specific SGWB source based on Bayesian analysis., 10 pages, 8 figures, 2 tables

We study the angular clustering of Quaia, a Gaia- and unWISE-based catalog of over a million quasars with an exceptionally well-defined selection function. With it, we derive cosmology constraints from the amplitude and growth of structure across cosmic time. We divide the sample into two redshift bins, centered at $z=1.0$ and $z=2.1$, and measure both overdensity auto-correlations and cross-correlations with maps of the Cosmic Microwave Background convergence measured by Planck. From these data, and including a prior from measurements of the baryon acoustic oscillations scale, we place constraints on the amplitude of the matter power spectrum $\sigma_8=0.766\pm 0.034$, and on the matter density parameter $\Omega_m=0.343^{+0.017}_{-0.019}$. These measurements are in reasonable agreement with \planck at the $\sim$ 1.4$\sigma$ level, and are found to be robust with respect to observational and theoretical uncertainties. We find that our slightly lower value of $\sigma_8$ is driven by the higher-redshift sample, which favours a low amplitude of matter fluctuations. We present plausible arguments showing that this could be driven by contamination of the CMB lensing map by high-redshift extragalactic foregrounds, which should also affect other cross-correlations with tracers of large-scale structure beyond $z\sim1.5$. Our constraints are competitive with those from state-of-the-art 3$\times$2-point analyses, but arise from a range of scales and redshifts that is highly complementary to those covered by cosmic shear data and most galaxy clustering samples. This, coupled with the unprecedented combination of volume and redshift precision achieved by Quaia allows us to break the usual degeneracy between $\Omega_m$ and $\sigma_8$., Comment: Submitted to JCAP, corrects links to public data release. The per-bin selection functions used in this analysis, and the complete set of power spectra, covariance, and associated metadata used in our fiducial analysis are publicly available at https://doi.org/10.5281/zenodo.8098635 . The public Quaia catalog can be found at https://doi.org/10.5281/zenodo.8060755

We apply the multi-tracer technique to test the possibility of improved constraints on the amplitude of local primordial non-Gaussianity, $f_{\mathrm{NL}}$, in the cosmic large-scale structure. A precise measurement of $f_{\mathrm{NL}}$ is difficult because the effects of non-Gaussianity mostly arise on the largest scales, which are heavily affected by the low statistical sampling commonly referred to as cosmic variance. The multi-tracer approach suppresses cosmic variance and we implement it by combining the information from next-generation galaxy surveys in the optical/near-infrared band and neutral hydrogen (HI) intensity mapping surveys in the radio band. High-redshift surveys enhance the precision on $f_{\mathrm{NL}}$, due to the larger available volume, and HI intensity mapping surveys can naturally reach high redshifts. In order to extend the redshift coverage of a galaxy survey, we consider different emission-line galaxy populations, focusing on the H$\alpha$ line at low redshift and on oxygen lines at higher redshift. By doing so, we cover a wide redshift range $1 \lesssim z \lesssim 4$. To assess the capability of our approach, we implement a synthetic-data analysis by means of Markov chain Monte Carlo sampling of the (cosmological+nuisance) parameter posterior, to evaluate the constraints on $f_{\mathrm{NL}}$ obtained in different survey configurations. We find significant improvements from the multi-tracer technique: the full data set leads to a precision of $\sigma(f_{\mathrm{NL}}) < 1$., Comment: 23 pages, 10 figures; to be submitted on JCAP; comments are welcome

The unimodular theory of gravity is an alternative perspective to traditional Einstein's general relativity and opens new possibilities for exploring its implications in cosmology. In this paper, we investigate the unimodular gravity (UG) with the latest cosmological data from the Pantheon sample of Type Ia supernovae (SN), Baryon Acoustic Oscillations (BAO), and the observational H(z) data from Differential Age method (DA). We consider a model consisting of a generalized cosmological constant with radiation and dark matter. The considered theory respects only unimodular coordinate transformations. We fit our model with low-redshift data from SN and DA and determine the value of parameter $\xi$ of the theory. We find the best-fit value of parameter $\xi =6.23 \pm 0.5$; which deviates from 6, for which the theory becomes the standard general theory of relativity. We further study the Hubble constant problem by combining the SN and DA data with BAO data. We observe deviation in the value of $H_0$ from the standard $\Lambda$CDM model. We obtain $H_0$ as $70.7 \pm 4.1 \ \mbox{Km s}^{-1} \mbox{Mpc} ^{-1}$ and $69.24 \pm 0.90 \ \mbox{Km s}^{-1} \mbox{Mpc} ^{-1}$ from supernovae data and BAO data, respectively in unimodular gravity. Combining the BAO data with SN+DA data set, we obtain $H_0$ as $70.57 \pm 0.56 \ \mbox{Km s}^{-1} \mbox{Mpc} ^{-1}$., Comment: 18 pages, 4 figures

We study the production of stochastic gravitational wave background from early dark energy (EDE) model. It is caused by resonant amplification of scalar field fluctuations, which easily takes place for typical EDE potential based on the string axion or $\alpha$-attractor model. The resultant spectrum of gravitational wave background is computed by performing 3D lattice simulations. We show that, specifically in some class of generalized $\alpha$-attractor EDE model, a significant amount of gravitational waves can be produced via tachyonic instability with a peak around femto-Hz frequency range. Models predicting such gravitational waves can be constrained by the cosmic microwave background observations., Comment: 15 pages, 5 figures

Pulsar Timing Arrays (PTAs) have reported evidence for a stochastic gravitational wave (GW) background at nHz frequencies, possibly originating in the early Universe. We show that the spectral shape of the low-frequency (causality) tail of GW signals sourced at temperatures around $T\gtrsim 1$ GeV is distinctively affected by confinement of strong interactions (QCD), due to the corresponding sharp decrease in the number of relativistic species. Bayesian analyses in the NANOGrav 15 years and the previous International PTA datasets reveal a significant improvement in the fit with respect to cubic power-law spectra, previously employed for the causality tail. This suggests that the inclusion of Standard Model effects on GWs can have a potentially decisive impact on model selection., 5+11 pages, 7 figures. v2: Analysis with NANOGrav 15 yrs added, minor corresponding changes in abstract and text, references added

We investigate the production of particle Dark Matter (DM) in a minimal freeze-in model considering a non-instantaneous reheating phase after inflation. We demonstrate that for low reheating temperatures, bosonic or fermionic reheating from monomial potentials can lead to a different evolution in the DM production and hence to distinct predictions for the parent particle lifetime and mass, constrained by long-lived particle (LLP) searches. We highlight that such scenario predicts parent particle decay lengths larger compared to using the instantaneous reheating approximation. Moreover, we demonstrate the importance of an accurate definition of the reheating temperature and emphasize its relevance for the correct interpretation of experimental constraints. We explore different models of inflation, which can lead to the considered reheating potential. We find that the extent to which the standard DM freeze-in production can be modified crucially depends on the underlying inflationary model. Based on latest CMB constraints, we derive lower limits on the decay length of the parent particle and confront these results with the corresponding reach of LLP searches. Our findings underscore the impact of the specific dynamics of inflation on DM freeze-in production and highlight their importance for the interpretation of collider signatures. At the same time, our results indicate the potential for LLP searches to shed light on the underlying dynamics of reheating., 14 pages + appendices, 10 figures

We present arguments for including observations with all of the Wide Field Instrument imaging filters, with the exception of F146, within the Nancy Grace Roman Space Telescope (\emph{Roman}) High Latitude Time Domain Survey (HLTDS). Our case is largely driven by the extragalactic deep field science that can be accomplished with HLTDS observations and also by the improvements in type Ia supernova (SN Ia) cosmology systematics that a wide wavelength coverage affords., Submitted in response to the call for community input to Roman core community surveys

We analyze cosmic superstring models in light of NANOGrav 15-year pulsar timing data. A good fit is found for a string tension $G \mu \sim 10^{-12} - 10^{-11}$ and a string intercommutation probability $p \sim 10^{-3} - 10^{-1}$. Extrapolation to higher frequencies assuming standard Big Bang cosmology is compatible at the 68\% CL with the current LIGO/Virgo/KAGRA upper limit on a stochastic gravitational wave background in the 10 to 100 Hz range. The superstring interpretation of the NANOGrav data would be robustly testable by future experiments even in modified cosmological scenarios., Comment: 7 pages 4 figures. Typos fixed and new references added

Supermassive black hole binaries source gravitational waves measured by Pulsar Timing Arrays. The frequency spectrum of this stochastic background is predicted more precisely than its amplitude. We argue that Dark Matter friction can suppress the spectrum around nHz frequencies, where it is measured, allowing to derive robust and significant bounds on the Dark Matter density, which, in turn, controls indirect detection signals from galactic centers. A precise spectrum of gravitational waves would translate in a tomography of the DM density profile, potentially probing DM particle-physics effects that induce a characteristic DM density profile, such as DM annihilations or de Broglie wavelength., 16 pages, 3 figures. v2: factor {\pi} fixed, references added. Webinar presentation: https://www.youtube.com/watch?v=NHGdNLOZ0uc

The Nancy Grace Roman Space Telescope's (RST) Wide Field Imager (WFI) is equipped with a slitless prism that can be used for spectroscopic discovery and follow-up of explosive transients at high redshift as part of its High Latitude Time Domain Survey. This is new and unique spectroscopic capability, not only for its original purpose for cosmology, but also for other types of explosive transients. This white paper is intended to help make this new capability more clear to the community. The depth of the RST prism compared to ground-based spectrographs is explored, showing that the RST prism will be unrivaled in the observer-frame NIR. The influence of the selected sky locations on the speed and homogeneity of a RST prism survey is also estimated. This unique new capability should be considered when balancing the HLTDS time devoted to cadenced imaging and spectroscopy.

We use Bayesian inference and nested sampling to develop a non-parametric method to reconstruct the primordial power spectrum $P_{\mathcal{R}}(k)$ from Large Scale Structure (LSS) data. The performance of the method is studied by applying it to simulations of the clustering of two different object catalogues, low-$z$ (ELGs) and high-$z$ (QSOs), and considering two different photometric errors. These object clusterings are derived from different templates of the primordial power spectrum motivated by models of inflation: the Standard Model power law characterized by the two parameters $A_s$ and $n_s$; a local feature template; and a global oscillatory template. Our reconstruction method involves sampling $N$ knots in the log $\{k,P_{\mathcal{R}}(k)\}$ plane. We use two statistical tests to examine the reconstructions for signs of primordial features: a global test comparing the evidences and a novel local test quantifying the power of the hypothesis test between the power law model and the marginalized probability over $N$ model. The method shows good performance in all scenarios considered. In particular, the tests show no feature detection for the SM. The method is able to detect power spectrum deviations at a level of $\approx 2\%$ for all considered features, combining either the low-$z$ or the high-$z$ redshift bins. Other scenarios with different redshift bins, photometric errors, feature amplitudes and detection levels are also discussed. In addition, we include a first application to real data from the Sloan Digital Sky Survey Luminous Red Galaxy Data Release 4 (SDSS LRG 04), finding no preference for deviations from the primordial power law. The method is flexible, model independent, and suitable for its application to existing and future LSS catalogues., 39 pages, 21 figures, submitted to JCAP

In this white paper, we review five top considerations for selecting locations of the fields of the Roman High-latitude Time Domain Survey. Based on these considerations, we recommend Akari Deep Field South (ADFS)/Euclid Deep Field South (EDFS) in the Southern Hemisphere has it avoids bright stars, has minimal Milky Way dust, is in Roman Continuous viewing zone, overlaps with multiple past and future surveys, and minimal zodiacal background variation. In the North, Extended Groth Strip (EGS) is good except for its zodiacal variation and Supernova/Acceleration Probe North (SNAP-N) and European Large Area Infrared Space Observatory Survey-North 1 (ELAIS N-1) are good except for their synergistic archival data., Submitted to the Roman Core Community Survey call for white papers

Model-independent tests of gravity with cosmology are important when testing extensions to the standard cosmological model. To maximise the impact of these tests one requires predictions for the matter power spectrum on non-linear scales. In this work we validate the \texttt{ReACT} approach to the non-linear matter power spectrum against a suite of phenomenological modified gravity N-body simulations with a time-varying gravitational constant, covering a wider range of parameter space than previously examined. This vanilla application of \texttt{ReACT} has limited range and precision due to the different concentration-mass relation $c(M)$ that occurs when gravity is modified. We extend this approach with a fitting function for a modified concentration-mass relation, allowing for accurate (1$\%$) computation of the matter power spectrum up $k=2\,h\,{\rm Mpc}^{-1}$ across a substantial range of parameter space. This fitting function allows precision model-independent tests of modified gravity to be carried out using the data from upcoming large scale structure surveys., 28 pages, 13 figures Comments Welcome!

Various pulsar timing array (PTA) experiments (NANOGrav, EPTA, PPTA, CPTA, including data from InPTA) very recently reported evidence for excess red common-spectrum signals in their latest datasets, with inter-pulsar correlations following the Hellings-Downs pattern, pointing to a stochastic gravitational wave background (SGWB) origin. Focusing for concreteness on the NANOGrav signal (given that all signals are in good agreement between each other), I inspect whether it supports an inflationary SGWB explanation, finding that such an interpretation calls for an extremely blue tensor spectrum, with spectral index $n_T \simeq 1.8 \pm 0.3$, while Big Bang Nucleosynthesis limits require a very low reheating scale, $T_{\rm rh} \lesssim 10\,{\rm GeV}$. While not impossible, an inflationary origin for the PTA signal is barely tenable: within well-motivated inflationary models it is hard to achieve such a blue tilt, whereas models who do tend to predict sizeable non-Gaussianities, excluded by observations. Intriguingly, ekpyrotic models naturally predict a SGWB with spectral index $n_T=2$, although with an amplitude too suppressed to be able to explain the signal detected by PTA experiments. Finally, I provide explicit expressions for a bivariate Gaussian approximation to the joint posterior distribution for the intrinsic-noise amplitude and spectral index of the NANOGrav signal, which can facilitate extending similar analyses to different theoretical signals., 16 pages, 3 figures, centered around NANOGrav. v2: additional references (especially on other interpretations of the recent PTA signals) added, version accepted for publication in JHEAp

The current reference High-latitude time domain survey increases the completeness of transients with prism temporal time series data by adjusting the ratio of prism-to-imaging time. However, there are two other nobs that allow for a more complete prism coverage: prism cadence and exposure time. In this white paper, we discuss how changes to the prism cadence and exposure time -- in order to increase the fraction of observed transients with spectral time series -- affect supernova cosmology, transient typing and template building, and the study of rare transients., Submitted to the Roman Core Community Survey call for white papers

Very recently, the Pulsar Timing Array (PTA) experiments reported strong evidence for the presence of the nanohertz stochastic gravitational wave background (SGWB). In this work we show that the cosmic string loops can account for the nanohertz SGWB data with a $G\mu \sim 2\times 10^{-12}$ and the loops number density $N \sim 10^{4}$. Though the presence of cosmic string loops can also effectively enhance the number density of massive galaxies at high redshifts, we do not find a reasonable parameter space to self-consistently interpret both the SGWB data and the JWST observations. This implies either an extension of the model adopted in this work or the different physical origins of these two phenomena.

Several pulsar timing array collaborations recently reported evidence of a stochastic gravitational wave background (SGWB) at nHz frequencies. Whilst the SGWB could originate from the merger of supermassive black holes, it could be a signature of new physics near the 100 MeV scale. Supercooled first-order phase transitions that end at the 100 MeV scale are intriguing explanations, because they could connect the nHz signal to new physics at the electroweak scale or beyond. Here, however, we provide a clear demonstration that it is not simple to create a nHz signal from a supercooled phase transition, due to two crucial issues that should be checked in any proposed supercooled explanations. As an example, we use a model based on non-linearly realized electroweak symmetry that has been cited as evidence for a supercooled explanation. First, we show that a FOPT cannot complete for the required transition temperature of around 100 MeV. Such supercooling implies a period of vacuum domination that hinders bubble percolation and transition completion. Second, we show that even if completion is not required or if this constraint is evaded, the Universe typically reheats to the scale of any physics driving the FOPT. This redshifts the SGWB away from the required nHz range., 10 pages, 4 figures

We argue that field trajectories, which lead to cosmic acceleration and feature rapid turns near the boundary of the moduli space, are in the Swampland. We obtain this result by assuming the validity of the Swampland Distance Conjecture (SDC) in the presence of a positive scalar potential and by focusing on hyperbolic spaces, as prototype geometries of infinite distance limits of Calabi-Yau compactifications. We find that, in a quasi-de Sitter space with Hubble rate $H$ and acceleration parameter $\epsilon$, the turning rate $\Omega$ is upper bounded such as $\Omega/H, Comment: 34 pages, 1 figure, 2 appendices

The pattern of neutrino flavor oscillations could be altered by the influence of noisy perturbations such as those arising from a gravitational wave background (GWB). A stochastic process that is consistent with a GWB has been recently reported by the independent analyses of pulsar timing array (PTA) data sets collected over a decadal timescale by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), the European Pulsar Timing Array (EPTA), the Parkes Pulsar Timing Array (PPTA), and the Chinese Pulsar Timing Array (CPTA) collaborations. We investigate the modifications in the neutrino flavor oscillations under the influence of the GWB reported by the PTA collaborations and we discuss how such effects could be potentially revealed in near-future neutrino detectors, possibly helping the discrimination of different models for the GWB below the nHz frequency range., 5 pages, 2 figures

The non-linear relationship between the monochromatic X-ray and UV luminosities in quasars offers the possibility of using high-z quasars as standard candles for cosmological testing. In this paper, we use a high-quality catalog of 1598 quasars extending to redshift 6, to compare the flat and uniformly expanding cosmological model, $R_h$ = ct and $\Lambda$CDM cosmological models which are the most debated. The quasar samples are mainly from the XMM-Newton and the Sloan Digital Sky Survey (SDSS). The final result is that the Akaike Information Criterion favors $\Lambda$CDM over $R_h$=ct with a relative probability of 86.30% versus 13.70%., Comment: 10 pages, 5 figures, Accepted for publication in APSS