arXiv subjects

Marzieh Farhang

Publications and source records attributed to Marzieh Farhang.

At least 19 recordsLinked to original sources

arXiv2026

CMB Bounds on Primordial Black Holes via Radiation Capture

We explore the capture of neutrinos and photons in the cosmic neutrino and photon background by primordial black holes (PBHs). We model this phenomenon as a gravitational interaction that effectively modifies the continuity equations for radiation and PBH densities and the cosmic expansion history. We find that the observability of this modified cosmic history is highly sensitive to PBH mass, and only extraordinarily massive PBHs would leave observable trace on the temperature and E-mode polarization of the cosmic microwave background (CMB). Specifically, Planck data restrict PBH abundance to $f_{\rm pbh}\lesssim 10^{-1}$ for PBH masses above $10^{15} M_\odot$, getting considerably tighter for higher masses. We expect substantial improvement as high-resolution measurements of larger CMB multipoles become available. A future cosmic-variance-limited experiment, with $\ell_{\rm max}=7000$, would set $f_{\rm pbh}\lesssim 10^{-1}-8\times 10^{-5}$ (for the fiducial $Λ$CDM cosmology) across $10^{13}-10^{18}M_\odot$. These constraints would be comparable to the current limits at the high-mass end of the spectrum [Carr et al, 2026]. The gravitational interaction of PBHS with the cosmic background radiation and its imprints on CMB would thus provide an independent complementary probe of extraordinarily massive PBH abundance.

astro-ph.CO↗

arXiv2024

A Semiblind Reconstruction of the History of Effective Number of Neutrinos Using CMB Data

We explore the possibility of redshift-dependent deviations in the contribution of relativistic degrees of freedom to the radiation budget of the cosmos, conventionally parameterized by the effective number of neutrinos $N_{\rm eff}$, from the predictions of the standard model. We expand the deviations $ΔN_{\rm eff}(z)$ in terms of top-hat functions and treat their amplitudes as the free parameters of the theory to be measured alongside the standard cosmological parameters by the Planck measurements of the cosmic microwave background (CMB) anisotropies and Baryonic Acoustic Oscillations, as well as performing forecasts for futuristic CMB surveys such as PICO and CMB-S4. We reconstruct the history of $ΔN_{\rm eff}$ and find that with the current data the history is consistent with the standard scenario. Inclusion of the new degrees of freedom in the analysis increases $H_0$ to $68.71\pm 0.44$, slightly reducing the Hubble tension. With the smaller forecasted errors on the $ΔN_{\rm eff}(z)$ parametrization modes from future CMB surveys, very accurate bounds are expected within the possible range of dark radiation models.

astro-ph.CO↗

arXiv2024

Compact Binary Merger Rate with Modified Gravity in Dark-Matter Spikes

In this study, we investigate the impact of modified gravity on the merger rate of compact binaries within dark-matter spikes surrounding super-massive black holes (SMBHs). Specifically, we calculate binary merger rates involving primordial black holes (PBHs) and/or neutron stars (NSs) in Hu-Sawicki $f(R)$ gravity and the normal branch of Dvali-Gabadadze-Porrati (nDGP) gravity, with three SMBH mass functions, Benson, Vika, and Shankar. The results show consistently higher merger rates predicted for PBH-PBH and PBH-NS binaries in these gravity models compared to general relativity (GR), in particular at lower SMBH masses and for steeper dark-matter spike density profiles. The predicted merger rates are compared to the LIGO-Virgo observations to constrain the parameters of the theory. In particular we find steeper dark-matter spike density profiles in the modified gravity scenarios compared to GR. When compared to current observational constraints on PBH abundance, the mass ranges allowed by Hu-Sawicki $f(R)$ models are found to be wider than by nDGP models, for given merger rates. The results are highly dependent on the choice of SMBH mass function, with Vika and Shankar mass functions predicting lower abundances. The considerable sensitivity of the results on the assumed gravity scenario and SMBH mass function demonstrates the necessity of incorporating the corresponding theoretical uncertainties in making relatively robust predictions on compact binary merger rates and, as a result on PBH properties.

gr-qc↗

arXiv2024

Sensitivity of Cosmological Parameter Estimation to Nonlinear Prescription from Cosmic Shear

Several ongoing and upcoming large scale structure surveys aim to explore the nonlinear regime of structure formation with high precision. Making reliable cosmological inferences from these observations necessitates precise theoretical modeling of the mildly nonlinear regime. In this work we explore how the choice of nonlinear prescription would impact parameter estimation from cosmic shear measurements for a Euclid-like survey. Specifically, we employ two different nonlinear prescriptions of Haloft and the Effective Field Theory of the Large Scale Structure and compare their measurements for the three different cosmological scenarios of $Λ$CDM, $w$CDM and $(w_0,w_a)$CDM. We also investigate the impact of different nonlinear cutoff schemes on parameter estimation. We find that the predicted errors on most parameters shrink considerably as smaller scales are included in the analysis, with the amount depending on the nonlinear prescription and the cutoff scheme used. We use predictions from the Halofit model to analyze the mock data from DarkSky $N$-body simulations and quantify the parameter bias introduced in the measurements due to the choice of nonlinear prescription. We observe that $σ_8$ and $n_{\rm{s}}$ have the largest measurement bias induced by inaccuracies of the Halofit model.

astro-ph.CO↗

arXiv2024

Toward More Realistic Mass Functions For Ultradense Dark Matter Halos

Ultradense dark matter halos (UDMHs) are high concentrations of dark matter, assumed to have formed deep in the radiation-dominated era from amplified primordial perturbations. In this work we improve the previous works for the calculation of UDMH abundance by elaborating on the formation process of these halos by including various physical and geometrical modifications in the analysis. In particular, we investigate the impact of angular momentum, dynamical friction and triaxial collapse on the predicted mass functions for UDMHs. We perform the calculations for four primordial power spectra with different amplified features that allow for primordial black hole and UDHM formation in wide and narrow mass ranges. We also apply this analysis in the context of two possible scenarios for dark matter: the single-component and the multi-component. We find that the abundance of UDMHs is prominently enhanced in the presence of these more realistic mass functions.

astro-ph.CO↗

arXiv2024

Primordial Black Hole-Neutron Star Merger Rate in Modified Gravity

In this work we investigate the merger rate of primordial black hole-neutron star (PBH-NS) binaries in two widely-studied modified gravity (MG) models: Hu-Sawicki $f(R)$ gravity and the normal branch of Dvali-Gabadadze-Porrati (nDGP) gravity. In our analysis, we take into account the effects of MG on the halo properties including halo mass function, halo concentration parameter, halo density profile, and velocity dispersion of dark matter particles. We find that these MG models, due to their stronger gravitational field induced by an effective fifth force, predict enhanced merger rates compared to general relativity. This enhancement is found to be redshift-dependent and sensitive to model parameters, PBH mass and fraction. Assuming PBH mass range of $5-50 M_{\odot}$, we compare the predicted merger rate of PBH-NS binaries with those inferred from LIGO-Virgo-KAGRA observations of gravitational waves (GWs). We find that the merger rates obtained from MG models will be consistent with the GW observations, if the abundance of PBHs is relatively large, with the exact amount depending on the MG model and its parameter values, as well as PBH mass. We also establish upper limits on the abundance of PBHs in these MG frameworks while comparing with the existing non-GW constraints, which can potentially impose even more stringent constraints.

gr-qc↗

arXiv2023

Reconstruction of A Scale-Dependent Gravitational Phase Transition

In this work we extend our earlier phenomenological model for a gravitational phase transition (GPT) and its generalization to early times by letting the modifications in the linearly-perturbed Einstein equations be scale-dependent. These modifications are characterized as deviations of the parameters $μ(z,k)$ and $γ(z,k)$ from their values in general relativity (GR). The scale-dependent amplitudes of modified $μ(z,k)$ and $γ(z,k)$ and the parameters defining the phase transition, along with the standard cosmological parameters, are measured by various data combinations. Out of the perturbation parameters, we construct gravity eigenmodes which represent patterns of perturbations best detectable by data. We detect no significant deviation from GR in these parameters. However, the larger parameter space produced due to the new degrees of freedom allows for the reconciliation of various datasets which are in tension in $Λ$CDM. In particular, we find $H_0=71.9\pm 9.2$ from anisotropies of the Cosmic Microwave Background as measured by Planck and various measurements of the Baryonic Acoustic Oscillations, in agreement with local Hubble measurements. We also find that the $σ_8$ tension between the measurements of Dark Energy Survey and Planck is reduced to less than $1σ$.

astro-ph.CO↗

arXiv2021

Consistency of Planck Data With Power-Law Primordial Scalar Power Spectrum

In this work we explore the possibility of variations in the primordial scalar power spectrum around the power-law shape, as predicted by single-field slow-roll inflationary scenarios. We search for the trace of these fluctuations in a semi-blind, model-independent way on the observations of the Cosmic Microwave Background (CMB) sky. In particular we use two sets of perturbation patterns, specific patterns with typical features such as oscillations, bumps and transitions, as well as perturbation modes, constructed from the eigenanalysis of the forecasted or measured covariance of perturbation parameters. These modes, in principle, span the parameter space of all possible perturbations to the primordial spectrum, and when rank-ordered, the ones with the highest detectability would suffice to explore the constrainable features around the power-law spectrum in a data-driven (and not theoretically-biased) manner. With Planck measurements of CMB anisotropies, the amplitudes of all perturbation patterns considered in this work are found to be consistent with zero. This finding confirms, in the absence of theoretical biases, the consistency of the Planck data with the assumption of power-law inflationary pattern for the primordial spectrum.

astro-ph.CO↗

arXiv2021

Phenomenological Gravitational Phase Transition: Early and Late Modifications

In this work we generalize the idea of a gravitational phase transition or GPT at late times to allow for a modified gravity scenario in the early universe as well. The original GPT was shown to simultaneously relax the $H_0$ and $σ_8$ tensions and {\it Planck} internal inconsistencies. However, the primary results from GPT predictions implied disagreement with the data from the baryonic acoustic oscillations (BAO). Here we investigate whether the generalized GPT scenario could address the Hubble tension in the presence of the BAO data as well. We find that, despite the vastly enlarged gravitational parameter space, the BAO data strongly prefer the $Λ$CDM paradigm with a low inferred Hubble constant, $68.03\pm 0.76 $ km/s/Mpc, in tension with the local $H_0$ measurements from Riess et al., $H_0=74.03\pm 1.42$ km/s/Mpc. This failure of the generalized GPT scenario to host the P18-BAO-R19 trio is of significance and noticeably shrinks the space of possible gravitational solutions to the Hubble tension.

astro-ph.CO↗

arXiv2021

Sensitivity of Cosmological Parameter Estimation to Nonlinear Prescription from Galaxy Clustering

Next generation large scale surveys probe the nonlinear regime with high resolution. Making viable cosmological inferences based on these observations requires accurate theoretical modeling of the mildly nonlinear regime. In this work we investigate the sensitivity of cosmological parameter measurements from future probes of galaxy clustering to the choice of nonlinear prescription up to $k_{\rm max}=0.3~h~\rm{Mpc}^{-1}$. In particular, we calculate the induced parameter bias when the mildly nonlinear regime is modeled by the Halofit fitting scheme. We find significant ($\sim5σ$) bias for some parameters with a future Euclid-like survey. We also explore the contribution of different scales to the parameter estimation for different observational setups and cosmological scenarios, compared for the two nonlinear prescriptions of Halofit and EFTofLSS. We include in the analysis the free parameters of the nonlinear theory and a blind parametrization for the galaxy bias. We find that marginalization over these nuisance parameters significantly boosts the errors of the standard cosmological parameters. This renders the differences in the predictions of the various nonlinear prescriptions less effective when transferred to the parameter space. More accurate modeling of these nuisance parameters would therefore greatly enhance the cosmological gain from the mildly nonlinear regime.

astro-ph.CO↗

arXiv2021

Detectable Data-driven Features in the Primordial Scalar Power Spectrum

In this work we explore the power of future large-scale surveys to constrain possible deviations from the standard single-field slow-roll inflationary scenario. Specifically, we parametrize possible fluctuations around the almost scale-invariant primordial scalar power spectrum in a model independent way. We then use their imprints on the simulated matter distribution, as observed by the galaxy clustering and weak lensing probes of Euclid and Square Kilometer Array, to construct the best constrainable patterns of fluctuations. For comparison, we make similar forecasts for a futuristic CMB-S4-like survey. The modes are found to have similar, yet shifted, patterns, with increasing number of wiggles as the mode number increases. The forecasted constraints are tightest for CMB anisotropies and galaxy clustering, depending on the details of the specifications of the survey. As case studies, we explore how two greatly different physically motivated patterns of primordial power spectrum are reconstructed by the proposed modes. We propose a figure of merit based on the amount of information delivered by the modes to truncate the mode hierarchy which is automatically generated by the analysis.

astro-ph.CO↗

arXiv2021

CMB Cold Spot in the Planck light

The Cold Spot, with an unusually cold region surrounded by a hot ring, is a statistically significant anomaly in the Cosmic Microwave Background (CMB) sky. In this work we assess whether different sets of multiple subvoids based on the 2dF-VST ATLAS Cold Spot galaxy redshift survey or a collapsing cosmic texture could have produced such an anomaly through a simultaneous search for their gravitational redshift and lensing signatures on the {\it Planck} CMB temperature anisotropies. We use patches with radii $R=10^\circ$ and $R=20^\circ$ to account for the inner cold region as well as the outer hot ring. As the void model, we explore two sets of $Λ$LTB templates characterized by different values of the model's free parameters, and a top-hat void template. We detect higher-than-expected gravitational redshift amplitudes for the first two sets, $\mathcal{A}_{\rm rs}=5.4\pm 1.4$ and $\mathcal{A}_{\rm rs}=14.4\pm 3.8$, and lower than expected for the top-hat model, $\mathcal{A}_{\rm rs}=0.3 \pm 0.1$. The amplitudes for the lensing imprint are consistent with zero for all these subvoid models. The estimated amplitude for the texture imprint from the gravitational redshift measurement implies the energy scale of the texture, parametrized by $ε$, to be $ε= (7.6\pm2.0)\times 10^{-5}$, with no detection of the lensing trace. We note that the deviation of the subvoid amplitudes from unity and the inability of the texture and some of the void profiles to reproduce the hot ring indicate theoretical insufficiencies, either in the construction of the model or in the assumed gravitational and cosmological framework leading to the imprints for the structures.

astro-ph.CO↗

arXiv2020

Phenomenological Gravitational Phase Transition: Reconciliation between the Late and Early Universe

In this work we investigate whether a certain phenomenological extension to the general relativity (GR), in the form of a gravitational phase transition (GPT) in the Universe, can reduce the external $Planck$ tensions with the local Hubble measurements and the distribution of matter, characterized by $σ_8$, as well as its internal inconsistencies in the lensing amplitude and the low--high $\ell$ parameter estimates. We introduce new degrees of freedom into the background and the two scalar perturbation equations in the Newtonian gauge, with simultaneous transitions from an early gravitational phase equivalent to GR toward a late phase. We model the transition as a "tanh" parametrized by the transition redshift $z_{\rm t}$ and width $α$, with amplitudes $Λ(z)$ and $(μ(z),γ(z))$ for the background and perturbations respectively. We verify the consistency of the datasets used in this work in the GPT framework and confirm that the individual tensions do not require conflicting transitions. We find that the joint datasets prefer a recent transition at $z_{\rm t}\approx 0.9$ in the background and perturbed Einstein equations, driven mainly by the local Hubble measurement. This transition relaxes all the tensions considered in this work.

astro-ph.CO↗

arXiv2014

Pointing control for the SPIDER balloon-borne telescope

We present the technology and control methods developed for the pointing system of the SPIDER experiment. SPIDER is a balloon-borne polarimeter designed to detect the imprint of primordial gravitational waves in the polarization of the Cosmic Microwave Background radiation. We describe the two main components of the telescope's azimuth drive: the reaction wheel and the motorized pivot. A 13 kHz PI control loop runs on a digital signal processor, with feedback from fibre optic rate gyroscopes. This system can control azimuthal speed with < 0.02 deg/s RMS error. To control elevation, SPIDER uses stepper-motor-driven linear actuators to rotate the cryostat, which houses the optical instruments, relative to the outer frame. With the velocity in each axis controlled in this way, higher-level control loops on the onboard flight computers can implement the pointing and scanning observation modes required for the experiment. We have accomplished the non-trivial task of scanning a 5000 lb payload sinusoidally in azimuth at a peak acceleration of 0.8 deg/s$^2$, and a peak speed of 6 deg/s. We can do so while reliably achieving sub-arcminute pointing control accuracy.

astro-ph.IM↗

arXiv2013

Cosmological Parameters from Pre-Planck CMB Measurements

Recent data from the WMAP, ACT and SPT experiments provide precise measurements of the cosmic microwave background temperature power spectrum over a wide range of angular scales. The combination of these observations is well fit by the standard, spatially flat LCDM cosmological model, constraining six free parameters to within a few percent. The scalar spectral index, n_s = 0.9690 +/- 0.0089, is less than unity at the 3.6 sigma level, consistent with simple models of inflation. The damping tail of the power spectrum at high resolution, combined with the amplitude of gravitational lensing measured by ACT and SPT, constrains the effective number of relativistic species to be N_eff = 3.28 +/- 0.40, in agreement with the standard model's three species of light neutrinos.

astro-ph.CO↗

arXiv2011

Semi-blind Eigen-analyses of Recombination Histories Using CMB Data

Cosmological parameter measurements from CMB experiments such as Planck, ACTpol, SPTpol and other high resolution follow-ons fundamentally rely on the accuracy of the assumed recombination model, or one with well prescribed uncertainties. Deviations from the standard recombination history might suggest new particle physics or modified atomic physics. Here we treat possible perturbative fluctuations in the free electron fraction, $\Xe(z)$, by a semi-blind expansion in densely-packed modes in redshift. From these we construct parameter eigenmodes, which we rank order so that the lowest modes provide the most power to probe the $\Xe(z)$ with CMB measurements. Since the eigenmodes are effectively weighed by the fiducial $\Xe$ history, they are localized around the differential visibility peak, allowing for an excellent probe of hydrogen recombination, but a weaker probe of the higher redshift helium recombination and the lower redshift highly neutral freeze-out tail. We use an information-based criterion to truncate the mode hierarchy, and show that with even a few modes the method goes a long way towards morphing a fiducial older {\sc Recfast} $X_{\rm e,i} (z)$ into the new and improved {\sc CosmoRec} and {\sc HyRec} $X_{\rm e,f} (z)$ in the hydrogen recombination regime, though not well in the helium regime. Without such a correction, the derived cosmic parameters are biased. We discuss an iterative approach for updating the eigenmodes to further hone in on $X_{\rm e,f} (z)$ if large deviations are indeed found. We also introduce control parameters that downweight the attention on the visibility peak structure, e.g., focusing the eigenmode probes more strongly on the $\Xe (z)$ freeze-out tail, as would be appropriate when looking for the $\Xe$ signature of annihilating or decaying elementary particles.

astro-ph.CO↗

arXiv2011

Primordial Gravitational Wave Detectability with Deep Small-Sky CMB Experiments

We use Bayesian estimation on direct T-Q-U CMB polarization maps to forecast errors on the tensor-to- scalar power ratio r, and hence on primordial gravitational waves, as a function of sky coverage fsky. This method filters the quadratic pixel-pixel space into the optimal combinations needed for r detection for cut skies, providing enhanced information over a first-step linear separation into a combination of E, B and mixed modes, and ignoring the latter. With current computational power and for typical resolutions appropriate for r detection, the large matrix inversions required are accurate and fast. We explore two classes of experiments. One is motivated by a long duration balloon experiment like Spider, with pixel noise \propto \sqrt{fsky} for a specified observing period, but also applies to ground-based array experiments. We find that, ignoring systematic effects and foregrounds, an experiment with Spider-like noise over fsky ~0.02-0.2 could place a 2sigma_r ~0.014 (~95% CL) bound, rising to 0.02 with an L-dependent foreground residual. We contrast this with a Planck-like fixed instrumental noise as fsky varies, which gives a Galaxy-masked (fsky = 0.75) 2sigma_r ~0.015, rising to ~0.05 with the foreground residuals. Using for a figure of merit the (marginalized) 1D Shannon entropy of r, taken relative to the first 2003 WMAP1 CMB-only constraint, gives -1.7 (-1.9) bits from the 2010 WMAP7+ACT (2011 WMAP7+SPT) data, forecasts of -6 bits from Spider (plus Planck), of up to -11 bits for post-Planck satellites and -13 bits for a perfect cosmic variance limited experiment. We thus confirm the wisdom of the current strategy for r detection of deeply probed patches covering the fsky minimum-error trough with balloon and ground experiments.

astro-ph.CO↗

arXiv2010

Modeling and characterization of the SPIDER half-wave plate

Spider is a balloon-borne array of six telescopes that will observe the Cosmic Microwave Background. The 2624 antenna-coupled bolometers in the instrument will make a polarization map of the CMB with approximately one-half degree resolution at 145 GHz. Polarization modulation is achieved via a cryogenic sapphire half-wave plate (HWP) skyward of the primary optic. We have measured millimeter-wave transmission spectra of the sapphire at room and cryogenic temperatures. The spectra are consistent with our physical optics model, and the data gives excellent measurements of the indices of A-cut sapphire. We have also taken preliminary spectra of the integrated HWP, optical system, and detectors in the prototype Spider receiver. We calculate the variation in response of the HWP between observing the CMB and foreground spectra, and estimate that it should not limit the Spider constraints on inflation.

astro-ph.IM↗