CyberSec Research

Sub-solar mass black holes could show up in gravitational observations in future and near-solar mass black holes might have been involved in the events GW190425 and GW190814. Since they cannot form from the stellar evolution, their creation requires exotic mechanisms. One such mechanism involves the capture of dark matter particles by stellar objects and their thermalization. When the criterion for the collapse of these dark matter particles is satisfied, a tiny endoparasitic black hole (EBH) forms and then it accretes matter from the host. The EBH may transmute the host into a black hole of nearly the same mass as the host or lesser, depending on the type of accretion. We examine this complex and poorly explored accretion mechanism, considering the effects of rotation and viscosity but ignoring some other effects, such as those of pressure and magnetic field, as the first step. Using a general framework to assess the effects of rotation and viscosity on accretion, we show that the accretion could be stalled in some white dwarfs, but not in neutron stars. The stalled accretion should cause an opening in the host's polar regions, the extent of which depends on the mass and spin of the host.

Under $\Lambda$CDM, recent baryon acoustic oscillation (BAO) distance measures from DESI, which favor a low matter density $\Omega_m$, are in moderate $2-3\sigma$ tension with cosmic microwave background (CMB) observations. This tension appears alternately as a preference for the sum of neutrino masses dropping below the $\sum m_\nu = 0.06$eV value required by neutrino oscillation measurements to formally negative values; a discrepant value of $\Omega_m$ at 0.06eV; or preference for dynamical dark energy beyond $\Lambda$CDM. We show that this tension largely arises from the CMB lensing constraints on the calibration of the sound horizon for geometric measurements and relies on the measurement of the reionization optical depth $\tau$ from large-angle CMB polarization to set the lensing amplitude. Dropping these constraints removes the neutrino tension at $\sum m_\nu=0.06$eV entirely, favoring $\tau = 0.091\pm 0.011$ in $\Lambda$CDM. Beyond $\Lambda$CDM, it brings the preference for $w_0-w_a$ dynamical dark energy to below $95\%$ CL. We explore the freedom in interpreting the low-$\ell$ EE polarization constraint due to analysis choices and reionization modeling beyond the standard step-function assumption and find that this drops the neutrino tension in $\Lambda$CDM to below $95\%$ CL. Alternately, this raising of $\tau$ can also be achieved by the same reduction in large-scale curvature fluctuations that also ameliorates the low-$\ell$ temperature anomaly.

NGC 1068 is the brightest extragalactic source in high-energy neutrinos as seen by IceCube, yet the accompanying gamma-ray flux is orders of magnitude weaker. It has been argued that this indicates that the bulk of neutrinos and gamma rays are emitted in the innermost vicinity of the central supermassive black hole, which is transparent to neutrinos, but opaque to gamma rays. Even in such extreme scenarios for the acceleration of cosmic rays, astrophysical models typically overestimate the low-energy gamma-ray flux and/or require some fine-tuning in the physical parameters. Here we suggest instead that the dark matter surrounding the supermassive black hole may absorb the gamma rays, inducing the observed deficit. We show that for a dark matter-photon scattering cross section in the range $\sigma_{\rm DM-\gamma}/m_{\rm DM} \simeq 10^{-28}-10^{-30}$ cm$^2$/GeV, Fermi-LAT measurements can be well reconciled with IceCube data. We also present some simple particle physics examples that achieve the correct spectral energy dependence while respecting complementary constraints.

We investigate the potential of $\beta$-cosmic-web weighted angular correlation functions to improve the cosmological constraints. Using SDSS DR12 CMASS-NGC galaxies and simulated mock catalogs with $\Omega_m$ varying in the range of 0.25-0.40, we quantify the discriminative power of different statistics via $\Delta \chi^2$ measurements. Our results demonstrate significant improvements when incorporating weighted statistics. Especially, adding the $\bar{D}_{\rm nei}$-weighting statistics enhances $\Delta \chi^2$ by 39%-130%, while adding the $1/\bar{D}_{\rm nei}$-weighted statistics yields 229%-336% gains over solely using the traditional angular statistics. These findings align with 3D correlation function studies \cite{Yin+etal+2024}, confirming the superior performance of $\beta$-cosmic-web weighted statistics. The thin-redshift-slice approach makes our method particularly relevant for slitless surveys (such as Euclid, CSST) where redshift errors challenge traditional 3D analyses. This work also establishes the first theoretical framework for marked statistics in 2D angular clustering.

The nature of dark matter is one of the most fundamental questions in cosmology. Using the cosmic microwave background (CMB), type Ia supernova (SN) and DESI's new measurements of baryon acoustic oscillations (BAO), we find the robust $\sim2\,\sigma$ evidences of the evolution of dark matter in the dynamical dark matter (DDM) model, $\omega_{dm}(a)=\omega_{dm0}+\omega_{dma}(1-a)$. Based on CMB data, we find a very strong linear relation $\omega_{dma}=-\omega_{dm0}$, inducing the single-parameter DDM model, $\omega_{dm}(a)=\omega_{dm}a$, where the $\sim2\,\sigma$ DDM evidences is well captured and even strengthened. We demonstrate that there are beyond $2\,\sigma$ evidences of the coexistence of DDM and dynamical dark energy using the combinations of CMB, DESI BAO and Pantheon+ SN data. In such models, at a beyond $5\,\sigma$ confidence level, we verify that the universe remains in a matter-dominated state for a substantial period in the past, accelerate in the distant future and finally becomes completely dominated by dark matter. We propose that the ultimate fate of the universe is the ``Super Rip'' induced by dark matter with an extremely negative pressure. Our findings fundamentally challenge the prevailing understanding of cosmic acceleration and deepen our insight into the universe's evolution.

Primordial power spectra with low power at long wavelengths can alleviate lensing anomaly. However the extent to which data favours such a primordial spectra is not clear. In this work, we investigate power suppression and related mitigation of lensing anomaly with the help of phenomenological models which are valid over scales of interest. We consider simple extensions to nearly scale invariant power spectra such as those which includes running and running of running of spectral index. We perform Bayesian analysis of these models, which are agnostic about power suppression, with various data sets and show that data tend to choose parameters which leads to power suppression at low multipoles. We then analyse the significance of these findings using information criteria. Further, we investigate the ability of near-ultimate future CMB missions such as ECHO to put tighter constraints on these models. We conclude that we can make stronger conclusions about the presence of power suppression in the future by studying such simple phenomenological models.

The cosmological tensions between early- and late-Universe probes, particularly the Hubble tension ($H_0$) and $S_8$ discrepancy, challenge the validity of the standard ${\rm{\Lambda}CDM}$ model. Motivated by these tensions, we perform a comprehensive joint analysis of three representative dark energy models - ${\rm{\Lambda}CDM}$, the Chevallier-Polarski-Linder (CPL) parametrization, and the Phenomenologically Emergent Dark Energy (PEDE) model - using the latest observational datasets: baryon acoustic oscillation (BAO) measurements from DESI Data Releases 1 and 2 (DR1/DR2), the Pantheon Plus sample of Type Ia supernovae (SNe Ia), and time-delay cosmography from TDCOSMO lensing. Our multi-probe approach breaks key degeneracies among cosmological parameters ($H_0$, $r_d$, and $M_B$) and provides robust constraints on dark energy dynamics. The CPL model yields a statistically significant improvement over ${\rm{\Lambda}CDM}$, with $\Delta \chi^2 \approx -3.6$ for DESI DR2+Pantheon Plus+TDCOSMO, favoring a quintessence-like behavior ($w_0=-0.87^{+0.045 }_{-0.045} $, $w_a=-0.41^{+ 0.28}_{-0.28}$ at 1$\sigma$ confidence level). In contrast, the PEDE model exhibits severe tension with observations, yielding $\Delta \chi^2 \approx +53.1$ (DR1) and $\Delta \chi^2 \approx +132.3$ (DR2), despite its potential to marginally alleviate the $H_0$ tension. DESI DR2 tightens constraints on dynamical dark energy by $\sim$40\%, reinforcing evidence for redshift-evolving $w(z)$. Remarkably, our results demonstrate that such data combination can achieve precision comparable to Planck CMB measurements for dynamical dark energy studies, while offering complementary advantages in probing the late-time universe. This synergy between different observational data significantly enhances our ability to constrain dark energy properties.

Observations of microlensed gravitational waves (GWs) emanated by compact binary coalescences (CBCs) are essential for studying the mass density distribution in the universe, including black holes and dark matter halos. However, no confident detection of microlensed GWs have been reported to date. There are two important challenges in the identification of microlensed GWs. The first is that the source waveform and lens structure models are not known a-priori. The second is that certain classes of unlensed GWs could mimic microlensed GWs, resulting in undesirable false alarms. In this work, we propose to use the Kramers-Kronig relation for gravitational lensing systems. We argue that such systems are essentially linear response systems obeying causality, where KK relation must hold. The power of this method lies in the fact that microlensed GWs, regardless of the lens structure, must obey KK relation, while unlensed GW events are not in general expected to obey it. This, in principle, allows us to identify microlensed GWs while dismissing microlensing mimickers. We provide the first important steps towards a methodology that exploits KK relation, and test its usefulness under idealized conditions.

The dynamics of the electroweak phase transition in the early universe has profound implications for cosmology and particle physics. We systematically study the steady-state dynamics of bubble walls in scenarios where the transition is first order within three representative beyond the Standard Model frameworks, characterised by the presence of an additional scalar in different electroweak representations. Focusing on the local thermal equilibrium regime, we numerically solve the coupled scalar and hydrodynamic equations to extract key properties of the phase transition front: the wall velocity, width, plasma and field profiles. Remarkably, we find a near-universal behaviour across models when expressed in terms of thermodynamic quantities, that can be captured by simple fitting functions, useful for phenomenological applications. These results also provide an upper bound on the bubble velocity and represent the first necessary step for the full inclusion of out-of-equilibrium effects.

Analyses of the galaxy N-Point Correlation Functions (NPCFs) have a large number of degrees of freedom, meaning one cannot directly estimate an invertible covariance matrix purely from mock catalogs, as has been the standard approach for the 2PCF and power spectrum. Instead, analyses use templates based on assuming a Gaussian Random Field density with the true, Boltzmann-solver-computed power spectrum. The resulting covariance matrices are sparse but have notable internal structure. To understand this structure better, we seek a fully analytic, closed-form covariance matrix template, using a power law power spectrum $P(k) \propto 1/k$. We obtain a simple closed-form solution for the covariance of the 2PCF, as well as closed-form solutions for the fundamental building blocks of the covariance matrices for the 3PCF, 4PCF, and beyond. We use our results to present a clearer picture of the covariance matrices' structure and sparsity, corresponding to triangular and non-triangular regions. This will be useful in guiding future NPCF analyses with spectroscopic surveys such as DESI, Euclid, Roman, and SPHEREx.

Electromagnetic emissions from astrophysical sources at cosmological distances can be used to estimate the photon mass, $m_{\gamma}$. In this paper, we combine measurements of the dispersion measure ($\mathrm{DM}$) of fast radio bursts (FRB) with the luminosity distance from type Ia supernovae (SNe) to investigate update constraints on the photon rest mass. We derive the expression of $\mathrm{DM}$ dependence concerning a non-vanishing photon mass from a cosmological-model independent approach and constrain the parameter $m_{\gamma}$ from measurements of 68 well-localized FRBs and 1048 SNe data from the Pantheon compilation. We consider two scenarios for the baryon fraction in the intergalactic medium ($f_{\mathrm{IGM}}$): one where the value is fixed according to recent reports and another where it is treated as a free parameter, $f_{\mathrm{IGM}} = f_{\mathrm{IGM,0}}$. In the latter case, we find $m_{\gamma} = (29.4_{-15.5}^{+5.80}) \times 10^{-51}$ kg, at $1\sigma$ level. Our results also demonstrate an anticorrelation between $f_{\mathrm{IGM}}$ and $m_{\gamma}$, which highlights the importance of analyzing a larger sample of FRBs for a more comprehensive understanding of their properties.

In this paper, we introduce a new interacting mechanism within the dark sector, encompassing both dark energy and dark matter, while grounding our analysis in the familiar framework of the $\mathrm{\Lambda CDM}$ model augmented by baryons and radiation components, including photons and neutrinos. The interaction between dark energy and dark matter is confined to the perturbative level. One significant advantage of this proposal is that all geometric probes yield constraints consistent with the so-called vanilla model or the extended vanilla model, where dark energy has a constant equation of state, $w_{x}$. However, the introduction of this new interacting mechanism affects several theoretical signatures, involving contrast dark matter and dark energy densities. We perform an exploratory analysis of those effects in the CMB power spectra, matter-power spectra, and redshift space distortions. For instance, it allows for a decrease/increment in the integrated Sachs-Wolfe (ISW) effect depending on the value taken by the interaction coupling. This effect could be observationally detected by looking for a cross-correlation between the ISW temperature fluctuations and the distribution of galaxies or quasars. At late times, the interaction in the dark sector becomes very effective, affecting the non-linear scale of structure formation. We discuss how the estimators $f\sigma_{8}(z)$ and $S_{8}(z)$ are affected by different interacting couplings; indicating that $f\sigma_{8}(z)$ can show a relative change of up to $15\%$ compared to the concordance model at low redshifts. Finally, we show how the various terms in the dark energy pressure perturbation (both adiabatic and non-adiabatic) are relevant for different scales, demonstrating the absence of large-scale instabilities.

The intergalactic medium (IGM) underwent intense heating that resulted in pressure disequilibrium in the wake of ionization fronts during cosmic reionization. The dynamical relaxation to restore pressure balance may have driven small-scale turbulence and, hence, the amplification of intergalactic magnetic fields. We investigate this possibility using a suite of $\approx 100$ pc resolution radiation-hydrodynamics simulations of IGM gas dynamics. We show that as the spatial resolution improves beyond that achieved with most prior studies, much of the IGM becomes turbulent unless it was pre-heated to $\gg 100~$K before reionization. In our most turbulent simulations, we find that the gas energy spectrum follows the expected $k^{-5/3}$ Kolmogorov scaling to the simulation's resolution, and the eddy turnover time of the turbulence is $< 1$ Gyr at $k \approx 1 ~$kpc$^{-1}$. Turbulence will grow magnetic fields, and we show that the fields grown by reionization-driven turbulence could explain lower limits on IGM B-field strengths from observations of TeV blazars.

We suggest that a gauge theory CP-violating phase could be degenerate with a magnetic dual of a $4$-form flux. Discrete discharge of this flux by membrane nucleations could reduce the total CP-violating phase to below $10^{-10}$ well before BBN if the charge and the tension of the membranes are in the $\sim keV$ range.

The Stochastic Gravitational Wave Background (SGWB) from cosmic superstrings offers one of the few known possibilities to test String Theory within current experimental reach. However, in order to be compatible with the existing constraints, the tension of a cosmic superstring network is required to lie several orders of magnitude below the Planck scale. This is naturally realized in string compactifications where the volume of the extra dimensions is parametrically large (in string units). We estimate the GW spectrum arising from cosmic superstrings in such scenarios, providing analytical formulae as well as numerical results. Crucially, we do so within a fully-fledged string cosmology, taking into account various modified cosmological epochs (such as kination or early matter domination) induced by the presence of moduli and a time-dependent string tension. We show that part of the spectrum generically lies within reach of LISA and ET, with a large class of models predicting a characteristic drop in the amplitude which may be robustly probed by LISA. The corresponding signal would encode information on the dynamics of moduli and reheating. On the other hand, the ultra-high frequency part of the spectrum can be significantly enhanced by a long, early phase of kination with time-varying tension, yielding a spectral index unique to this set-up.

We analyse the large-scale angular clustering of quasars in the Gaia-unWISE quasar catalog, Quaia, and their cross-correlation with maps of the lensing convergence of the Cosmic Microwave Background (CMB), to constrain the level of primordial non-Gaussianity (PNG). Specifically, we target the scale-dependent bias that would be induced by PNG on biased tracers of the matter inhomogeneities on large scales. The Quaia sample is particularly well suited for this analysis, given the large effective volume covered, and our ability to map out the main potential sources of systematic contamination and mitigate their impact. Using the universality relation to characterise the response of the quasar overdensity to PNG ($p_\phi=1$), we report constraints on the local-type PNG parameter $f_{\rm NL}$ of $f_{\rm NL}=-20.5^{+19.0}_{-18.1}$ (68\% C.L.) by combining the quasar auto-correlation and its cross-correlation with CMB lensing in two tomographic redshift bins (or $f_{\rm NL}=-28.7^{+26.1}_{-24.6}$ if assuming a lower response for quasars, $p_\phi=1.6$). Using the CMB lensing cross-correlations alone, we find $f_{\rm NL}=-13.8^{+26.7}_{-25.0}$. These are the tightest constraints on $f_{\rm NL}$ to date from angular clustering statistics and cross-correlations with CMB lensing.

The minimal warm inflation scenario proposed in Ref. [1] -- featuring an axion-like inflaton coupled to Standard Model (SM) gluons via the standard interaction $\phi G \tilde G$ -- offers a compelling bridge between inflationary dynamics and SM particle content. While the model retains only the inflaton as a beyond-SM field, its original analysis relied on some approximate treatments of warm inflation's (WI) dynamics. Here, we revisit this scenario using WI2easy, a precision computational tool for WI dynamics [2], to rigorously evaluate the model's viability and full range of model's parameters compatible with the observational parameters. Overall, we find that the results of Ref. [1] hold, but with significant differences in the weak and strong dissipative regimes of WI.

Un-doing the effect of gravitational lensing on the Cosmic Microwave Background ('de-lensing') is essential in shaping constraints on weak signals limited by lensing effects on the CMB, for example on a background of primordial gravitational waves. Removing these anisotropies induced by large-scale structures from the CMB maps also generally helps our view of the primordial Universe, by sharpening the acoustic peaks and the damping tail. However, delensing does transfer parts of these anisotropies to the noise maps. This will induce a new large scale 'mean-field' bias to any anisotropy estimator applied to the delensed CMB, and this bias directly traces large-scale structures. This paper analytically quantifies this delensed noise mean-field and its impact on quadratic (QE) and likelihood-based lensing estimators. We show that for Simons-Observatory-like surveys, this mean-field bias can reach 15% in cross-correlation with large-scale structures if unaccounted for. We further demonstrate that this delensed noise mean-field can be safely neglected in likelihood-based estimators without compromising the quality of lensing reconstruction or $B$-mode delensing, provided the resulting lensing map is properly renormalized.