arXiv subjects

Shibsankar Si

Publications and source records attributed to Shibsankar Si.

4 recordsLinked to original sources

arXiv2026

Constraining Primordial Black Holes via p-wave annihilation in light of CMB Spectral Distortion and 21-cm global signal

Primordial black holes (PBHs) can form spike density halos through the accretion of weakly interacting massive particles (WIMPs). In these halos, the enhanced density significantly boosts the annihilation rate of WIMPs. For Majorana dark matter annihilation into light fermions, the s-wave part of the annihilation cross section is helicity-suppressed, making the p-wave contribution dominant. We study the velocity-dependent p-wave annihilation case, whose resulting energy injection can modify the thermal and ionization history of the Universe, leaving observable imprints on the cosmic microwave background (CMB) spectrum and the global 21-cm signal. From the predicted energy injection into the plasma, we derive stringent upper limits on the fraction of dark matter in form of PBHs for p-wave annihilation models, based on the observational constraints of the CMB spectral distortions ($y$-type), and from the measurement of the 21-cm absorption signal at cosmic dawn. Our results highlight that accounting for the p-wave nature of annihilation is crucial for deriving robust constraints on the PBH abundance.

astro-ph.CO↗

arXiv2025

Constraining self-interacting ultrahigh-energy muon neutrinos by cosmic microwave background spectral distortion

The neutrino telescopes have firmly established the existence of ultrahigh-energy neutrinos. Observations of these neutrinos offer a unique probe of neutrino self-interactions. This work investigates how the self-interacting neutrinos, mediated by scalar bosons, inject energy into the medium through radiative scattering with the cosmic neutrino background, leaving an imprint on the cosmic microwave background (CMB) spectrum. The energy injection into plasma in redshift ranges, $5\times10^4\lesssim z\lesssim2\times10^6$ and $ z\lesssim5\times10^4$, leads to $\mu$-type and $y$-type CMB spectral distortions, respectively. Using observational constraints from Cosmic Background Explorer/Far Infrared Absolute Spectrophotometer (COBE/FIRAS) and projected sensitivities from Primordial Inflation Explorer (PIXIE) experiments for $\mu$-type and $y$-type CMB distortions, we derive the stringent upper bounds on the self-interaction coupling strength as a function of mediator mass for neutrino interactions. We focus on flavor-specific self-interaction related to muon neutrinos and sub-GeV mass mediators ($m_{\phi}$). We find the upper bound on the self-interaction coupling strength to be $\sim 2.8\times 10^{-4}$ for the muon neutrino, considering ultrahigh-energy muon neutrino energy to be 1 PeV and PIXIE projected upper bounds on $y$-type CMB spectral distortion. The bound remains constant till the mediator mass reaches the center-of-mass energy, and after that, it gets relaxed and becomes proportional to the mediator mass. We have also compared our results with existing bounds in the literature. Our findings indicate that CMB spectral distortion could play a decisive role in exploring neutrino physics beyond the standard model of particle physics, and future missions like PIXIE can provide valuable insights.

astro-ph.CO↗

arXiv2025

Revisiting constraints on superconducting cosmic strings in light of Dark Ages global 21-cm signal

The Superconducting Cosmic Strings (SCS) are a special case of cosmic strings that have a core carrying a charged field. When SCS passes through magnetized regions, the charged particles in the string experience a Lorentz force, which can produce radiation on the entire electromagnetic spectrum. This radiation can inject energy into the surrounding plasma, resulting in a modification of the thermal and ionization evolution of the intergalactic medium (IGM) and, subsequently, the global 21-cm signal. The signatures of SCS in the post-recombination era have been primarily studied in the low-frequency (radio) regime, which does not impact the state of the IGM. In this work, we study the effect of decaying SCS on the dark ages global 21-cm signal $(\delta T_b)$, considering both the ionizing and radio radiation. The dark ages signal can provide pristine cosmological information free from astrophysical uncertainties, as the universe was primarily homogeneous during this era in the absence of baryonic structure formation. Considering a change in the $\delta T_b$ at redshift $z\sim 89$ from the $\Lambda \rm CDM$ framework, we derive an upper bound on the decay efficiency parameter, $g\equiv g(I,~G\mu_s)$, to be $\lesssim 5.1\times10^{14}\, \rm GeV^2$, where, $I$ and $G\mu_s$ represent the loop current and string tension of SCS, respectively.

astro-ph.CO↗

arXiv2024

Constraining Viscous Dark Matter in light of CMB Spectral Distortion

We calculate the $μ$- and \textit{y}-type spectral distortions of Cosmic Microwave Background (CMB), taking a non-standard interaction between baryons and viscous dark matter. Using the CMB spectral distortion observations, we can constrain any exotic mechanism that may change the energy of the CMB photon, leading to a CMB spectrum distortion. Depending on the viscosity of dark matter, the energy transfer between dark matter and baryons may modify, leading to a modification in CMB distortion. The existing Cosmic Background Explorer (COBE)/FIRAS and the Primordial Inflation Explorer (PIXIE) set limits on \textit{y} and $μ$ types of distortions to $y = 1.5\times10^{-5}$, $μ= 9.0\times10^{-5}$ and $y = 10^{-8}$, $μ= 5.0\times10^{-8}$, respectively. In this paper, we discuss the pre-recombination contributions to $μ$ and \textit{y}-type distortions by viscous dark matter and constrain the parameter space using PIXIE bounds on spectral distortion.

astro-ph.CO↗