arXiv subjects

Shiuli Chatterjee

Publications and source records attributed to Shiuli Chatterjee.

5 recordsLinked to original sources

arXiv2026

Exploring non-equilibrium effects in sequential freeze-in

Freeze-in of multi-component dark sectors is governed not only by the interaction with the thermal plasma, but also by their internal dynamics. Full thermalisation within the dark sector is not guaranteed, raising the question of impact of departures from local thermal equilibrium onto the evolution and ultimately relic abundance and momentum distribution of dark matter. In this work we explore this question in a minimal two-scalar model, which can give rise to observable signatures in indirect detection and long-lived particle searches at forward physics experiments. Focusing on the phenomenologically viable regions, we analyse the impact of non-thermal evolution on the dark matter abundance, finding deviations of up to an order of magnitude between the full phase-space treatment and the traditional number-density approach. Our results highlight the importance of phase-space level computation for accurate freeze-in predictions and further motivate dedicated numerical tools for studying the evolution of multi-component dark sectors at the phase space level.

hep-ph↗

arXiv2025

Conversions in two-component dark sectors: a phase space level analysis

Conversions between the states in the dark sector affect not only their number densities but also their momentum distributions. In this work we study a phenomenologically motivated two-component dark matter scenario, based on the Coy Dark Matter model, in order to quantify the effect of conversions on departure from kinetic equilibrium and consequently the relic abundance. We perform a detailed numerical analysis at the level of the phase space distributions of dark sector particles, implementing all the relevant processes, including conversions, elastic scatterings and annihilations. Focusing on the parameter regions that lead to the observed relic abundance and provide a good fit to the Galactic Centre excess, we find that departure from kinetic equilibrium can alter the predictions for the total abundance by more than $100\%$, while in most of the interesting parameter space being in the range from around $-20\%$ to $50\%$. The effect on each dark matter constituent separately can be much larger, even up to an order of magnitude, which can significantly affect the expected present-day gamma ray flux, and consequently phenomenology of the model.

hep-ph↗

arXiv2022

Faint light of old neutron stars and detectability at the James Webb Space Telescope

Isolated ideal neutron stars (NS) of age $>10^9$ yrs exhaust thermal and rotational energies and cool down to temperatures below $\mathcal{O}(100)$ K. Accretion of particle dark matter (DM) by such NS can heat them up through kinetic and annihilation processes. This increases the NS surface temperature to a maximum of $\sim 2550$ K in the best case scenario. The maximum accretion rate depends on the DM ambient density and velocity dispersion, and on the NS equation of state and their velocity distributions. Upon scanning over these variables, we find that the effective surface temperature varies at most by $\sim 40\%$. Black body spectrum of such warm NS peak at near infrared wavelengths with magnitudes in the range potentially detectable by the James Webb Space Telescope (JWST). Using the JWST exposure time calculator, we demonstrate that NS with surface temperatures $\gtrsim 2400$ K, located at a distance of 10\,pc can be detected through the F150W2 (F322W2) filters of the NIRCAM instrument at SNR\,$\gtrsim 10$ (5) within 24 hours of exposure time. Independently of DM, an observation of NS with surface temperatures $\gtrsim 2500$ K will be a formative step towards testing the minimal cooling paradigm during late evolutionary stages.

astro-ph.HE↗

arXiv2022

Explorations of pseudo-Dirac dark matter having keV splittings and interacting via transition electric and magnetic dipole moments

We study a minimal model of pseudo-Dirac dark matter, interacting through transition electric and magnetic dipole moments. Motivated by the fact that xenon experiments can detect electrons down to $\sim$\,keV recoil energies, we consider $\mathcal{O}$(keV) splittings between the mass eigenstates. We study the production of this dark matter candidate via the freeze-in mechanism. We discuss the direct detection signatures of the model arising from the down-scattering of the heavier state, that are produced in Solar upscattering, finding observable signatures at the current and near-future xenon based direct detection experiments. We also study complementary constraints on the model from fixed target experiments, lepton colliders, supernovae cooling and cosmology. We show that the latest XENONnT results rule out parts of the parameter space for this well motivated and minimal dark matter candidate. Next generation xenon experiments can either discover or further constrain how strongly inelastic dark matter can interact via the dipole moment operators.

hep-ph↗

arXiv2021

Freezing In with Lepton Flavored Fermions

Dark, chiral fermions carrying lepton flavor quantum numbers are natural candidates for freeze-in. Small couplings with the Standard Model fermions of the order of lepton Yukawas are `automatic' in the limit of Minimal Flavor Violation. In the absence of total lepton number violating interactions, particles with certain representations under the flavor group remain absolutely stable. For masses in the GeV-TeV range, the simplest model with three flavors, leads to signals at future direct detection experiments like DARWIN. Interestingly, freeze-in with a smaller flavor group such as $SU(2)$ is already being probed by XENON1T.

hep-ph↗