arXiv subjects

Arnab Chaudhuri

Publications and source records attributed to Arnab Chaudhuri.

At least 19 recordsLinked to original sources

arXiv2026

Leptogenesis and Planck-scale black hole remnants in a Pati-Salam cosmology

We study leptogenesis and Planck-scale remnant dark matter from primordial black hole (PBH) evaporation in a minimal Pati-Salam cosmology, with the gauge symmetry broken before inflation so that magnetic monopoles are diluted away. A singlet inflaton with a near-inflection potential enhances the curvature power spectrum on small scales, producing a narrow black hole population that briefly dominates the energy density. The Pati-Salam embedding ties the right-handed neutrino masses to the SU(2)_R breaking scale, and cosmological consistency forces both the scalar-sector Yukawa coupling and the heavy neutrino mass well below that scale. Two regimes emerge, depending on whether the black holes are hot enough to emit the lightest right-handed neutrino. Lighter PBHs drive non-thermal leptogenesis, while heavier ones require a thermal asymmetry and also affect it through entropy dilution. If quantum gravitational backreaction halts evaporation at the Planck scale, each PBH leaves a stable remnant whose present abundance scales as the inverse five-halves power of the initial mass. Suppressing remnants requires heavier black holes, but the lighter PBHs needed for non-thermal leptogenesis overproduce remnant dark matter. Thus, remnant dark matter and non-thermal leptogenesis are mutually exclusive. When the thermal contribution is included, a single initial PBH mass near 10^6 g accommodates the observed dark matter abundance, the heavy neutrino mass required by the baryon asymmetry, and the Pati-Salam breaking scale. The scenario predicts a stochastic gravitational wave background from Poisson fluctuations of the black hole distribution, within reach of future experiments, alongside high-frequency graviton emission constrained by future measurements of the effective number of relativistic species.

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arXiv2026

Gravitational Wave Signatures of $\mathrm{U(1)_X}$ Breaking and Right-Handed Neutrino Dynamics

The Standard Model (SM) leaves several fundamental questions unanswered, including the origin of neutrino masses, the baryon asymmetry of the Universe, and the nature of dark matter. Motivated by these gaps, we investigate an extension of the SM with an additional local $U(1)_X$ gauge symmetry and a complex scalar singlet that spontaneously breaks this symmetry via its vacuum expectation value. The extended framework naturally accommodates three right-handed neutrinos (RHNs) to ensure anomaly cancellation and implements a type-I seesaw mechanism for active neutrino masses. We utilized Casas-Ibarra parameterization to systematically reconstruct the Yukawa coupling matrix which automatically satisfy the observed neutrino data. Furthermore, we estimate the key parameters of the first-order phase transition and compute the resulting stochastic gravitational wave spectrum, demonstrating that it can lie within the reach of forthcoming experiments such as LISA, DECIGO, BBO, and the Einstein Telescope. The right-handed neutrinos also open a viable path for thermal leptogenesis, providing a unified link between neutrino mass generation, baryogenesis, and gravitational wave signatures. Our results demonstrate that this minimal $U(1)_X$ scenario remains a promising probe for physics beyond the Standard Model, accessible through upcoming gravitational wave and neutrino experiments.

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arXiv2026

Non-Markovian Electroweak Baryogenesis: Memory Effects on CP-Violating Transport and Gravitational Waves

We develop a non-Markovian extension of electroweak baryogenesis within the Schwinger--Keldysh real-time effective field theory framework and the Kadanoff--Baym hierarchy. When the relaxation time of CP-violating mediators becomes comparable to the bubble-wall crossing time, transport dynamics acquire temporal nonlocality, leading to memory-kernel corrections to the CP-violating source and diffusion equations beyond the Markovian approximation. These effects shift the optimal wall velocity to smaller values, narrow the viable parameter space, and induce a characteristic non-monotonic dependence of the baryon asymmetry on the memory timescale for sub-optimal wall velocities, which cannot be reproduced by a consistent Markovian reparameterisation. A systematic parameter analysis identifies regions compatible with the observed baryon asymmetry and constrains the allowed memory timescale from hydrodynamic stability and the physical range of the CP-violating phase. We also assess the correlated impact on the stochastic gravitational-wave signal, finding that memory effects can enhance the effective source duration and amplitude, although much of the viable parameter space remains below near-future detector sensitivities and theoretical uncertainties remain at the order-of-magnitude level. These results establish non-Markovian transport as a well-motivated extension of electroweak baryogenesis and introduce the memory timescale as a parameter testable through baryon asymmetry measurements, collider CP probes, and gravitational-wave observations.

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arXiv2026

Memory-Burden Suppression of Hawking Radiation and Neutrino Constraints on Primordial Black Holes

We investigate the impact of quantum gravitational memory-burden effects on high-energy neutrino signals from evaporating primordial black holes and the resulting constraints from IceCube observations. Treating the backreaction as an energy-dependent deformation of the Hawking emission spectrum, we show that the high-energy tail is suppressed while the infrared behaviour remains unchanged. We derive analytically that this modification reduces the total luminosity and extends the evaporation lifetime by a mass-independent factor determined solely by the suppression parameter. Using an effective treatment of cosmological redshift, we compute the diffuse neutrino flux from a primordial black hole population and compare it with the observed astrophysical neutrino spectrum to constrain the primordial black hole dark matter fraction. We find that the suppression onset lies within the IceCube sensitivity window, leading to a direct reduction of the observable signal and a systematic weakening of the inferred bounds. Our results provide a controlled phenomenological framework for assessing the impact of quantum gravitational corrections on neutrino probes of primordial black hole evaporation.

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arXiv2026

Neutrino Fluence influenced by Memory Burdened Primordial Black Holes

We study the impact of quantum gravitational memory burden - a backreaction effect that suppresses black hole evaporation - on neutrino signals from primordial black holes (PBHs). This suppression, modeled via a parameter k, reduces the high-energy muon neutrino fluence, particularly during the late stages of evaporation. We also consider beyond the Standard Model scenarios in which heavy neutral leptons (HNLs) are emitted by PBHs and subsequently decay, injecting secondary neutrinos that partially mitigate the suppression in the MeV-GeV range. We compute the full time-integrated neutrino spectrum and evaluate the expected IceCube event rates across the (k, mN) parameter space. We analyze both single source burst scenarios and the cumulative Galactic contribution assuming PBHs trace a realistic dark matter halo distribution. Even under optimistic proximity assumptions, the predicted event rates remain far below IceCube sensitivity, and population-level stacking within current observational bounds on the PBH abundance does not yield an observable signal in the considered mass range for PBH abundances consistent with existing observational constraints. These results demonstrate that entropy-suppressed evaporation substantially weakens neutrino detectability of light PBHs and must be consistently incorporated in future multi-messenger searches.

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arXiv2026

Dark Temperature Hierarchies and Gravitational Waves from the Electroweak Phase Transition

We investigate the impact of a semi-decoupled dark sector with a temperature hierarchy relative to the Standard Model plasma on the electroweak phase transition and its associated gravitational wave signal. Working within a minimal Higgs-portal extension, we allow the dark sector to possess a higher temperature at the electroweak epoch while remaining consistent with cosmological bounds on additional relativistic degrees of freedom. The temperature hierarchy modifies the thermal structure of the effective potential and alters nucleation dynamics without requiring large portal couplings or extreme supercooling. Within the cosmologically allowed window, we find a monotonic enhancement of the gravitational wave amplitude by more than an order of magnitude compared to the standard thermal case, accompanied by a shift of the peak frequency within the millihertz regime. The resulting stochastic background moves substantially closer to the projected sensitivity of future space-based interferometers. Our results demonstrate that hidden-sector temperature hierarchies can leave observable imprints on electroweak-scale phase transitions even in minimal and perturbative frameworks.

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arXiv2026

Primordial black hole evaporation in a thermal bath and gravitational waves

Primordial black holes (PBHs) formed in the early Universe evaporate via Hawking radiation and constitute a generic source of stochastic gravitational waves. Existing studies of gravitational wave production from evaporating PBHs typically assume vacuum evaporation, neglecting the fact that PBHs in the early Universe are embedded in a hot thermal plasma. In this work, we investigate gravitational wave production from primordial black holes whose evaporation is thermally influenced by their surrounding environment. We adopt a thermal evaporation framework in which interactions with the ambient plasma modify the effective decay rate of the black hole, leading to enhanced mass loss at early times and a redistribution of the evaporation history compared to the standard non-thermal vacuum case. Since graviton emission is intrinsically tied to the evaporation history of PBHs, these thermal effects play a crucial role in determining the timing and spectral properties of the resulting stochastic gravitational wave background. Our results provide a consistent framework for incorporating thermal effects into gravitational wave production from evaporating primordial black holes and set the stage for a detailed analysis of their observational signatures.

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arXiv2026

Gravitational Waves from First-Order Phase Transitions Assisted by Temperature-Enhanced Scatterings

Scatterings whose cross sections increase as the cosmic temperature decreases, known as temperature - enhanced scatterings, can have a significant impact on the thermal effective potential of scalar fields responsible for driving cosmological first-order phase transitions. We show that such effects naturally manifest as finite-temperature self-energy corrections to the scalar mass term, leading to an additional contribution of the form $c\,T^{p}ϕ^{2}$ in the effective potential. In this work, we systematically investigate how these loop-induced, temperature-dependent corrections affect key phase transition parameters, including the nucleation temperature, latent heat release, and inverse duration parameter. These modifications influence both the strength and duration of the phase transition, which in turn determine the properties of the resulting stochastic gravitational-wave (GW) background. Employing semi-analytic computational methods, we evaluate the GW spectra generated under these conditions and compare our predictions with the projected sensitivities of forthcoming detectors such as LISA, DECIGO, and BBO. Our analysis demonstrates that finite-temperature scattering effects of this kind can substantially strengthen first-order transitions and produce GW signals that lie within the reach of future observational facilities. The results establish a concrete thermal-field-theoretic origin for temperature-dependent modifications of the scalar potential and emphasize their importance in shaping early-Universe cosmological signatures.

astro-ph.CO↗

arXiv2025

Electroweak Phase Transition, Gravitational Waves and Collider Probes in Multi-Scalar Dark Matter Scenarios

We study scalar singlet extensions of the Standard Model (SM), focusing on scenarios where dark matter (DM) is stabilized by a $\mathbb{Z}_2$ symmetry. In the minimal single-scalar extension of the SM, only a narrow region near the Higgs resonance remains viable, requiring small portal couplings in order to simultaneously satisfy the observed relic abundance and comply with the most recent direct detection limits from the LUX-ZEPLIN (LZ-2024) and XENON1T experiments. To address this limitation, we extend the dark sector by introducing additional real singlet scalars. In both two- and three-singlet extensions, we demonstrate that the observed dark matter relic density can be accommodated with larger Higgs portal couplings. These couplings significantly impact early-Universe dynamics by enhancing the strength of the electroweak phase transition. Both the two- and three-singlet scalar extensions can induce a strong first-order electroweak phase transition, generating stochastic gravitational waves potentially observable at future space-based detectors such as LISA and DECIGO. Notably, the three-singlet scenario induce an even stronger transition compared to the two-singlet case, enhancing the gravitational wave signal strength. Our results highlight the potential of extended scalar sectors as testable frameworks connecting dark matter and gravitational wave signals.

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arXiv2025

EFT of Non-Markovian $U(1)_X$ Breaking: Dark Matter and Gravitational Waves

We develop an effective field theory (EFT) framework for $U(1)_X$ gauge symmetry breaking in which the dynamics of the order parameter acquire non-local-in-time (``memory'') corrections from a heavy dark sector. Integrating out metastable or slowly equilibrating fields generates temporal kernels in the EFT, yielding a history-dependent effective potential for the $U(1)_X$ scalar. These non-Markovian terms qualitatively alter first-order phase transition dynamics by modifying bubble nucleation, latent heat release, and wall propagation. The resulting stochastic gravitational-wave spectrum exhibits distinctive features such as broadened peaks, asymmetric slopes, and possible secondary ``echoes'' that are absent in conventional Markovian treatments. When the memory-generating sector also participates in dark matter production, the same kernel parameters correlate gravitational-wave signatures with the relic abundance. This work establishes the EFT formalism for non-equilibrium symmetry breaking and highlights testable predictions for upcoming GW observatories and DM searches.

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arXiv2025

Anisotropic Neutrino Emission from Spinning, Moving, and Charged Primordial Black Holes

The angular and spectral features of neutrinos emitted from primordial black holes (PBHs) carry key imprints of the black hole's fundamental properties. This work investigates the directional emission of neutrinos from Kerr-Newman PBHs undergoing Hawking evaporation, accounting for the combined effects of spin, motion, and electric charge. Rotation induces anisotropic fluxes through axisymmetric geometry and spin-dependent greybody factors, while relativistic motion leads to pronounced Doppler beaming along the direction of travel. Electric charge modifies the thermodynamic evolution and suppresses the emission of like-charged particles, altering the overall spectrum and burst duration. The resulting neutrino flux exhibits rich angular structure, energy dependence, and time profiles that vary with PBH parameters. These directional signatures enhance the prospects for detection at current and future neutrino observatories, and offer new multi-messenger probes of PBH populations in the early universe.

astro-ph.CO↗

arXiv2025

Directional Neutrino Bursts from Spinning and Moving Primordial Black Holes

We show that primordial black holes (PBHs) with significant spin and bulk motion produce sharply collimated neutrino bursts from Hawking evaporation, arising from the interplay of spin-induced angular anisotropy and relativistic Doppler boosting. This effect shifts the neutrino spectrum into the multi-GeV to hundreds of GeV range, where atmospheric backgrounds drop steeply, and enhances the flux by orders of magnitude within a narrow forward cone. We compute the full lab-frame neutrino distribution and derive updated constraints on PBH number density from non-observation of such bursts in IceCube and KM3NeT. Our results identify directional high-energy neutrino bursts as a distinctive, testable signature of spinning PBHs, providing a complementary probe of the PBH dark matter hypothesis and Hawking radiation.

astro-ph.CO↗

arXiv2025

New bounds on Memory Burdened Primordial Black Holes from Big Bang Nucleosynthesis

Primordial black holes (PBHs) with masses below $10^9\,\rm{g}$ are typically assumed to have negligible cosmological impact due to their rapid evaporation via Hawking radiation. However, the 'memory burden' effect, which is a quantum suppression of PBH evaporation, can dramatically alter their decay dynamics. In this work, we revisit early-Universe constraints on ultralight PBHs in this mass range, demonstrating that memory burden significantly alters previous constraints. We compute new cosmological bounds from BBN that strongly limit the presence of ultralight PBHs in the early Universe. We report that the PBHs in the mass range $10^0$-$10^2\,\rm{g}$ for $k=2$ are unconstrained by observations.

astro-ph.CO↗

arXiv2025

Neutrino Portal to Extra Dimensions: Unified Origin of Dark Radiation, Dark Matter, and Neutrino Decay

We propose a unified framework based on sterile neutrinos propagating in large extra dimensions (LED) and coupled to a pseudo-Nambu-Goldstone boson (Majoron) arising from spontaneous lepton number violation. In this setup, the lightest Kaluza-Klein (KK) sterile neutrino serves as warm dark matter, higher KK modes decay invisibly producing a relativistic Majoron contributing to the effective number of neutrino species (Delta Neff), and active neutrinos undergo invisible decay. This model addresses dark radiation, dark matter, and neutrino anomalies within a minimal, testable framework. We present the Boltzmann evolution of relevant species, identify the viable parameter space, and highlight implications for CMB-S4, Lyman-alpha, and neutrino observatories.

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arXiv2024

Dark Matter from Evaporating Primordial Black Holes in the Early Universe

Primordial Black Holes (PBH) could dominate in the early universe and, evaporating before Big bang Nucleosynthesis, can provide new freeze in mechanism of dark matter (DM) production. The proposed scenario is considered for two possible mechanisms of PBH formation and the corresponding continuous PBH mass spectra so that the effect of non-single PBH mass spectrum is taken into account in the results of PBH evaporation, by which PBH dominance in the early universe ends. We specify the conditions under which the proposed scenario can explain production of dark matter in very early Universe.

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arXiv2024

The N2HDM, Entropy Production and Stochastic Gravitational Waves

This study undertakes a reconsideration of the potential for a first-order electroweak phase transition, focusing on the next-to-minimal two Higgs doublet model (N2HDM). Our exploration spans diverse parameter spaces associated with the phase transition, with a particular emphasis on examining the generation of stochastic Gravitational Waves (GW) resulting from this transition. The obtained results are meticulously compared against data from prominent gravitational wave observatories, and the possibility of their detection in the future GW observations have been established. In passing by we analyse the strength of the phase transition through the production of entropy during the electroweak phase transition.

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arXiv2023

Dark matter production from two evaporating PBH distributions

Particulate Dark Matter (DM), completely isolated from the Standard Model particle sector, can be produced in the early universe from Primordial Black Hole (PBH) evaporation. However, Big Bang Nucleosynthesis (BBN) observations put an upper bound on the initial mass of PBH requiring the PBH to evaporate completely before the advent of BBN. DM particles in the mass range $\sim(1-10^9)$ GeV can not explain the observed relic abundance for an early matter dominated universe due to this BBN constraint. However, this assumes the presence of only one monochromatic PBH mass distribution in the early universe. In this work, we explore the simple possibility of achieving the observed relic with DM masses from the above mentioned range for an early matter dominated era with two monochromatic evaporating PBH mass distributions and demonstrate that the fermionic DM masses consistent with BBN change slightly.

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arXiv2022

Study of entropy production due to electroweak phase transition in $Z_2$ symmetric extension of the Standard Model

In this work we consider the simple $Z_2$ symmetric extension to the Standard Model (SM) and proceed to study the nature of electroweak phase transition (EWPT) in the early universe. We show that the nature of the phase transition changes from a smooth crossover in the SM to a strong first order with this addition of the real scalar. Furthermore, we show the entropy release in this scenario is higher than that of the SM. This can lead to a strong dilution of frozen out dark matter particles and baryon asymmetry, if something existed before the onset of the phase transition.

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