arXiv subjects

Dipendu Bhandari

Publications and source records attributed to Dipendu Bhandari.

6 recordsLinked to original sources

arXiv2026

First Order Phase Transition Induced Graviton Bremsstrahlung: A Multi Peak Gravitational Wave Signature

Gravitational waves (GWs) from first order phase transitions (FOPTs) are conventionally sourced by bubble collisions, sound waves, and plasma turbulence. We propose a novel microscopic GW source arising from graviton bremsstrahlung during the decay of the scalar field driving the FOPT. In the presence of Yukawa interactions with light fermions, the scalar decay is inevitably accompanied by graviton emission due to the universal coupling of gravity to the energy-momentum tensor. We show that these gravitons generate an additional stochastic GW background during the phase-transition epoch, complementing the conventional FOPT signal. The resulting GW spectrum can exhibit a characteristic multi-peaked structure. Unlike scenarios in which different GW components originate from distinct cosmological epochs, all contributions considered here emerge from the dynamics of the same FOPT, offering a unique probe of both its microscopic particle dynamics and macroscopic plasma evolution.

hep-ph↗

arXiv2026

Imprint of matter-antimatter asymmetry on collapsing domain walls

Spontaneous breaking of discrete symmetries play non-trivial role in many well-motivated particle physics models. However, it leads to a network of cosmologically unwanted domain walls (DWs) which can be made unstable by introducing a bias term in the scalar potential. In this letter, we provide a novel origin of such bias terms at finite temperature due to radiative corrections from a Dirac fermion with large asymmetry $\sim \mathcal{O}(0.1)$ in its number density. In addition to getting a new viable region of parameter space for collapsing DWs not explored previously and resulting gravitational waves (GWs) accessible at future experiments, the viability of the scenario crucially depends on the temperature of asymmetry generation too. This provides a unique way of probing both the amount of asymmetry and the corresponding temperature via future observations of GWs from collapsing DWs. The large asymmetry in the Dirac fermion can also have interesting implications for the observed baryon asymmetry as well as dark matter and large neutrino asymmetry.

hep-ph↗

arXiv2025

Reconciling ALP Dark Matter and Electroweak Baryogenesis through First-Order Electroweak Phase Transition

We show that an axionlike particle (ALP) can simultaneously generate the baryon asymmetry and constitute dark matter through dynamics triggered by a first-order electroweak phase transition (EWPT). In our proposal, the transition briefly reshapes the ALP potential via a temperature-dependent vacuum expectation value of a scalar field $S$, responsible for making the EWPT of first order, inducing a transient mass enhancement of ALP via higher-dimensional $U(1)$-breaking operator(s). This sudden kick generates a large ALP velocity near the onset of EWPT enabling the broadening of relic satisfied parameter space and predict a complementary stochastic gravitational-wave signal from the underlying first-order transition. We further show that the same ALP dynamics can naturally fuel electroweak baryogenesis through its coupling to electroweak anomaly.

hep-ph↗

arXiv2025

Impact of First-order Electroweak Phase Transition on QCD Axion

The QCD axion addresses the strong CP problem and dark matter via the misalignment mechanism, typically requiring a decay constant $f_a\sim \mathcal{O}(10^{12}$ GeV), unless the initial misalignment angle ($θ_i$) is fine-tuned. This work presents a novel approach where the possibility that the QCD axion satisfying the correct relic is extended over a broad range for $f_a\in [10^8, 10^{14}$] GeV without fine-tuning the $θ_i$, by introducing a new phase of axion oscillation dynamics across the electroweak phase transition (EWPT). This mechanism, we call it {\it{recurrent ~misalignment}}, is a result of a non-renormalizable Peccei-Quinn symmetry breaking interaction involving the axion and the sector responsible for making the EWPT of first order. The scenario not only enhances the QCD axion parameter space in terms of its detection possibility, but also provides a unique probe by detectable gravitational waves.

hep-ph↗

arXiv2025

Exploring Leptogenesis in the Era of First Order Electroweak Phase Transition

We present a novel approach for implementing baryogenesis via leptogenesis at low scale within neutrino seesaw framework where a sufficient lepton asymmetry can be generated via out of equilibrium CP-violating decays of right handed neutrinos (RHNs) even when their mass falls below the Standard Model (SM) Higgs mass. It becomes possible by keeping the sphaleron in equilibrium below its conventional decoupling temperature $T_{\rm sp}^{\rm SM} \sim131.7$ GeV in SM so as to facilitate the conversion of lepton asymmetry to baryon asymmetry at such a low scale, thanks to the flexibility of the bubble nucleation temperature in case the electroweak phase transition (EWPT) is of first order. The scenario emerges as an exciting (and perhaps unique) possibility for low scale leptogenesis, particularly if the Universe attains a reheating temperature lower than 131.7 GeV. We show that a stochastic gravitational wave, characteristic of such first order EWPT, may be detected in near future detectors while the presence of RHNs of mass as low as 35 GeV opens up an intriguing detection possibility at current and future accelerator experiments.

hep-ph↗

arXiv2024

Leptogenesis from a Phase Transition in a Dynamical Vacuum

We show that a phase transition may take place in the early Universe at a temperature $T_*$ via a Standard Model singlet scalar field which happens to couple to right handed neutrinos (RHN) resulting a temperature dependent mass for them that finally relaxes to a constant value after electroweak phase transition (EWPT). As a result, a requisite amount of lepton asymmetry can be produced at a temperature close to $T_*$ satisfying the observed baryon asymmetry of the Universe via sphaleron process even when the zero temperature masses of the RHNs fall in sub GeV regime providing a testable scenario for leptogenesis. Interestingly, the framework is also capable of predicting a primordial lepton asymmetry (generated at a temperature below the EWPT), as hinted by helium abundance measuring experiments, bearing a correlation with early phase of leptogenesis.

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