arXiv subjects

Arunansu Sil

Publications and source records attributed to Arunansu Sil.

At least 19 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↗

arXiv2025

Probing Right Handed Neutrino assisted Reheating with Gravitational Waves and Leptogenesis

We investigate a non-instantaneous reheating period in the early Universe, where the inflaton field decays exclusively to right-handed neutrinos (RHNs). The subsequent decay of these RHNs into Standard Model particles not only drives the transition to a radiation-dominated era but also generates the baryon asymmetry of the Universe via leptogenesis. In this typical reheating scenario, gravitational waves (GWs) can be produced during inflaton decay, both through bremsstrahlung and inflaton scattering processes. While GW production via bremsstrahlung dominates near the end of the reheating phase, inflaton scattering leads to a non-negligible GW contribution near the maximum temperature of the Universe. The combined GW spectrum from both decay and scattering processes lies within the sensitivity range of proposed resonant cavity experiments. This framework thus offers a compelling and unified approach to addressing neutrino mass generation, the baryon asymmetry of the Universe via leptogenesis, and probing the dynamics of a non-instantaneous reheating era.

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

Exploring Leptogenesis, WIMP Dark Matter, and Gravitational Waves in an extended Scalar Framework

We explore extensions of type I seesaw framework with a scalar mediator ($Φ$) connecting to a complex scalar dark field ($S$), and right handed neutrinos ($N_i$), with an aim to correlate neutrino mass generation, leptogenesis, and dark matter. $\mathcal{Z}_4\times CP$ turns out to be a phenomenologically viable choice of the extended symmetry, which can accommodate a dimension five effective interaction $\bar{l}_L^α\tilde{H}ΦN_i$, involving the SM lepton isodoublet ${l}_L$, and Higgs $H$; prohibiting the canonical Yukawa term $\bar{l}_L^α\tilde{H} N_i$. The $\mathcal{Z}_{4}$ symmetry is spontaneously broken via the vacuum expectation value (VEV) of the $Φ$ filed, which directly affects neutrino mass generation and leptogenesis; while the $CP$ symmetry stabilises one component of $S$, making it a viable dark matter candidate. The discrete symmetry breaking creates domain wall, which needs to be annihilated before the over-closure of the Universe. This paves the way for gravitational wave signal associated with the model set up, which probes the symmetry breaking scale, and indirectly connects to the other phenomena.

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

Probing ALP-portal fermionic dark matter at the $e^+e^-$ colliders

Axion-like particles (ALPs) are promising candidates for mediating interactions between a dark sector and the Standard Model (SM). In this work, considering the effective interactions of ALPs with the SM gauge bosons and a fermion dark matter (DM), we explore the DM relic satisfied parameter space and assess its testability through indirect searches. The effect of early kinetic decoupling is also discussed in the resonant regime. The potential of probing such ALP-portal fermionic DM at the electron-positron colliders is investigated with the mono-photon plus missing energy final states. We show that a spectacular distinction between the signal and SM background is possible via the missing energy variable, the seed of which lies in the ALP-photon interaction, which also governs the relic density of DM. We further discuss the sensitivity of ALP-photon coupling using the $\chi^2$ analysis at the future electron-positron collider specifications.

hep-ph↗

arXiv2025

Leptogenesis with Majoron Dark Matter

We discuss a model of neutrino mass based on the type I seesaw mechanism embedded in a spontaneously broken global lepton number framework with a $Z_2$ symmetry. We show that the resulting Majoron is a viable freeze-in dark matter candidate. Two right-handed neutrinos are assumed to have dominant off-diagonal masses suggesting resonant leptogenesis as the origin of baryon asymmetry of the Universe. Explicit higher dimensional lepton number violating operators, are shown to play a crucial role in simultaneously controlling both the Majoron production in the early Universe and the right handed neutrino mass splitting relevant for resonant leptogenesis. We perform a combined analysis of Majoron dark matter and leptogenesis, discussing the relative importance of self energy and vertex contributions to CP asymmetry, and explore the parameter space, leading to an intricate relation between neutrino mass, dark matter and baryon asymmetry.

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.

hep-ph↗

arXiv2024

Spontaneous Leptogenesis with sub-GeV Axion Like Particles

A derivative coupling of an axion like particle (ALP) with a B-L current may lead to the baryon asymmetry of the universe via spontaneous leptogenesis provided a lepton number breaking interaction prevails in thermal equilibrium. Conventionally, such scenario works only for heavy ALPs and high reheating temperature due to the fact that the same lepton number breaking contribution is tied up with neutrino mass generation also. In this work, we propose inert Higgs doublet assisted lepton number violating operator to relieve such tension so as to generate lepton asymmetry (of freeze-in/out type) with a much lower reheating temperature that can accommodate light (sub-GeV) ALPs sensitive to current and future ALP searches.

hep-ph↗

arXiv2024

Probing leptogenesis and the minimal neutrino seesaw mechanism through gravitational waves

We propose that a gravitational wave can be generated during leptogenesis in the early Universe which occurs during heavy right-handed neutrino decay. Such a gravitational wave, as remnant of leptogenesis, is shown to be associated with distinguishing signatures that not only act as a powerful probe to leptogenesis but also to the existence of heavy seesaw states which otherwise remain difficult to validate despite its success in explaining the baryon asymmetry of the Universe, closely connected to the origin of neutrino mass.

hep-ph↗

arXiv2024

Towards a more complete description of hybrid leptogenesis

Hybrid leptogenesis framework combining type I and type II seesaw mechanism for neutrino mass necessarily include scattering topologies involving both the scalar triplet and the right handed neutrino. We demonstrate that a systematic inclusion of these mixed scatterings can significantly alter the evolution of the number densities exhibiting up to a factor ten deviation in the predicted asymmetry as demonstrated by our benchmark scenarios. We provide quantitative constraints on the degeneracy of the seesaw scales where the complete analysis becomes numerically significant, limiting the validity of leptogenesis being dominated by the lightest seesaw species only.

hep-ph↗

arXiv2024

Effects of Electroweak Symmetry Breaking on Axion Like Particles as Dark Matter

Axion like particles (ALPs), the pseudo Nambu-Goldstone bosons associated to the spontaneous breaking of global symmetry, have emerged as promising dark matter candidates. Conventionally, in the context of misalignment mechanism, the non-thermally produced ALPs happen to stay frozen due to Hubble friction initially and at a later stage, they begin to oscillate (before matter-radiation equality) at characteristic frequencies defined by their masses and behaving like cold dark matter. In this work, we study the influence of electroweak symmetry breaking (EWSB), through a higher order Higgs portal interaction, on the evolution of ALPs. Such an interaction is found to contribute partially to the ALP's mass during EWSB, thereby modifying oscillation frequencies during EWSB as well as impacting upon the existing correlation between the scale of symmetry breaking and their masses. The novelty of the work lies in broadening the relic satisfied parameter space so as to probe it in near future via a wide range of experiments.

hep-ph↗

arXiv2024

Effects of Reheating on Charged Lepton Yukawa Equilibration and Leptogenesis

We show that the process of non-instantaneous reheating during the post-inflationary period can have a sizable impact on the charged lepton Yukawa equilibration temperature in the early Universe. This suggests relooking the effects of lepton flavors in the leptogenesis scenario where the production and decay of right-handed neutrinos take place within this prolonged era of reheating. We find this observation has the potential to shift the flavor regime(s) of leptogenesis compared to the standard thermal scenario.

hep-ph↗

arXiv2023

Majorons Revisited: light dark matter as FIMP

We show that Majoron, the pseudo-Nambu-Goldstone boson resulting from the spontaneous breaking of global lepton number symmetry, can present itself as a viable freeze-in type of dark matter in a mass range keV-GeV, thanks to the explicit higher dimensional Lepton number breaking operator. Interestingly, the proposal is restricted within the simplest extension of the Standard Model with two singlet right-handed neutrinos and a singlet scalar so to address light neutrino mass and spontaneous breaking of lepton number symmetry respectively. The desired amount of Majoron production takes place from the annihilations of right-handed neutrinos indicating an intriguing connection between neutrino physics and dark matter.

hep-ph↗

arXiv2023

Flavor Leptogenesis During Reheating Era

Recently, it has been shown that the presence of a non-instantaneous era of reheating can significantly alter the charged lepton(s) equilibration temperature(s) which plays important role in flavor leptogenesis. In this work, we extend the analysis to a more general situation where RHNs are also produced from the decay of the inflaton. The presence of these RHNs along with the thermally generated ones (above its mass equivalent temperature only) redistributes different components of the energy density of the Universe during this reheating era, thereby affecting the charged lepton equilibration temperature (in addition to the Hubble effect) as well as the final reheating temperature $T_{\rm{RH}}$. Taking both the effects into account, we find that the decay of the lightest RHN in the set-up not only provides a platform to study flavor leptogenesis during reheating, but also an interesting framework of $quasi$-thermal leptogenesis emerges.

hep-ph↗

arXiv2022

Symmetry origin of Baryon Asymmetry, Dark Matter and Neutrino Mass

We propose a minimal model based on lepton number symmetry (and violation), to address a common origin of baryon asymmetry, dark matter and neutrino mass generation. The model consists of a vector like fermion to constitute the dark sector, three right handed neutrinos (RHN) to dictate leptogenesis and neutrino mass, while an additional complex scalar is assumed to be present in the early universe the decay of which produces both DM and RHN via lepton number violating and lepton number conserving interactions respectively. Interestingly, the presence of the same scalar helps in making the electroweak vacuum stable till the Planck scale. The unnatural largeness and smallness of the parameters required to describe correct experimental limits are attributed to lepton number violation. The allowed parameter space of the model is illustrated via a numerical scan.

hep-ph↗

arXiv2022

Two Component Doublet-Triplet Scalar Dark Matter stabilising the Electroweak vacuum

A two-component scalar DM scenario comprising an additional scalar doublet and a $Y$ = 0 scalar triplet is proposed. Key features of the ensuing dark matter phenomenology are highlighted with emphasis on inter-conversion between the two dark matter components. For suitable choices of the model parameters, we show that such inter-conversion can explain the observed relic abundance when the doublet dark matter component has mass in the \emph{desert} region while the triplet component has sub-TeV mass. This finding is important in the context of such mass regions known to predict under-abundant relic for the standalone cases of the scalar doublet and triplet. In addition, we also show that the present scenario can stabilise the electroweak vacuum up to the Planck scale in the parameter space responsible for the requisite dark matter observables.

hep-ph↗