arXiv subjects

Jaydeb Das

Publications and source records attributed to Jaydeb Das.

14 recordsLinked to original sources

arXiv2026

Connecting Vector-like Muons, pNGB Dark Matter and Electroweak Phase Transition through Collider and Gravitational Wave

We study an extension of the Standard Model with two complex scalar singlets, $S_2$ and $S_3$, charged under $\mathbb{Z}_2$ and $\mathbb{Z}_3$, respectively, and a muon-philic vector-like lepton $\psi$ carrying the same $\mathbb{Z}_3$ charge as $S_3$. The pseudoscalar associated with the $\mathbb{Z}_2$ sector remains stable due to the CP symmetry of the potential and serves as the dark matter (DM) candidate, with its mass generated through the corresponding soft breaking of the global $U(1)$ symmetry. The vector-like muon couples to the $\mathbb{Z}_3$ scalar and renders the second pseudoscalar unstable, thereby realizing an effectively single-component pNGB DM scenario. The pNGB nature strongly suppresses the tree-level spin-independent direct-detection cross section, while viable parameter regions reproduce the observed relic abundance and satisfy LHC monojet constraints. We further compute the one-loop contribution to DM-nucleon scattering and find that the resulting cross section remains below current experimental limits while being potentially accessible to future direct-detection experiments. At a multi-TeV muon collider, scalar mediated $ t$-channel processes can significantly enhance vector-like-muon pair production. We perform a detailed multivariate analysis for a future muon collider at 3 TeV center-of-mass energy. We also identify viable benchmark points exhibiting strong first-order electroweak phase transitions (SFOEWPT) with successful bubble nucleation, which can generate potentially observable stochastic gravitational wave (GW) signals. These results highlight the complementarity of dark matter searches, muon-collider probes, and SFOEWPT, with the resulting GW signals providing an additional probe of the extended scalar sector.

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arXiv2026

From Thermal History to Multi-Messenger Signatures in $\mathbb{Z}_3$ Symmetric Dark Sector

We investigate a $\mathbb{Z}_3$-symmetric extension of the Standard Model consisting of a right-handed neutrino ($N_R$), a dark fermion ($\chi$) that dominates the relic density and a dark complex scalar ($S$) that facilitates a strong first-order electroweak phase transition (SFOEWPT). The observed relic abundance, is achieved through the combined effects of annihilation, semi-annihilation, and dark-sector conversion processes over a broad region of parameter space consistent with a SFOEWPT. We further investigate the resulting multi-messenger signatures, including loop-induced direct detection, indirect detection through gamma-ray observations, and gravitational wave signals, with the latter lying within the projected sensitivities of future space-based detectors such as LISA, BBO, and DECIGO.

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arXiv2026

A Non-Holomorphic Modular $A_4$ Framework for Resonant Leptogenesis with Gravitational Wave Signatures

We study a type-I seesaw framework based on non-holomorphic $A_4$ modular symmetry, where polyharmonic Maa\ss\ forms construct the Yukawa couplings and right-handed neutrino (RHN) Majorana mass matrix. The use of non-holomorphic modular forms yields highly constrained neutral lepton mass matrices with a more restrictive lepton-sector structure and naturally generates a quasi-degenerate RHN mass spectrum, enabling resonant leptogenesis at an intermediate scale with RHN masses of $\mathcal{O}(10^3)$ TeV without requiring an ad hoc mass degeneracy. We further extend the model by introducing a complex scalar field $(\Phi)$ charged under $\mathbb{Z}_3$ symmetry. The spontaneous breaking of the discrete symmetry after the phase transition associated with $\Phi$ leads to domain-wall (DW) formation. A radiatively induced bias term associated with the RHN sector triggers DW annihilation, resolving the cosmological DW problem, and producing a stochastic gravitational wave (GW) signal that indirectly probes the RHN mass scale. The accompanying first-order phase transition produces a second GW peak, yielding a characteristic double-peaked spectrum with frequencies separated by several orders of magnitude and potentially observable by complementary future GW detectors.

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arXiv2026

Solving Cosmological Puzzles using Finite Temperature $\nu$SMEFT

We study a minimal framework that naturally yields viable Dark Matter, a strong first-order electroweak phase transition and low-scale resonant leptogenesis. Augmenting the Standard Model with three heavy Majorana neutrinos, we study the corresponding neutrino-extended Standard Model Effective Field Theory, including operators upto mass-dimension six. The pure Higgs operator provides the dominant enhancement required for a strong first-order electroweak phase transition, while the remaining operators yield subleading effects consistent with electroweak precision constraints. The signal for the stochastic gravitational-wave background is dominated by sound waves in the plasma, with magnetohydrodynamic turbulence providing a subleading contribution. Low-scale resonant leptogenesis is realized through tiny mass splittings among quasi-degenerate heavy neutrinos, dynamically generated in the symmetric phase by the combined effect of one-loop RG-induced corrections and finite-temperature contributions. Solving the Boltzmann equations, we show that the observed baryon asymmetry of the Universe can be reproduced while remaining consistent with neutrino oscillation data and charged-lepton-flavor-violation constraints. One of the heavy neutrinos is stabilized by a discrete symmetry thereby acting as a fermionic dark matter candidate. Its interactions with the Standard Model arise from dimension-five and dimension-six effective operators, leading to viable annihilation, elastic scattering, and indirect detection phenomenology compatible with current experimental bounds. The dark matter sector remains decoupled from the dynamics of the electroweak phase transition and leptogenesis, allowing all three phenomena to be consistently realized within a unified effective field theory framework.

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arXiv2026

Revisiting Singlet Fermion Dark Matter with a Scalar Portal: Connecting Higgs Phenomenology and Strong Electroweak Phase Transition

We investigate a minimal extension of the Standard Model with a real singlet scalar and a singlet Dirac fermion acting as dark matter. Unlike a conventional singlet scalar setup, we assume that the singlet scalar does not acquire a vacuum expectation value at zero temperature. This decouples the scalar mixing angle from the Higgs-portal quartic coupling responsible for the strong first-order electroweak phase transition, allowing it to coexist with current collider and direct-detection constraints. The Higgs-singlet mixing is generated independently through a trilinear portal interaction. We check theoretical consistency conditions, various LHC limits on heavy scalar resonances, dark matter relic abundance, and direct detection bounds to delineate the viable parameter space. We perform a detailed analysis of the electroweak phase transition and show that a strong first-order transition is realized for a selected set of benchmark points. We further compute the resulting stochastic gravitational wave spectra and find that several scenarios yield signals potentially observable at future space-based interferometers. Our results establish a unified and testable framework that connects collider phenomenology, first-order electroweak phase transition, and the resulting production of gravitational waves, along with the dark matter phenomenology, all within a simple renormalizable extension of the Standard Model.

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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

Two-loop dimension Six Effective Action: Integrating Out Heavy Scalar

For the first time, we present the model-independent two-loop effective action up to dimension six after integrating out heavy scalar(s) employing the Heat-Kernel method. We compute the effective operators that emerge at two-loop for two example models: heavy electroweak complex Triplet and Doublet scalars. We present our results on the SILH basis. We also capture the effect in the fermion sector. For these two scenarios, we compute all the fermionic effective operators up to dimension six.

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arXiv2023

Soft photon corrections in $B \to K^{(\ast)} \ell^+ \ell^-$ and $\Lambda_b \to \Lambda^{(\ast)} \ell^+ \ell^-$ decays

We calculate QED corrections to the semileptonic decays $H_1 \to H_2\ell^+\ell^-$ where $\ell=e, \mu$ and $H_{1,2}$ are hadrons. The soft and/or collinear divergences are regulated in a gauge-invariant manner and demonstrably cancel, leaving behind a finite residue that depends on the (infrared) momentum cutoff below which a photon is considered to be indistinguishable. On resuming, the said sensitivity reduces drastically, $\mathcal{i}$.$\mathcal{e}$., for the NLL result as compared to the NLO one. The overall correction is negative and its magnitude is larger for a lighter lepton. For $B \to K^{(*)}$ decays, the corrections improve the agreement for the differential distributions, while the behavior is more complicated for $\Lambda_b \to \Lambda^{(*)}$ decays. Rather intriguingly, the corrections serve to regenerate the tension for the lepton flavor universality observables $R_K$ and $R_{K^*}$.

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arXiv2023

Veltman Criteria in Beyond Standard Model Effective Field Theory of Complex Scalar Triplet

The Higgs mass is not protected by any symmetry in the Standard Model. Hence, the self-energy corrections to the Higgs mass become large due to the quadratic divergence terms. Veltman condition (V.C.) ensures that the coefficient of the quadratic divergent term either vanishes or becomes negligible. The non-observation of new physics has pushed the new physics scale to be larger than 1 TeV, making it impossible to satisfy the Veltman condition in the Standard Model without very large fine-tuning. Many attempts are made to satisfy the V.C. in Beyond Standard Model theories, but the V.C. is hard to achieve at a very large scale ($\Lambda$). Alternatively, it is possible that the new physics appears much above the Electroweak scale, and the effect of the new physics is observed in terms of the Wilson coefficients of the Standard Model Effective Field Theory (SMEFT) operators. The V.C. can be addressed in the SMEFT framework. In this paper, some specific new physics scenarios are considered at a very large scale. Below that scale, the effect of the new physics is observed as Beyond Standard Model Effective Field Theory (BSM-EFT). We particularly study the type-II seesaw model with the complex scalar triplet ($Y=1$) in the context of V.C. We found that this particular model is the minimal model to generate all SMEFT operators that appear in V.C. and satisfies V.C. We also examine the model parameter dependence of the Wilson coefficients in detail and show how the cancellation of the Wilson coefficients is highly dependent on some specific values of the model parameters.

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arXiv2022

$\Lambda_b\rightarrow \Lambda(\to p \pi^-) \ell^+\ell^-$ as probe of CP-violating New Physics

We investigate the possible sizes of all the CP-violating asymmetries offered by the angular distribution of rare decay $\Lambda_b\rightarrow \Lambda(\to p \pi^-) \ell^+\ell^-$ in the Standard Model and new physics scenarios motivated by the recent $b\to s \ell^+\ell^-$ anomalies. We work in a model-independent effective theory framework and discuss the sensitivity of CP asymmetries to new ${O}_{9,10}$ operators and their chirality flipped counterparts. We find that the size of many of the CP asymmetries can be at the level of a few percent in new physics scenarios consistent with current $b\to s\ell^+\ell^-$ data at a level of $1\sigma$. We emphasize that measurements of these CP asymmetries can be used to discriminate different new physics scenarios in $b\to s \ell^+\ell^-$.

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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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arXiv2021

Sterile neutrinos in $\Lambda_b^0\to (\Lambda_c^+,p^+)\ell^-_1\ell^-_2\ell^+_3\nu$ decays

We study lepton number violating and lepton number conserving semi-leptonic decays of heavy baryons $\Lambda_b^0$ to three charged leptons and a neutrino. The decays occur through two intermediate quasi-degenerate GeV-scale sterile neutrinos of either Majorana or Dirac type that can be on-shell. Interference between the intermediate heavy neutrinos leads to CP violation in the final states. Effect of neutrino oscillations between the heavy states are also considered in observables of interests, \emph{i.e.,} branching ratio, and the CP-asymmetry. Given the present constraints on the heavy-to-light mixing elements $|V_{eN}|$ and $|V_{\mu N}|$, CP-averaged branching ratio of $\Lambda_b^0\to (\Lambda_c,p)\mu\mu e\nu$ with intermediate Majorana neutrinos is almost two orders of magnitude larger than for the same with Dirac neutrinos, whereas, CP-averaged branching ratio of $\Lambda_b^0\to (\Lambda_c,p)ee\mu\nu$ is of the same order of magnitude for both Majorana and Dirac neutrino induced decays. CP-violation is found to be appreciable when the neutrino mass difference is comparable with the average decay widths.

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arXiv2021

CP violation with GeV-scale Majorana neutrino in $Λ_b\to(Λ_c^+, p^+)π^+μ^-μ^-$ decays

We explore the possibility of CP violation in baryonic $Λ_b\to(Λ_c^+, p^+)π^+μ^-μ^-$ decays which are mediated by two Majorana sterile neutrino and are $|ΔL|=2$ lepton number violating processes. Appreciable CP asymmetry can be obtained if there are two on-shell Majorana neutrinos that are quasi-degenerate in mass with the mass difference of the order of average decay widths. We find that given the present constraints on the heavy to light mixing element $|V_{μN}|$, the $Λ_b\to p^+π^+μ^-μ^-$ and $Λ_b\to Λ_c^+π^+μ^-μ^-$ decay rates are suppressed but could be within the experimental reach at the LHC. If searches of the modes are performed, then experimental limits on the rates can be translated to constraints on the Majorana neutrino mass $m_N$ and heavy to light mixing element squared $|V_{μN}|^2$. We show that the constraints on the $(m_N, |V_{μN}|^2)$ parameter space coming from the $|ΔL| = 2$ baryonic decays are complementary to the bounds coming from other processes.

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arXiv2020

The $Λ_b\toΛ^\ast(1520)(\to N\!\bar{K})\ell^+\ell^-$ decay at low-recoil in HQET

In this paper we discuss the Standard Model and new physics sensitivity of the $Λ_b\toΛ^\ast(1520)(\to N\!\bar{K})\ell^+\ell^-$ decay at low-recoil, where $\ell^\pm$ are massive leptons and $N\!\bar{K}=\{pK^-, n\bar{K}^0 \}$. We provide a full angular distribution with a set of operators that includes the Standard Model operators and their chirality flipped counterparts, and new scalar and pseudo-scalar operators. The resulting angular distribution allows us to construct observables that we study in the Standard Model and in model-independent new physics scenarios. To reduce the hadronic effects emanating from the $Λ_b\toΛ^\ast(1520)$ transition form factors, we exploit the Heavy Quark Effective theory framework valid at low $Λ^\ast(1520)$ recoil, \emph{i.e.,} large dilepton invariant mass squared $q^2\sim \mathcal{O}(m_b^2)$. Working to the leading order in $1/m_b$ and including $\mathcal{O}(α_s)$ corrections, we compute the `improved Isgur-Wise relations' between the form factors. The relations correlate the form factors and thereby allow the description of this decay at the low-recoil region with a smaller number of independent form factors.

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