arXiv subjects

Rishav Roshan

Publications and source records attributed to Rishav Roshan.

45 records · Page 3Linked to original sources

arXiv2022

Non-minimally Coupled Vector Boson Dark Matter

We consider a simple abelian vector dark matter (DM) model, where {\it only} the DM $(\widetilde{X}_μ)$ couples non-minimally to the scalar curvature $(\widetilde{R})$ of the background spacetime via an operator of the form $\sim \widetilde{X}_μ\,\widetilde{X}^μ\,\widetilde{R}$. By considering the standard freeze-out scenario, we show, it is possible to probe such a non-minimally coupled DM in direct detection experiments for a coupling strength $ξ\sim\mathcal{O}\left(10^{30}\right)$ and DM mass $m_X\lesssim 55$ TeV, satisfying Planck observed relic abundance and perturbative unitarity. We also discuss DM production via freeze-in, governed by the non-minimal coupling, that requires $ξ\lesssim 10^{-5}$ to produce the observed DM abundance over a large range of DM mass depending on the choice of the reheating temperature. We further show, even in the absence of the non-minimal coupling, it is possible to produce the whole observed DM abundance via 2-to-2 scattering of the bath particles mediated by massless gravitons.

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arXiv2021

Imprint of the seesaw mechanism on feebly interacting dark matter and the baryon asymmetry

We show that the type-I seesaw, responsible for generating the light neutrino mass, itself is capable of accommodating one of the three right handed neutrinos as a freeze-in type of dark matter (DM) where the required smallness of the associated coupling is connected to the lightness of the (smallest) active neutrino mass. It turns out that (a) the non-thermal production of DM having mass $\lesssim \mathcal{O}(1)$ MeV (via decays of $W, Z$ bosons and SM Higgs) consistent with relic density as well as (b) its stability determine this smallest active neutrino mass uniquely $\sim {\mathcal{O}}(10^{-12})$ eV. On the other hand, the study of flavor leptogenesis in this scenario (taking into account the latest neutrino data and Higgs vacuum stability issue) fixes the scale of two other right handed neutrinos.

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arXiv2021

Non-thermal leptogenesis and UV freeze-in of dark matter: impact of inflationary reheating

We study a minimal scenario to realize non-thermal leptogenesis and UV freeze-in of a Standard Model (SM) gauge singlet fermionic dark matter (DM) simultaneously, with inflaton field playing a non-trivial role in their yields. The renormalizable interactions are restricted to the SM fields, two right handed neutrinos (RHN) and inflaton coupling exclusively to the RHNs, while the DM couples to both the SM and the RHNs only via operators of dimension $d>4$. Considering two separate cases of $d=\{5,6\}$, we show that for $d=5$, inflaton decay into RHNs followed by their subsequent decay into SM particles lead to both reheating as well as DM production from the SM bath. This requires a cut-off scale as large as $Λ\sim 10^{17}~\rm GeV$ depending on the DM mass. On the other hand, for $d=6$, DM production happens directly from scattering of RHNs (for $Λ\gtrsim 10^{14}~\rm GeV$) that results in a very non-trivial evolution of the DM yield. In both these cases, it is possible to explain the observed baryon asymmetry through successful non-thermal leptogenesis via the decay of the RHNs, together with the PLANCK observed relic density of the DM via pure UV freeze-in mechanism. Taking into account both instantaneous as well as non-instantaneous reheating separately, we constrain the parameter space of this minimal scenario from relevant phenomenological requirements including sub-eV scale active neutrino masses and their mixing.

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arXiv2021

Two Component Singlet-Triplet Scalar Dark Matter and Electroweak Vacuum Stability

We propose a two component dark matter set-up by extending the Standard Model with a singlet and a hypercharge-less triplet scalars, each of them being odd under different $Z_2$ symmetries. We observe that the inter-conversion between the two dark matter components allow a viable parameter space where masses of both the dark matter candidates can be below TeV, even though their individual contribution to single component dark matter rules out any such sub-TeV dark matter. We find that a lighter mass of the neutral component of the scalar triplet, playing the role of one dark matter component, compared to the scalar one is favored. In addition, the set-up is shown to make the electroweak vacuum absolutely stable till the Planck scale, thanks to Higgs portal coupling with the scalar dark matter components.

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arXiv2021

Neutrino mass and asymmetric dark matter: study with inert Higgs doublet and high scale validity

We consider an inert Higgs doublet (IHD) extension of the Standard Model accompanied with three right handed neutrinos and a dark sector, consisting of a singlet fermion and a scalar, in order to provide a common framework for dark matter, leptognesis and neutrino mass. While the Yukawa coupling of the right handed neutrinos with IHD (having mass in the intermediate regime: 80-500 GeV) is responsible for explaining the observed baryon asymmetry through leptogenesis, its coupling with the dark sector explains the dark matter relic density. The presence of IHD also explains the neutrino mass through radiative correction. We find that study of the high scale validity of the model in this context becomes crucial as it restricts the parameter space significantly. It turns out that there exists a small, but non-zero contribution to the relic density of DM from IHD too. Considering all the constraints from dark matter, leptogenesis, neutrino mass and high scale validity of the model, we perform a study to find out the viable parameter space.

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arXiv2020

Sub-TeV Singlet Scalar Dark Matter and Electroweak Vacuum Stability with Vector Like Fermions

We study a scalar singlet dark matter (DM) having mass in sub-TeV regime by extending the minimal scalar singlet DM setup by additional vector like fermions. While the minimal scalar singlet DM satisfies the relic and direct detection constraints for mass beyond TeV only, presence of its portal coupling with vector like fermions opens up additional co-annihilation channels. These vector like fermions also help in achieving electroweak vacuum stability all the way up to Planck scale. We find that for one generation of vector like quarks consisting of a $SU(2)_L$ doublet and a singlet, scalar singlet DM with mass a few hundred GeV can indeed satisfy relic, direct detection and other relevant constraints while also making the electroweak vacuum absolutely stable. The same can be achieved by introducing vector like leptons too, but with three generations. While the model with vector like quarks is minimal, the three generations of vector like lepton doublet and neutral singlet can also give rise to light neutrino mass at one loop level.

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arXiv2020

Effective Theory of Freeze-in Dark Matter

We perform a model independent study of freeze-in of massive particle dark matter (DM) by adopting an effective field theory framework. Considering the dark matter to be a gauge singlet Majorana fermion, odd under a stabilising symmetry $Z_2$ under which all standard model (SM) fields are even, we write down all possible DM-SM operators upto and including mass dimension eight. For simplicity of the numerical analysis we restrict ourselves only to the scalar operators in SM as well as in the dark sector. We calculate the DM abundance for each such dimension of operator considering both UV and IR freeze-in contributions which can arise before and after the electroweak symmetry breaking respectively. After constraining the cut-off scale and reheat temperature of the universe from the requirement of correct DM relic abundance, we also study the possibility of connecting the origin of neutrino mass to the same cut-off scale by virtue of lepton number violating Weinberg operators. We thus compare the bounds on such cut-off scale and corresponding reheat temperature required for UV freeze-in from the origin of light neutrino mass as well as from the requirement of correct DM relic abundance. We also briefly comment upon the possibilities of realising such DM-SM effective operators in a UV complete model.

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arXiv2020

Multicomponent dark matter in extended $U(1)_{B-L}$: neutrino mass and high scale validity

Standard Model with right handed neutrinos charged under additional $U(1)_{B-L}$ gauge symmetry offer solutions to both dark matter (DM) problem and neutrino mass generation, although constrained severely from relic density, direct search and Higgs vacuum stability. We therefore investigate a multicomponent DM scenario augmented by an extra inert scalar doublet, that is neutral under $U(1)_{B-L}$, which aids to enlarge parameter space allowed by DM constraints and Higgs vacuum stability. The lightest right-handed neutrino and the $CP$-even inert scalar are taken as the dark matter candidates and constitute a two component dark matter framework as they are rendered stable by an unbroken $\mathbb{Z}_2 \times \mathbb{Z}_2^\prime$ symmetry. DM-DM conversion processes turn out crucial to render requisite relic abundance in mass regions of the RH neutrino that do not appear in the stand-alone $U(1)_{B-L}$ scenario. In addition, the one-loop renormalisation group (RG) equations in this model demonstrate that the electroweak (EW) vacuum can be stabilised till $\sim 10^{9}$ GeV in a parameter region compatible with the observed relic, the direct detection bound and other relevant constraints.

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arXiv2019

Minimal Two-component Scalar Doublet Dark Matter with Radiative Neutrino Mass

We propose a minimal extension of the Standard Model to accommodate two-component dark matter (DM) and light neutrino mass. The symmetry of the Standard Model is enhanced by an unbroken $\mathbb{Z}_2 \times \mathbb{Z}'_2$ such that being odd under each $\mathbb{Z}_2$, there exists one right handed neutrino and one inert scalar doublet. Therefore, each of the $\mathbb{Z}_2$ sectors contribute to ($i$) light neutrino masses radiatively similar to the scotogenic models while ($ii$) the two neutral CP even scalars present in two additional inert doublets play the role of dark matters. Focusing on the intermediate range of inert scalar doublet DM scenario: $M_W \leq M_{\rm DM} \lesssim 500 \; {\rm GeV}$, where one scalar doublet DM can not satisfy correct relic, we show that this entire range becomes allowed within this two-component scalar doublet DM, thanks to the inter-conversion between the two DM candidates in presence of neutrino Yukawa couplings with dark sector.

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