arXiv subjects

Dibyendu Nanda

Publications and source records attributed to Dibyendu Nanda.

31 records · Page 2Linked to original sources

arXiv2022

Anomalous Magnetic Moment and Higgs Coupling of the Muon in a Sequential U(1) Gauge Model with Dark Matter

We study an Abelian gauge extension of the standard model with fermion families having non-universal gauge charges. The gauge charges and scalar content are chosen in such an anomaly-free way that only the third generation fermions receive Dirac masses via renormalisable couplings with the Higgs boson. Incorporating additional vector like fermions and scalars with appropriate $U(1)$ charges can lead to radiative Dirac masses of first two generations with neutral fermions going in the loop being dark matter candidates. Focusing on radiative muon mass, we constrain the model from the requirement of satisfying muon mass, recently measured muon anomalous magnetic moment by the E989 experiment at Fermilab along with other experimental bounds including the large hadron collider (LHC) limits. The anomalous Higgs coupling to muon is constrained from the LHC measurements of Higgs to dimuon decay. The singlet fermion dark matter phenomenology is discussed showing the importance of both annihilation and coannihilation effects. Incorporating all bounds lead to a constrained parameter space which can be probed at different experiments.

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arXiv2021

Light Dirac neutrino portal dark matter with observable $Δ{N_{\rm eff}}$

We propose a Dirac neutrino portal dark matter scenario by minimally extending the particle content of the Standard Model (SM) with three right handed neutrinos ($ν_R$), a Dirac fermion dark matter candidate ($ψ$) and a complex scalar ($ϕ$), all of which are singlets under the SM gauge group. An additional $\mathbb{Z}_4$ symmetry has been introduced for the stability of dark matter candidate $ψ$ and also ensuring the Dirac nature of light neutrinos at the same time. Both the right handed neutrinos and the dark matter thermalise with the SM plasma due to a new Yukawa interaction involving $ν_R$, $ψ$ and $ϕ$ while the latter maintains thermal contact via the Higgs portal interaction. The decoupling of $ν_R$ occurs when $ϕ$ loses its kinetic equilibrium with the SM plasma and thereafter all three $\mathbb{Z}_4$ charged particles form an equilibrium among themselves with a temperature $T_{ν_R}$. The dark matter candidate $ψ$ finally freezes out within the dark sector and preserves its relic abundance. We have found that in the present scenario, some portion of low mass dark matter ($M_ψ\lesssim10$ GeV) is already excluded by the Planck 2018 data for keeping $ν_R$s in the thermal bath below a temperature of 600 MeV and thereby producing an excess contribution to $N_{\rm eff}$. The next generation experiments like CMB-S4, SPT-3G etc. will have the required sensitivities to probe the entire model parameter space of this minimal scenario, especially the low mass range of $ψ$ where direct detection experiments are still not capable enough for detection.

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arXiv2020

Inelastic Fermion Dark Matter Origin of XENON1T Excess with Muon $(g-2)$ and Light Neutrino Mass

Motivated by the recently reported excess in electron recoil events by the XENON1T collaboration, we propose an inelastic fermion dark matter (DM) scenario within the framework of a gauged $L_μ-L_τ$ extension of the standard model which can also accommodate tiny neutrino masses as well as anomalous muon magnetic moment $(g-2)_μ$. A Dirac fermion DM, naturally stabilised due to its chosen gauge charge, is split into two pseudo-Dirac mass eigenstates due to Majorana mass term induced by singlet scalar which also takes part in generating right handed neutrino masses responsible for type I seesaw origin of light neutrino masses. The inelastic down scattering of heavier DM component can give rise to the XENON1T excess for keV scale mass splitting with lighter DM component. We fit our model with XENON1T data and also find the final parameter space by using bounds from $(g-2)_μ$, DM relic, lifetime of heavier DM, inelastic DM-electron scattering rate, neutrino trident production rate as well as other flavour physics, astrophysical and cosmological observations. A tiny parameter space consistent with all these bounds and requirements will face further scrutiny in near future experiments operating at different frontiers.

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arXiv2020

Observing Left-Right Symmetry in the Cosmic Microwave Background

We consider the possibility of probing left-right symmetric model (LRSM) via cosmic microwave background (CMB). We adopt the minimal LRSM with Higgs doublets, also known as the doublet left-right model (DLRM), where all fermions including the neutrinos acquire masses only via their couplings to the Higgs bidoublet. Due to the Dirac nature of light neutrinos, there exist additional relativistic degrees of freedom which can thermalise in the early universe by virtue of their gauge interactions corresponding to the right sector. We constrain the model from Planck 2018 bound on the effective relativistic degrees of freedom and also estimate the prospects for planned CMB Stage IV experiments to constrain the model further. We find that $W_R$ boson mass below 4.06 TeV can be ruled out from Planck 2018 bound at $2σ$ CL in the exact left-right symmetric limit which is equally competitive as the LHC bounds from dijet resonance searches. On the other hand Planck 2018 bound at $1σ$ CL can rule out a much larger parameter space out of reach of present direct search experiments, even in the presence of additional relativistic degrees of freedom around the TeV corner. We also study the consequence of these constraints on dark matter in DLRM by considering a right handed real fermion quintuplet to be the dominant dark matter component in the universe.

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arXiv2020

Connecting Light Dirac Neutrinos to a Multi-component Dark Matter Scenario in Gauged $B-L$ Model

We propose a new gauged $B-L$ extension of the standard model where light neutrinos are of Dirac type, naturally acquiring sub-eV mass after electroweak symmetry breaking, without any additional global symmetries. This is realised by choosing a different $B-L$ charge for right handed neutrinos than the usual $-1$ so that the Dirac Yukawa coupling involves an additional neutrinophilic scalar doublet instead of the usual Higgs doublet. The model can be made anomaly free by considering four additional chiral fermions which give rise to two massive Dirac fermions by appropriate choice of singlet scalars. The choice of scalars not only helps in achieving the desired particle mass spectra via spontaneous symmetry breaking, but also leaves a remnant $Z_2 \times Z'_2$ symmetry to stabilise the two dark matter candidates. Apart from this interesting link between Dirac nature of light neutrinos and multi-component dark matter sector, we also find that the dark matter parameter space is constrained mostly by the cosmological upper limit on effective relativistic degrees of freedom $ΔN_{\rm eff}$ which gets enhanced in this model due to the thermalisation of the light right handed neutrinos by virtue of their sizeable $B-L$ gauge interactions.

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arXiv2020

Common origin of modified chaotic inflation, non thermal dark matter and Dirac neutrino mass

We propose a minimal extension of the standard model of particle physics to accommodate cosmic inflation, dark matter and light neutrino masses. While the inflationary phase is obtained from a modified chaotic inflation scenario, consistent with latest cosmology data, the dark matter particle is a fermion singlet which remains out of equilibrium in the early universe. The scalar field which revives the chaotic inflation scenario by suitable modification also assists in generating tiny couplings of dark matter with its mother particle, naturally realizing the non-thermal or freeze-in type dark matter scenario. Interestingly, the same assisting scalar field also helps in realizing tiny Yukawa couplings required to generate sub-eV Dirac neutrino mass from neutrino couplings to the standard model like Higgs field. The minimality as well as providing a unified solution to all three problems keep the model predictive at experiments spanning out to all frontiers.

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arXiv2019

Type III Seesaw for Neutrino Masses in $U(1)_{B-L}$ Model with Multi-component Dark Matter

We propose a $B-L$ gauged extension of the Standard Model where light neutrino masses arise from type III seesaw mechanism. Unlike the minimal $B-L$ model with three right handed neutrinos having unit lepton number each, the model with three fermion triplets is however not anomaly free. We show that the leftover triangle anomalies can be cancelled by two neutral Dirac fermions having fractional $B-L$ charges, both of which are naturally stable by virtue of a remnant $\mathbb{Z}_2 \times \mathbb{Z}'_2$ symmetry, naturally leading to a two component dark matter scenario without any ad-hoc symmetries. We constrain the model from all relevant phenomenological constraints including dark matter properties. Light neutrino mass and collider prospects are also discussed briefly. Due to additional neutral gauge bosons, the fermion triplets in type III seesaw can have enhanced production cross section in collider experiment.

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arXiv2019

Right-handed Neutrino Dark Matter with Radiative Neutrino Mass in Gauged $B-L$ Model

We study the possibility of right-handed neutrino dark matter (DM) in gauged $U(1)_{B-L} \times Z_2$ extension of the standard model augmented by an additional scalar doublet, being odd under the $Z_2$ symmetry, to give rise the scotogenic scenario of radiative neutrino masses. Due to lepton portal interactions, the right-handed neutrino DM can have additional co-annihilation channels apart from the usual annihilations through $Z_{B-L}$ which give rise to much more allowed mass of DM from relic abundance criteria, even away from the resonance region like $M_{\rm DM} \approx M_{Z_{B-L}}/2$. This enlarged parameter space is found to be consistent with neutrino mass constraints while being sensitive to direct detection experiments of DM as well as rare decay experiments looking for charged lepton flavour violating decays like $μ\rightarrow e γ$. Due to the possibility of the $Z_2$ odd scalar doublet being the next to lightest stable particle that can be sufficiently produced in colliders by virtue of its gauge interactions, one can have interesting signatures like displaced vertex or disappearing charged tracks provided that the mass splitting $δM$ between DM and the next to lightest stable particle (NLSP) is small. In particular, if $δM < m_τ=1.77$ GeV, then we get large displaced vertex signature of NLSP while being consistent with neutrino mass, lepton flavour violation and observed relic density.

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arXiv2019

Planck Scale Origin of Non-zero $θ_{13}$ and Super-WIMP Dark Matter

We study a discrete flavour symmetric scenario for neutrino mass and dark matter under the circumstances where such global discrete symmetries can be explicitly broken at Planck scale, possibly by gravitational effects. Such explicit breaking of discrete symmetries mimic as Planck suppressed operators in the model which can have non-trivial consequences for neutrino and dark matter sectors. In particular, we study a flavour symmetric model which, at renormalisable level, gives rise to tri-bimaximal type neutrino mixing with vanishing reactor mixing angle $θ_{13}=0$, a stable inert scalar doublet behaving like a weakly interacting massive particle (WIMP) and a stable singlet inert fermion which does not interact with any other particles. The introduction of Planck suppressed operators which explicitly break the discrete symmetries, can give rise to the generation of non-zero $θ_{13}$ in agreement with neutrino data and also open up decay channels of inert scalar doublet into singlet neutral inert fermion leading to the realisation of the super-WIMP dark matter scenario. We show that the correct neutrino phenomenology can be obtained in this model while discussing three distinct realisation of the super-WIMP dark matter scenario.

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arXiv2018

keV Neutrino Dark Matter in a Fast Expanding Universe

We study the possibility of keV neutrino dark matter in the minimal $U(1)_{B-L}$ gauge extension of the standard model where three right handed neutrinos are automatically included due to the requirement of anomaly cancellations. Without considering extra additional particles or symmetries, we consider the lightest right handed neutrino to be in the keV mass range which is kinematically long lived. Due to gauge interactions, such a keV neutrino can be thermally produced in the early Universe followed by decoupling while being relativistic. The final relic abundance of such keV neutrino typically overclose the Universe requiring additional mechanism to bring it under observed limits. We propose a non-standard cosmological history where a scalar field $ϕ$, that redshifts faster than radiation dominates the Universe prior to the radiation dominated era. We show that such a non-standard phase can keep the abundance of thermally generated keV neutrino dark matter within observed relic abundance. We constrain the non-standard phase, $U(1)_{B-L}$ parameters from these requirements and also briefly comment upon the observational aspects of such keV neutrino dark matter.

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arXiv2018

When Freeze-out Precedes Freeze-in: Sub-TeV Fermion Triplet Dark Matter with Radiative Neutrino Mass

We propose a minimal predictive scenario for dark matter and radiative neutrino mass where the relic abundance of dark matter is generated from a hybrid setup comprising of both thermal freeze-out as well as non-thermal freeze-in mechanisms. Considering three copies of fermion triplets and one scalar doublet, odd under an unbroken $\mathbb{Z}_2$ symmetry, to be responsible for radiative origin of neutrino mass, we consider the lightest fermion triplet as a dark matter candidate which remains under-abundant in the sub-TeV regime from usual thermal freeze-out. Late decay of the $\mathbb{Z}_2$-odd scalar doublet into dark matter serves as the non-thermal (freeze-in) contribution which not only fills the thermal dark matter deficit, but also constrains the mother particle's parameter space so that the correct relic abundance of dark matter is generated. Apart from showing interesting differences from the purely freeze-out and purely freeze-in dark matter scenarios, the model remains testable through disappearing charge track signatures at colliders, observable direct and indirect detection rates for dark matter and prediction of almost vanishing lightest neutrino mass.

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arXiv2018

Common Origin of Dirac Neutrino Mass and Freeze-in Massive Particle Dark Matter

Motivated by the fact that the origin of tiny Dirac neutrino masses via the standard model Higgs field and non-thermal dark matter populating the Universe via freeze-in mechanism require tiny dimensionless couplings of similar order of magnitudes $(\sim 10^{-12})$, we propose a framework that can dynamically generate such couplings in a unified manner. Adopting a flavour symmetric approach based on $A_4$ group, we construct a model where Dirac neutrino coupling to the standard model Higgs and dark matter coupling to its mother particle occur at dimension six level involving the same flavon fields, thereby generating the effective Yukawa coupling of same order of magnitudes. The mother particle for dark matter, a complex scalar singlet, gets thermally produced in the early Universe through Higgs portal couplings followed by its thermal freeze-out and then decay into the dark matter candidates giving rise to the freeze-in dark matter scenario. Some parts of the Higgs portal couplings of the mother particle can also be excluded by collider constraints on invisible decay rate of the standard model like Higgs boson. We show that the correct neutrino oscillation data can be successfully produced in the model which predicts normal hierarchical neutrino mass. The model also predicts the atmospheric angle to be in the lower octant if the Dirac CP phase lies close to the presently preferred maximal value.

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arXiv2017

Common Origin of Neutrino Mass and Dark Matter from Anomaly Cancellation Requirements of a $U(1)_{B-L}$ Model

We study a gauged $B-L$ extension of the standard model where the new fermions with fractional $B-L$ charges that play the role of keeping the model anomaly free can also explain the origin of neutrino mass at one loop level as well as dark matter. We discuss two different versions of the model to realise fermion and scalar dark matter, both of which guarantee the dark matter stability by a remnant discrete symmetry to which $U(1)_{B-L}$ gauge symmetry gets spontaneously broken down to. Apart from giving rise to the observed neutrino mass and dark matter abundance, the model also has tantalising signatures at variety of experiments operating at cosmic, intensity and energy frontiers, particularly direct and indirect detection experiments of dark matter, rare decay experiments looking for charged lepton flavour violation as well as collider experiments. The model also predicts vanishing lightest neutrino mass that can be tested at experiments sensitive to the absolute neutrino mass scale.

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