arXiv subjects

Anirban Biswas

Publications and source records attributed to Anirban Biswas.

At least 37 records · Page 2Linked to original sources

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

Explaining Dark Matter and Neutrino Mass in the light of TYPE-II Seesaw Model

With the motivation of simultaneously explaining dark matter and neutrino masses, mixing angles, we have invoked the Type-II seesaw model extended by an extra $SU(2)$ doublet $Φ$. Moreover, we have imposed a $\mathbb{Z}_2$ parity on $Φ$ which remains unbroken as the vacuum expectation value of $Φ$ is zero. Consequently, the lightest neutral component of $Φ$ becomes naturally stable and can be a viable dark matter candidate. On the other hand, light Majorana masses for neutrinos have been generated following usual Type-II seesaw mechanism. Further in this framework, for the first time, we have derived the full set of vacuum stability and unitarity conditions, which must be satisfied to obtain a stable vacuum as well as to preserve the unitarity of the model respectively. Thereafter, we have performed extensive phenomenological studies of both dark matter and neutrino sectors considering all possible theoretical and current experimental constraints. Finally, we have also discussed a qualitative collider signatures of dark matter and associated odd particles at the 13 TeV Large Hadron Collider.

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arXiv2019

Common origin of baryon asymmetry, dark matter and neutrino mass

In this work, we explain three beyond standard model (BSM) phenomena, namely neutrino masses, the baryon asymmetry of the Universe and Dark Matter, within a single model and in each explanation the right handed (RH) neutrinos play the prime role. Indeed by just introducing two RH neutrinos we can generate the neutrino masses by the Type-I seesaw mechanism. The baryon asymmetry of the Universe can arise from thermal leptogenesis from the decay of lightest RH neutrino before the decoupling of the electroweak sphaleron transitions, which redistribute the $ B-L $ number into a baryon number. At the same time, the decay of the RH neutrino can produce the Dark Matter (DM) as an asymmetric Dark Matter component. The source of CP violation in the two sectors is exactly the same, related to the complex couplings of the neutrinos. By determining the comoving number density for different values of the CP violation in the DM sector, we obtain a particular value of the DM mass after satisfying the relic density bound. We also give prediction for the DM direct detection (DD) in the near future by different ongoing DD experiments.

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arXiv2019

Reconciling dark matter, $R_{K^{(*)}}$ anomalies and $(g-2)_μ$ in an ${L_μ-L_τ}$ scenario

We propose an anomaly free unified scenario by invocation of an extra local ${\rm U(1)}_{L_μ-L_τ}$ gauge symmetry. This scenario simultaneously resolves the $R_{K^{(*)}}$ anomalies, the dark matter puzzle and the long-standing discrepancy in muon's anomalous magnetic moment. A complex scalar ($η$) having nonzero ${L_μ-L_τ}$ charge has been introduced to break this new U(1) symmetry spontaneously. Moreover, for the purpose of studying dark matter phenomenology and $R_{K^{(*)}}$ anomalies in a correlated manner, we introduce an inert ${\rm SU(2)}_L$ scalar doublet ($Φ$), a $\mathbb{Z}_2$-odd real singlet scalar ($S$) and a $\mathbb{Z}_2$-odd coloured fermion ($χ$) which transforms vectorially under the ${\rm U(1)}_{L_μ-L_τ}$ symmetry. This extra gauge symmetry provides a new gauge boson $Z_{μτ}$ which not only gives additional contribution to both $b\to s \ell\ell$ transition and $(g-2)_μ$ but also provides a crucial annihilation channel for dark matter candidate $ρ_1$ of the present scenario. This $ρ_1$ is an admixture of CP-even neutral component of $Φ$ and $S$. Our analysis shows that the low mass dark matter regime ($M_{ρ_1}\lesssim 60$ GeV) is still allowed by the experiments like XENON1T, LHC (via Higgs invisible branching) and Fermi-LAT, making the dark matter phenomenology drastically different from the standard Inert Doublet and the Scalar Singlet models. Furthermore, the present model is also fairly consistent with the observed branching ratio of $B\to X_sγ$ in $3σ$ range and is quite capable of explaining neutrino masses and mixings via Type-I seesaw mechanism if we add three right handed neutrinos in the particle spectrum. Finally, we use the latest ATLAS data of non-observation of a resonant $\ell^+\ell^-$ signal at the 13 TeV LHC to constrain the mass-coupling plane of $Z_{μτ}$.

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arXiv2019

A UV Complete Framework of Freeze-in Massive Particle Dark Matter

We propose a way to generate tiny couplings of freeze-in massive particle dark matter with the Standard Model particles dynamically by considering an extension of the electroweak gauge symmetry. The dark matter is considered to be a singlet under this extended gauge symmetry which we have assumed to be the one in a very widely studied scenario called left-right symmetric model. Several heavy particles, that can be thermally inaccessible in the early Universe due to their masses being greater than the reheat temperature after inflation, can play the role of portals between dark matter and Standard Model particles through one loop couplings. Due to the loop suppression, one can generate the required non-thermal dark matter couplings without any need of highly fine tuned Yukawa couplings beyond that of electron Yukawa with the Standard Model like Higgs boson. We show that generic values of Yukawa couplings as large as $\mathcal{O}(0.01)$ to $\mathcal{O}(1)$ can keep the dark matter out of thermal equilibrium in the early Universe and produce the correct relic abundance later through the freeze-in mechanism. Though the radiative couplings of dark matter are tiny as required by the freeze-in scenario, the associated rich particle sector of the model can be probed at ongoing and near future experiments. The allowed values of dark matter mass can remain in a wide range from keV to TeV order keeping the possibilities of warm and cold dark matter equally possible.

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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

Inverse seesaw and dark matter in a gauged ${\rm B-L}$ extension with flavour symmetry

We propose a model which generates neutrino masses by the inverse seesaw mechanism, provides a viable dark matter candidate and explains the muon ($g-2$) anomaly. The Standard Model (SM) gauge group is extended with a gauged U(1)$_{\rm B-L}$ as well as a gauged U(1)$_{\rm L_μ - L_τ}$. While U(1)$_{\rm L_μ - L_τ}$ is anomaly free, the anomaly introduced by U(1)$_{\rm B-L}$ is cancelled between the six SM singlet fermions introduced for the inverse seesaw mechanism and four additional chiral fermions introduced in this model. After spontaneous symmetry breaking the four chiral fermionic degrees of freedom combine to give two Dirac states. The lightest Dirac fermion becomes stable and hence the dark matter candidate. We focus on the region of the parameter space where the dark matter annihilates to the right-handed neutrinos, relating the dark matter sector with the neutrino sector. The U(1)$_{\rm L_μ - L_τ}$ gauge symmetry provides a flavour structure to the inverse seesaw framework, successfully explaining the observed neutrino masses and mixings. We study the model parameters in the light of neutrino oscillation data and find correlation between them. Values of some of the model parameters are shown to be mutually exclusive between normal and inverted ordering of the neutrino mass eigenstates. Moreover, the muon ($g-2$) anomaly can be explained by the additional contribution arising from U(1)$_{\rm L_μ - L_τ}$ gauge boson.

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arXiv2018

SaC2Vec: Information Network Representation with Structure and Content

Network representation learning (also known as information network embedding) has been the central piece of research in social and information network analysis for the last couple of years. An information network can be viewed as a linked structure of a set of entities. A set of linked web pages and documents, a set of users in a social network are common examples of information network. Network embedding learns low dimensional representations of the nodes, which can further be used for downstream network mining applications such as community detection or node clustering. Information network representation techniques traditionally use only the link structure of the network. But in real world networks, nodes come with additional content such as textual descriptions or associated images. This content is semantically correlated with the network structure and hence using the content along with the topological structure of the network can facilitate the overall network representation. In this paper, we propose Sac2Vec, a network representation technique that exploits both the structure and content. We convert the network into a multi-layered graph and use random walk and language modeling technique to generate the embedding of the nodes. Our approach is simple and computationally fast, yet able to use the content as a complement to structure and vice-versa. We also generalize the approach for networks having multiple types of content in each node. Experimental evaluations on four real world publicly available datasets show the merit of our approach compared to state-of-the-art algorithms in the domain.

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arXiv2018

Explaining the 3.5 keV X-ray Line in a ${L_μ-L_τ}$ Extension of the Inert Doublet Model

We explain the existence of neutrino masses and their flavor structure, dark matter relic abundance and the observed 3.5 keV X-ray line within the framework of a gauged $U(1)_{L_μ - L_τ}$ extension of the "scotogenic" model. In the $U(1)_{L_μ - L_τ}$ symmetric limit, two of the the RH neutrinos are degenerate in mass, while the third is heavier. The $U(1)_{L_μ - L_τ}$ symmetry is broken spontaneously. Firstly, this breaks the $μ-τ$ symmetry in the light neutrino sector. Secondly, this results in mild splitting of the two degenerate RH neutrinos, with their mass difference given in terms of the $U(1)_{L_μ - L_τ}$ breaking parameter. Finally, we get a massive $Z_{μτ}$ gauge boson. Due to the added $Z_2$ symmetry under which the RH neutrinos and the inert doublet are odd, the canonical Type-I seesaw is forbidden and the tiny neutrino masses are generated radiatively at one loop. The same $Z_2$ symmetry also ensures that the lightest RH neutrino is stable and the other two can only decay into the lightest one. This makes the two nearly-degenerate lighter neutrinos a two-component dark matter, which in our model are produced by the freeze-in mechanism via the decay of the $Z_{μτ}$ gauge boson in the early universe. We show that the next-to-lightest RH neutrino has a very long lifetime and decays into the lightest one at the present epoch explaining the observed 3.5 keV line.

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arXiv2017

Neutrino Mass, Leptogenesis and FIMP Dark Matter in a ${\rm U}(1)_{\rm B-L}$ Model

The Standard Model (SM) is inadequate to explain the origin of tiny neutrino masses, the dark matter (DM) relic abundance and also the baryon asymmetry of the Universe. In this work to address all the three puzzles, we extend the SM by a local U$(1)_{\rm B-L}$ gauge symmetry, three right-handed (RH) neutrinos for the cancellation of gauge anomalies and two complex scalars having nonzero U$(1)_{\rm B-L}$ charges. All the newly added particles become massive after the breaking of U$(1)_{\rm B-L}$ symmetry by the vacuum expectation value (VEV) of one of the scalar fields $ϕ_H$. The other scalar field $ϕ_{DM}$, which does not have any VEV, becomes automatically stable and can be a viable DM candidate. Neutrino masses are generated using Type-I seesaw mechanism while the required lepton asymmetry to reproduce the observed baryon asymmetry, can be attained from the CP violating out of equilibrium decays of RH neutrinos in TeV scale. More importantly within this framework, we have studied in detail the production of DM via freeze-in mechanism considering all possible annihilation and decay processes. Finally, we find a situation when DM is dominantly produced from the annihilation of RH neutrinos, which are at the same time also responsible for neutrino mass generation and leptogenesis.

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arXiv2017

Calculation of Momentum Distribution Function of a Non-thermal Fermionic Dark Matter

The most widely studied scenario in dark matter phenomenology is the thermal WIMP scenario. Inspite of numerous efforts to detect WIMP, till now we have no direct evidence for it. A possible explanation for this non-observation of dark matter could be because of its very feeble interaction strength and hence, failing to thermalise with the rest of the cosmic soup. In other words, the dark matter might be of non-thermal origin where the relic density is obtained by the so-called freeze-in mechanism. Furthermore, if this non-thermal dark matter is itself produced substantially from the decay of another non-thermal mother particle, then their distribution functions may differ in both size and shape from the usual equilibrium distribution function. In this work, we have studied such a non-thermal (fermionic) dark matter scenario in the light of a new type of $U(1)_{\rm B-L}$ model. The $U(1)_{\rm B-L}$ model is interesting, since, besides being anomaly free, it can give rise to neutrino mass by Type II see-saw mechanism. Moreover, as we will show, it can accommodate a non-thermal fermionic dark matter as well. Starting from the collision terms, we have calculated the momentum distribution function for the dark matter by solving a coupled system of Boltzmann equations. We then used it to calculate the final relic abundance, as well as other relevant physical quantities. We have also compared our result with that obtained from solving the usual Boltzmann (or rate) equations directly in terms of comoving number density, $Y$. Our findings suggest that the latter approximation is valid only in cases where the system under study is close to equilibrium, and hence should be used with caution.

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arXiv2017

FIMP and Muon ($g-2$) in a U$(1)_{L_μ-L_τ}$ Model

The tightening of the constraints on the standard thermal WIMP scenario has forced physicists to propose alternative dark matter (DM) models. One of the most popular alternate explanations of the origin of DM is the non-thermal production of DM via freeze-in. In this scenario the DM never attains thermal equilibrium with the thermal soup because of its feeble coupling strength ($\sim 10^{-12}$) with the other particles in the thermal bath and is generally called the Feebly Interacting Massive Particle (FIMP). In this work, we present a gauged U(1)$_{L_μ-L_τ}$ extension of the Standard Model (SM) which has a scalar FIMP DM candidate and can consistently explain the DM relic density bound. In addition, the spontaneous breaking of the U(1)$_{L_μ-L_τ}$ gauge symmetry gives an extra massive neutral gauge boson $Z_{μτ}$ which can explain the muon ($g-2$) data through its additional one-loop contribution to the process. Lastly, presence of three right-handed neutrinos enable the model to successfully explain the small neutrino masses via the Type-I seesaw mechanism. The presence of the spontaneously broken U(1)$_{L_μ-L_τ}$ gives a particular structure to the light neutrino mass matrix which can explain the peculiar mixing pattern of the light neutrinos.

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arXiv2016

Two component WIMP-FImP dark matter model with singlet fermion, scalar and pseudo scalar

We explore a two component dark matter model with a fermion and a scalar. In this scenario the Standard Model (SM) is extended by a fermion, a scalar and an additional pseudo scalar. The fermionic component is assumed to have a global ${\rm U(1)}_{\rm DM}$ and interacts with the pseudo scalar via Yukawa interaction while a $\mathbb{Z}_2$ symmetry is imposed on the other component -- the scalar. These ensure the stability of both the dark matter components. Although the Lagrangian of the present model is CP conserving, however the CP symmetry breaks spontaneously when the pseudo scalar acquires a vacuum expectation value (VEV). The scalar component of the dark matter in the present model also develops a VEV on spontaneous breaking of the $\mathbb{Z}_2$ symmetry. Thus the various interactions of the dark sector and the SM sector are progressed through the mixing of the SM like Higgs boson, the pseudo scalar Higgs like boson and the singlet scalar boson. We show that the observed gamma ray excess from the Galactic Centre, self-interaction of dark matter from colliding clusters as well as the 3.55 keV X-ray line from Perseus, Andromeda etc. can be simultaneously explained in the present two component dark matter model.

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arXiv2016

Neutrino Mass, Dark Matter and Anomalous Magnetic Moment of Muon in a $U(1)_{L_μ-L_τ}$ Model

The observation of neutrino masses, mixing and the existence of dark matter are amongst the most important signatures of physics beyond the Standard Model (SM). In this paper, we propose to extend the SM by a local $L_μ- L_τ$ gauge symmetry, two additional complex scalars and three right-handed neutrinos. The $L_μ- L_τ$ gauge symmetry is broken spontaneously when one of the scalars acquires a vacuum expectation value. The $L_μ- L_τ$ gauge symmetry is known to be anomaly free and can explain the beyond SM measurement of the anomalous muon $({\rm g-2})$ through additional contribution arising from the extra $Z_{μτ}$ mediated diagram. Small neutrino masses are explained naturally through the Type-I seesaw mechanism, while the mixing angles are predicted to be in their observed ranges due to the broken $L_μ-L_τ$ symmetry. The second complex scalar is shown to be stable and becomes the dark matter candidate in our model. We show that while the $Z_{μτ}$ portal is ineffective for the parameters needed to explain the anomalous muon $({\rm g-2})$ data, the correct dark matter relic abundance can easily be obtained from annihilation through the Higgs portal. Annihilation of the scalar dark matter in our model can also explain the Galactic Centre gamma ray excess observed by Fermi-LAT. We show the predictions of our model for future direct detection experiments and neutrino oscillation experiments.

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arXiv2016

Freeze-in Production of Sterile Neutrino Dark Matter in U(1)$_{\rm B-L}$ Model

With the advent of new and more sensitive direct detection experiments, scope for a thermal WIMP explanation of dark matter (DM) has become extremely constricted. The non-observation of thermal WIMP in these experiments has put a strong upper bound on WIMP-nucleon scattering cross section and within a few years it is likely to touch the neutrino floor. Hence in all probability, DM may have some non-thermal origin. In this work we explore in detail this possibility of a non-thermal sterile neutrino DM within the framework of U(1)$_{\rm B-L}$ model. The U(1)$_{\rm B-L}$ model on the other hand is a well-motivated and minimal way of extending the standard model so that it can explain the neutrino masses via Type-I see-saw mechanism. We have shown, besides explaining the neutrino mass, it can also accommodate a non-thermal sterile neutrino DM with correct relic density. In contrast with the existing literature, we have found that $W^\pm$ decay can also be a dominant production mode of the sterile neutrino DM. To obtain the comoving number density of dark matter, we have solved here a coupled set of Boltzmann equations considering all possible decay as well as annihilation production modes of the sterile neutrino dark matter. The framework developed here though has been done for a U(1)$_{\rm B-L}$ model, can be applied quite generally for any models with an extra neutral gauge boson and a fermionic non-thermal dark matter.

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arXiv2016

Galactic Gamma Ray Excess and Dark Matter Phenomenology in a $U(1)_{B-L}$ Model

In this work, we have considered a gauged $U(1)_{\rm B-L}$ extension of the Standard Model (SM) with three right handed neutrinos for anomaly cancellation and two additional SM singlet complex scalars with non-trivial B-L charges. One of these is used to spontaneously break the $U(1)_{\rm B-L}$ gauge symmetry, leading to Majorana masses for the neutrinos through the standard Type I seesaw mechanism, while the other becomes the dark matter (DM) candidate in the model. We test the viability of the model to simultaneously explain the DM relic density observed in the CMB data as well as the Galactic Centre (GC) $γ$-ray excess seen by Fermi-LAT. We show that for DM masses in the range 40-55 GeV and for a wide range of $U(1)_{\rm B-L}$ gauge boson masses, one can satisfy both these constraints if the additional neutral Higgs scalar has a mass around the resonance region. In studying the dark matter phenomenology and GC excess, we have taken into account theoretical as well as experimental constraints coming from vacuum stability condition, PLANCK bound on DM relic density, LHC and LUX and present allowed areas in the model parameter space consistent with all relevant data, calculate the predicted gamma ray flux from the GC and discuss the related phenomenology.

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arXiv2016

Possible explanation of indirect gamma ray signatures from hidden sector fermionic dark matter

We propose the existence of a hidden or dark sector besides the standard model (SM) of particle physics, whose members (both fermionic and bosonic) obey a local SU(2)$_{\rm H}$ gauge symmetry while behaving like a singlet under the SM gauge group. However, the fermiomic fields of the dark sector also possess another global U(1)$_{\rm H}$ symmetry which remains unbroken. The local SU(2)$_{\rm H}$ invariance of the dark sector is broken spontaneously when a scalar field in this sector acquires a vacuum expectation value (VEV) and thereby generating masses to the dark gauge bosons and dark fermions charged under the SU(2)$_{\rm H}$. The lightest fermion in this dark SU(2)$_{\rm H}$ sector can be a potential dark matter candidate. We first examine the viability of the model and constrain the model parameter space by theoretical constraints such as vacuum stability and by the experimental constraints such as PLANCK limit on relic density, LHC data, limits on spin independent scattering cross-section from dark matter direct search experiments etc. We then investigate the gamma rays from the pair annihilation of the proposed dark matter candidate at the Galactic Centre region. We also extend our calculations of gamma rays flux for the case of dwarf galaxies and compare the signatures of gamma rays obtained from these astrophysical sites.

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