arXiv subjects

Chandan Hati

Publications and source records attributed to Chandan Hati.

At least 37 records · Page 2Linked to original sources

arXiv2021

Scotogenic neutrino masses with gauged matter parity and gauge coupling unification

Building up on previous work we propose a Dark Matter (DM) model with gauged matter parity and dynamical gauge coupling unification, driven by the same physics responsible for scotogenic neutrino mass generation. Our construction is based on the extended gauge group \3311, whose spontaneous breaking leaves a residual conserved matter parity, $M_{P}$, stabilizing the DM particle candidates of the model. A key role is played by the Majorana ${\rm SU(3)_{L}}$-octet leptons, in allowing successful gauge coupling unification and one-loop scotogenic neutrino mass generation. Theoretical consistency allows for a \emph{plethora} of new particles at the $\lsim \mathcal{O}$(10) TeV scale, hence accessible to future collider and low-energy experiments.

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arXiv2020

Probing New Physics with Long-Range Neutrino Interactions: An Effective Field Theory Approach

We investigate forces induced by the exchange of two light neutrinos between Standard Model (SM) fermions in the presence of effective operators parametrising physics beyond the SM. We first set up a general framework in which we derive the long-range potential mediated by weakly interacting neutrinos in the SM, retaining both spin-independent and spin-dependent terms. We then derive neutrino-mediated potentials when there are vector, scalar and tensor non-standard interactions present as well as an exotic neutrino magnetic moment. Examining the phenomenology of such long-range potentials in atomic scale laboratory experiments, we derive upper bounds on the Wilson coefficients of the effective operators and compare these to those from processes such as charged lepton flavour violation.

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arXiv2020

$B-L$ violating nucleon decays as a probe of leptoquarks and implications for baryogenesis

We study the effective $B-L$ violating couplings for scalar and vector leptoquarks which can naturally induce dimension seven $B-L$ violating operators leading to very interesting nucleon decay modes such as $n \rightarrow e^- π^+, e^-K^+,μ^- π^+, μ^-K^+$ and $p \rightarrow νπ^+$. This opens a new window to probe the nature and couplings of the scalar and vector leptoquarks in an ultraviolet model independent way which can provide an orthogonal probe for scalar and vector leptoquark solutions to the recent anomalous $B$-decay data. Furthermore, we also discuss how these $B-L$ violating interactions can also pave a new way to understand the origin of matter-antimatter asymmetry of the Universe.

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arXiv2019

Alternative formulation of left-right symmetry with $B-L$ conservation and purely Dirac neutrinos

We propose an alternative formulation of a Left-Right Symmetric Model (LRSM) where the difference between baryon number ($B$) and lepton number ($L$) remains an unbroken symmetry. This is unlike the conventional formulation, where $B-L$ is promoted to a local symmetry and is broken explicitly in order to generate Majorana neutrino masses. In our case $B-L$ remains a global symmetry after the left-right symmetry breaking, allowing only Dirac mass terms for neutrinos. In addition to parity restoration at some high scale, this formulation provides a natural framework to explain $B-L$ as an anomaly-free global symmetry of the Standard Model and the non-observation of $(B-L)$-violating processes. Neutrino masses are purely Dirac type and are generated either through a two loop radiative mechanism or by implementing a Dirac seesaw mechanism.

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arXiv2019

Neutrinoless Double-$β$ Decay with Nonstandard Majoron Emission

We present a novel mode of neutrinoless double beta decay with emission of a light Majoron-like scalar particle phi. We assume it couples via an effective seven-dimensional operator with a (V+A) lepton current and (V+-A) quark currents leading to a long-range contribution that is unsuppressed by the light neutrino mass. We calculate the total double beta decay rate and determine the fully differential shape for this mode. We find that future double beta decay searches are sensitive to scales of the order Lambda_NP ~ 1 TeV for the effective operator and a light scalar m_phi < 0.2 MeV, based on ordinary double beta decay Majoron searches. The angular and energy distributions can deviate considerably from that of two-neutrino double beta decay, which is the main background. We point out possible ultraviolet completions where such an effective operator can emerge.

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arXiv2018

Reconciling $B$-meson Anomalies, Neutrino Masses and Dark Matter

We explore the connection of the leptoquark solution to the recently reported $B$-meson anomalies with a mechanism of neutrino mass generation and a viable dark matter candidate. We consider a model consisting of two scalar leptoquarks and three generations of triplet fermions: neutrino masses are radiatively generated at the 3-loop level and, by imposing a discrete $Z_2$ symmetry, one can obtain a viable dark matter candidate. We discuss the constraints on the flavour structure of this model arising from numerous flavour observables. The rare decay $K\to π^+ν\barν$ and charged lepton flavour violating $μ-e$ conversion in nuclei are found to provide the most stringent constraint on this class of models.

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arXiv2018

Reconciling $B$-decay anomalies with neutrino masses, dark matter and constraints from flavour violation

Motivated by an explanation of the $R_{K^{(*)}}$ anomalies, we propose a Standard Model extension via two scalar SU(2)$_L$ triplet leptoquarks and three generations of triplet Majorana fermions. The gauge group is reinforced by a $Z_2$ symmetry, ensuring the stability of the lightest $Z_2$-odd particle, which is a potentially viable dark matter candidate. Neutrino mass generation occurs radiatively (at the three-loop level), and leads to important constraints on the leptoquark couplings to leptons. We consider very generic textures for the flavour structure of the $h_1$ leptoquark Yukawa couplings, identifying classes of textures which succeed in saturating the $R_{K^{(*)}}$ anomalies. We subsequently carry a comprehensive analysis of the model's contributions to numerous high-intensity observables such as meson oscillations and decays, as well as charged lepton flavour violating processes, which put severe constraints on the flavour structure of these leptoquark extensions. Our findings suggest that the most constraining observables are $K^+ \to π^+ ν\bar ν$ decays, and charged lepton flavour violating $μ-e$ conversion in nuclei (among others). Nevertheless, for several classes of flavour textures and for wide mass regimes of the new mediators (within collider reach), this Standard Model extension successfully addresses neutrino mass generation, explains the current $R_{K^{(*)}}$ tensions, and offers a viable dark matter candidate.

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arXiv2017

Scrutinizing $R$-parity violating interactions in light of $R_{K^{(\ast)}}$ data

The LHCb has measured the ratios of $B\to K^\astμ^+μ^-$ to $B\to K^\ast e^+ e^-$ branching fractions in two dilepton invariant mass squared bins, which deviate from the Standard Model predictions by approximately $2.5σ$. These new measurements strengthen the hint of lepton flavor universality breaking which was observed earlier in $B\to K\ell^+\ell^-$ decays. In this work we explore the possibility of explaining these anomalies within the framework of $R$-parity violating interactions. In this framework, $b\to s\ell^+\ell^-$ transitions are generated through tree and one loop diagrams involving exchange of down-type right-handed squarks, up-type left-handed squarks and left-handed sneutrinos. We find that the tree level contributions are not enough to explain the anomalies, but at one loop, simultaneous explanation of the deviations in $B\to K^\ast\ell^+\ell^-$ and $B\to K\ell^+\ell^-$ is feasible for a parameter space of the Yukawa couplings that is consistent with the bounds coming from $B\to K^{(\ast)}ν\barν$ and $D^0\to μ^+μ^-$ decays and $B_s-\bar{B}_s$ mixing.

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arXiv2017

Towards gauge coupling unification in left-right symmetric $\mathrm{SU(3)_c \times SU(3)_L \times SU(3)_R \times U(1)_{X}}$ theories

We consider the possibility of gauge coupling unification within the simplest realizations of the $\mathrm{SU(3)_c \times SU(3)_L \times SU(3)_R \times U(1)_{X}}$ gauge theory. We present a first exploration of the renormalization group equations governing the "bottom-up" evolution of the gauge couplings in a generic model with free normalization for the generators. Interestingly, we find that for a $\mathrm{SU(3)_c \times SU(3)_L \times SU(3)_R \times U(1)_{X}}$ symmetry breaking scale $M_X$ as low as a few TeV one can achieve unification in the presence of leptonic octets. We briefly comment on possible grand unified theory frameworks which can embed the $\mathrm{SU(3)_c \times SU(3)_L \times SU(3)_R \times U(1)_{X}}$ model as well as possible implications, such as lepton flavour violating physics at the LHC.

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arXiv2017

Neutrinoless Double Beta Decay in Left-Right Symmetry with Universal Seesaw

We discuss a class of left-right symmetric theories with a universal seesaw mechanism for fermion masses and mixing and the implications for neutrinoless double beta ($0νββ$) decay where neutrino masses are governed by natural type-II seesaw dominance. The scalar sector consists of left- and right-handed Higgs doublets and triplets, while the conventional Higgs bidoublet is absent in this scenario. We use the Higgs doublets to implement the left-right and the electroweak symmetry breaking. On the other hand, the Higgs triplets with induced vacuum expectation values can give Majorana masses to light and heavy neutrinos and mediate $0νββ$ decay. In the absence of the Dirac mass terms for the neutrinos, this framework can naturally realize type-II seesaw dominance even if the right-handed neutrinos have masses of a few TeV. We study the implications of this framework in the context of $0νββ$ decay and gauge coupling unification.

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arXiv2016

Towards a unified explanation of $R_{D^{(\ast)}}$, $R_{K}$ and $(g-2)_μ$ anomalies in a left-right model with leptoquarks

We present a unified explanation for the $B$-decay anomalies in $R_{D^{(\ast)}}$ and $R_{K}$ together with the anomalous muon magnetic moment, consistent with the constraints from the current measurements of leptonic decay rates and $D^0-\bar{D}^0$, $B_{s}^0-\bar{B}_{s}^0$ mixings, within the framework of a minimal left-right symmetric gauge theory motivated by one of the low-energy subgroups of $E_{6}$ naturally accommodating leptoquarks.

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arXiv2016

331 Models and Grand Unification: From Minimal SU(5) to Minimal SU(6)

We consider the possibility of grand unification of the $\mathrm{ SU(3)_c \otimes SU(3)_L \otimes U(1)_X}$ model in an SU(6) gauge unification group. Two possibilities arise. Unlike other conventional grand unified theories, in SU(6) one can embed the $\mathrm{ SU(3)_c \otimes SU(3)_L \otimes U(1)_X}$ model as a subgroup such that different multiplets appear with different multiplicities. Such a scenario may emerge from the flux breaking of the unified group in an E(6) F-theory GUT. This provides new ways of achieving gauge coupling unification in $\mathrm{ SU(3)_c \otimes SU(3)_L \otimes U(1)_X}$ models while providing the radiative origin of neutrino masses. Alternatively, a sequential variant of the $\mathrm{ SU(3)_c \otimes SU(3)_L \otimes U(1)_X}$ model can fit within a minimal SU(6) grand unification, which in turn can be a natural E(6) subgroup. This minimal SU(6) embedding does not require any bulk exotics to account for the chiral families while allowing for a TeV scale $\mathrm{ SU(3)_c \otimes SU(3)_L \otimes U(1)_X}$ model with seesaw-type neutrino masses.

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arXiv2016

A minimal model of TeV scale WIMPy leptogenesis

We present a minimal framework of $U(1)_{B-L}$ gauge extension of the Standard Model explaining dark matter abundance and matter-antimatter asymmetry simultaneously through an attractive mechanism of TeV scale WIMPy leptogenesis, testable at the current and next generation of colliders. This framework can also explain small neutrino masses via a radiative mechanism. One of the key predictions of this model is an enhanced rate for lepton flavor violating decay $μ\rightarrow e γ$ within the sensitivity reach of next generation experiments.

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arXiv2016

Implications of the diphoton excess on Left-Right models and gauge unification

The recent diphoton excess signal at an invariant mass of 750 GeV can be interpreted in the framework of left-right symmetric models with additional scalar singlets and vector-like fermions. We propose a minimal scenario for such a purpose. Extending the LRSM framework to include these new vector-like fermionic fields, on the other hand, results in interesting phenomenological implications for the LRSM fermion masses and mixing. Furthermore, existence of such vector-like fermions can also have interesting implications for baryogenesis and the dark matter sector. The introduction of a real bi-triplet scalar which contains a potential DM candidate will allow the gauge couplings to unify at $\approx 10^{17.7}$ GeV.

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arXiv2016

Explaining the diphoton excess in Alternative Left-Right Symmetric Model

We propose a possible explanation of the recent diphoton excess reported by ATLAS and CMS collaborations, at around 750 GeV diphoton invariant mass, within the framework of $E_{6}$ motivated Alternative Left-Right Symmetric Model (ALRSM), which is capable of addressing the $B$ decay anomalies in the flavor sector, the $eejj$ and $e$ missing $p_{T}jj$ excesses reported by CMS in run 1 of LHC and has the feature of high scale leptogenesis. We find that gluon-gluon fusion can give the observed production rate of the 750 GeV resonance, $\tilde{n}$, through a loop of scalar leptoquarks ($\tilde{h}^{(c)}$) with mass below a few TeV range, while $\tilde{n}$ can subsequently decay into $γγ$ final state via loops of $\tilde{h}^{(c)}$ and $\tilde{E}^{(c)}$. Interestingly, the $\tilde{E}^{(c)}$ loop can enhance the diphoton branching ratio significantly to successfully explain the observed cross section of the diphoton signal.

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arXiv2015

$\bar{B}\rightarrow D^{(\ast)}τ\barν$ excesses in ALRSM constrained from $B$, $D$ decays and $D^{0}-\bar{D}^{0}$ mixing

Recent experimental results from the LHCb, BaBar and Belle collaborations on the semitauonic decays of $B$ meson, $\bar{B}\rightarrow D^{(\ast)}τ\barν$, showing a significant deviation from the Standard Model (SM), hint towards a new physics scenario beyond the SM. In this work, we show that these enhanced decay rates can be explained within the framework of $E_{6}$ motivated Alternative Left-Right Symmetric Model (ALRSM), which has been successful in explaining the recent CMS excesses and has the feature of accommodating high scale leptogenesis. The R-parity conserving couplings in ALRSM can contribute universally to both $\bar{B}\rightarrow D τ\barν$ and $\bar{B}\rightarrow D^{(\ast)}τ\barν$ via the exchange of scalar leptoquarks. We study the leptonic decays $D_{s}^{+} \rightarrow τ^{+} \barν$, $B^{+}\rightarrow τ^{+} \barν$, $D^{+}\rightarrow τ^{+} \barν$ and $D^{0}$-$\bar{D}^{0}$ mixing to constrain the couplings involved in explaining the enhanced $B$ decay rates and we find that ALRSM can explain the current experimental data on $\mathcal{R}(D^{(\ast)})$ quite well while satisfying these constraints.

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arXiv2015

Neutrino dark energy and leptogenesis with TeV scale triplets

We propose a realization of mass varying neutrino dark energy in two extensions of the Standard Model (SM) with a dynamical neutrino mass related to the acceleron field while satisfying the naturalness. In the first scenario the SM is extended to include a TeV scale scalar Higgs triplet ($ξ$) and a TeV scale second Higgs doublet ($η$), while in the second scenario an extension of the SM with fermion triplet $(Σ)$ is considered. We also point out the possible leptogenesis mechanisms for simultaneously generating the observed baryon asymmetry of the universe in both the scenarios and discuss the collider signatures for the TeV scale new fields which make these models testable in the current run of LHC.

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arXiv2015

Falsifying leptogenesis for a TeV scale $W^{\pm}_{R}$ at the LHC

We point out that the discovery of a right-handed charged gauge boson $W_R^\pm$ with mass of around a few TeV, for example through a signal of two leptons and two jets that has been reported by CMS to have a 2.8$σ$ local excess or through a signal of a resonance decaying into a pair of standard model (SM) gauge bosons showing a local excess of 3.4$σ$ (2.5$σ$ global) reported by ATLAS search, will rule out all possibilities of leptogenesis in all classes of the left-right symmetric extensions of the Standard Model (LRSM) with both triplet and doublet Higgs scalars due to the unavoidable fast gauge mediated $B-L$ violating interactions $e_{R}^{\pm} W_{R}^{\mp} \rightarrow e_{R}^{\mp} W_{R}^{\pm}$. Our conclusions are very general in the sense that they do not necessarily demand for a lepton number violating detection signal of $W_R^\pm$.

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