arXiv subjects

Rahul Srivastava

Publications and source records attributed to Rahul Srivastava.

At least 91 records · Page 5Linked to original sources

arXiv2017

Generalized Bottom-Tau unification, neutrino oscillations and dark matter: predictions from a lepton quarticity flavor approach

We propose an $A_4$ extension of the Standard Model with a Lepton Quarticity symmetry correlating dark matter stability with the Dirac nature of neutrinos. The flavor symmetry predicts (i) a generalized bottom-tau mass relation involving all families, (ii) small neutrino masses are induced a la seesaw, (iii) CP must be significantly violated in neutrino oscillations, (iv) the atmospheric angle $θ_{23}$ lies in the second octant, and (v) only the normal neutrino mass ordering is realized.

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arXiv2017

Precise predictions for Dirac neutrino mixing

The neutrino mixing parameters are thoroughly studied using renormalization-group evolution of Dirac neutrinos with recently proposed parametrization of the neutrino mixing angles referred as `high-scale mixing relations'. The correlations among all neutrino mixing and $CP$ violating observables are investigated. The predictions for the neutrino mixing angle $θ_{23}$ are precise, and could be easily tested by ongoing and future experiments. We observe that the high scale mixing unification hypothesis is incompatible with Dirac neutrinos due to updated experimental data.

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arXiv2017

Probing anomalous Higgs couplings in $H \to Z V$ decays

We analyze the possibility of probing anomalous Higgs couplings in the rare decays $H \to Z V$, $V$ being a vector quarkonium state. These rare decays involve both gauge as well as the Yukawa sectors and either of them can potentially be anomalous. We show that the branching fractions for $H \to Z V$ decays in Standard Model are small, making it a sensitive probe for anomalous Higgs couplings originating from physics beyond Standard Model. Moreover, as both $V$ and $Z$ can decay into pair of charged leptons, they provide experimentally clean channels and future LHC runs should observe such decays. We perform a model independent analysis and show how angular asymmetries can be used to probe these anomalous Higgs couplings, taking further decays of $V$ and $Z$ to pair of charged leptons into account. The angular asymmetries can provide significant information about anomalous Higgs couplings in both gauge and Yukawa sectors.

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arXiv2016

CP Violation from Flavor Symmetry in a Lepton Quarticity Dark Matter Model

We propose a simple $Δ(27) \otimes Z_4$ model where neutrinos are predicted to be Dirac fermions. The smallness of their masses follows from a type-I seesaw mechanism and the leptonic CP violating phase correlates with the pattern of $Δ(27)$ flavor symmetry breaking. The scheme naturally harbors a WIMP dark matter candidate associated to the Dirac nature of neutrinos, in that the same $Z_4$ lepton number symmetry also ensures dark matter stability.

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arXiv2016

Constraining wrong-sign $hbb$ couplings with $h \rightarrow Υγ$

The rare decay $h \rightarrow Υγ$ has a very small rate in the Standard Model, due to a strong cancellation between the direct and indirect diagrams. Models with a changed $hbb$ coupling can thus lead to a great increase in this decay. Current limits on two Higgs doublet models still allow for the possibility that the $hbb$ coupling might have a sign opposite to the Standard Model; the so-called "wrong-sign". We show how $h \rightarrow Υγ$ can be used to put limits on the wrong-sign solutions.

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arXiv2016

Dirac Neutrinos and Dark Matter Stability from Lepton Quarticity

We propose to relate dark matter stability to the possible Dirac nature of neutrinos. The idea is illustrated in a simple scheme where small Dirac neutrino masses arise from a type--I seesaw mechanism as a result of a $Z_4$ discrete lepton number symmetry. The latter implies the existence of a viable WIMP dark matter candidate, whose stability arises from the same symmetry which ensures the Diracness of neutrinos.

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arXiv2016

750 GeV Diphoton excess from Gauged $B-L$ Symmetry

We show that the recently observed 750 GeV diphoton excess at LHC can be due to the decay of a $SU(2)_L$ singlet scalar particle having 3 units of charge under gauged $B - L$ symmetry. Such a particle arises as an essential ingredient of recently studied gauged $B -L$ extension of the Standard Model with unconventional charge assignment for right handed neutrinos. Apart from being one of the simplest extensions of the Standard Model, the model also contains a dark matter candidate and Dirac neutrinos with naturally small masses.

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arXiv2016

High scale mixing relations as a natural explanation for large neutrino mixing

The origin of small mixing among the quarks and a large mixing among the neutrinos has been an open question in particle physics. In order to answer this question, we postulate general relations among the quarks and the leptonic mixing angles at a high scale, which could be the scale of Grand Unified Theories. The central idea of these relations is that the quark and the leptonic mixing angles can be unified at some high scale either due to some quark-lepton symmetry or some other underlying mechanism and as a consequence, the mixing angles of the leptonic sector are proportional to that of the quark sector. We investigate the phenomenology of the possible relations where the leptonic mixing angles are proportional to the quark mixing angles at the unification scale by taking into account the latest experimental constraints from the neutrino sector. These relations are able to explain the pattern of leptonic mixing at the low scale and thereby hint that these relations could be possible signatures of a quark-lepton symmetry or some other underlying quark-lepton mixing unification mechanism at some high scale linked to Grand Unified Theories.

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arXiv2016

A flavour physics scenario for the 750 GeV diphoton anomaly

A simple variant of a realistic flavour symmetry scheme for fermion masses and mixings provides a possible interpretation of the diphoton anomaly as an electroweak singlet "flavon". The existence of TeV scale vector-like T-quarks required to provide adequate values for CKM parameters can also naturally account for the diphoton anomaly. Correlations between $V_{ub}$ and $V_{cb}$ with the vector-like T-quark mass can be predicted. Should the diphoton anomaly survive in a future Run, our proposed interpretation can also be tested in upcoming B and LHC studies.

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arXiv2015

Gauge $B-L$ Model with Residual $Z_3$ Symmetry

We study a gauge $B-L$ extension of the standard model of quarks and leptons with unconventional charges for the singlet right-handed neutrinos, and extra singlet scalars, such that a residual $Z_3$ symmetry remains after the spontaneous breaking of $B-L$. We discuss the phenomenological consequences of this scenario, including the possibility of long-lived self-interacting dark matter and $Z'$ collider signatures.

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arXiv2015

High Scale Mixing Unification for Dirac Neutrinos

Starting with high scale mixing unification hypothesis, we investigate the renormalization group evolution of mixing parameters and masses for Dirac type neutrinos. Following this hypothesis, the PMNS mixing angles and phase are taken to be identical to the CKM ones at a unifying high scale. Then, they are evolved to a low scale using renormalization-group equations. The notable feature of this hypothesis is that renormalization group evolution with quasi-degenerate mass pattern can explain largeness of leptonic mixing angles even for Dirac neutrinos. The renormalization group evolution "naturally" results in a non-zero and small value of leptonic mixing angle $θ_{13}$. One of the important predictions of this work is that the mixing angle $θ_{23}$ is non-maximal and lies only in the second octant. We also derive constraints on the allowed parameter range for the SUSY breaking and unification scales for which this hypothesis works. The results are novel and can be tested by present and future experiments.

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arXiv2015

Predictions From High Scale Mixing Unification Hypothesis

Starting with 'High Scale Mixing Unification' hypothesis, we investigate the renormalization group evolution of mixing parameters and masses for both Dirac and Majorana type neutrinos. Following this hypothesis, the PMNS mixing parameters are taken to be identical to the CKM ones at a unifying high scale. Then, they are evolved to a low scale using MSSM renormalization-group equations. For both type of neutrinos, the renormalization group evolution 'naturally' results in a non-zero and small value of leptonic mixing angle $θ_{13}$. One of the important predictions of this analysis is that, in both cases, the mixing angle $θ_{23}$ turns out to be non-maximal for most of the parameter range. We also elaborate on the important differences between Dirac and Majorana neutrinos within our framework and how to experimentally distinguish between the two scenarios. Furthermore, for both cases, we also derive constraints on the allowed parameter range for the SUSY breaking and unification scales, for which this hypothesis works. The results can be tested by present and future experiments.

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arXiv2015

Dirac or Inverse Seesaw Neutrino Masses from Gauged B - L Symmetry

The gauged $B - L$ symmetry is one of the simplest and well studied extension of standard model. In the conventional case, addition of three singlet right handed neutrinos each transforming as $-1$ under the $B - L$ symmetry renders it anomaly free. It is usually assumed that the $B - L$ symmetry is spontaneously broken by a singlet scalar having two units of $B - L$ charge, resulting in a natural implementation of Majorana seesaw mechanism for neutrinos. However, as we discuss in this proceeding, there is another simple anomaly free solution which leads to Dirac or inverse seesaw masses for neutrinos. These new possibilities are explored along with an application to neutrino mixing with $S_3$ flavour symmetry.

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arXiv2014

Dirac or Inverse Seesaw Neutrino Masses with $B-L$ Gauge Symmetry and $S_3$ Flavour Symmetry

Many studies have been made on extensions of the standard model with $B-L$ gauge symmetry. The addition of three singlet (right-handed) neutrinos renders it anomaly-free. It has always been assumed that the spontaneous breaking of $B-L$ is accomplished by a singlet scalar field carrying two units of $B-L$ charge. This results in a very natural implementation of the Majorana seesaw mechanism for neutrinos. However, there exists in fact another simple anomaly-free solution which allows Dirac or inverse seesaw neutrino masses. We show for the first time these new possibilities and discuss an application to neutrino mixing with $S_3$ flavour symmetry.

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arXiv2014

Predictions from High Scale Mixing Unification Hypothesis

We investigate the renormalization group evolution of masses and mixing angles of Majorana neutrinos under the `High Scale Mixing Unification' hypothesis. Assuming the unification of quark-lepton mixing angles at a high scale, we show that all the experimentally observed neutrino oscillation parameters can be obtained, within 3-$σ$ range, through the running of corresponding renormalization group equations provided neutrinos have same CP parity and are quasi-degenerate. One of the novel results of our analysis is that $θ_{23}$ turns out to be non-maximal and lies in the second octant. Furthermore, we derive new constraints on the allowed parameter space for the unification scale, SUSY breaking scale and $\tan β$, for which the `High Scale Mixing Unification' hypothesis works.

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arXiv2013

Spin-Statistics Correlations in Various Noncommutative Field Theories

In this thesis we study field theories written on a particular model of noncommutative spacetime, the Groenewold-Moyal (GM) plane. We start with briefly reviewing the novel features of field theories on GM plane e.g. the $\ast$-product, restoration of Poincaré-Hopf symmetry and twisted commutation relations. We then discuss our work on renormalization of field theories on GM plane. We show that any generic noncommutative theory involving pure matter fields with polynomial interactions, is a renormalizable theory if the analogous commutative theory is renormalizable. We further show that all such noncommutative theories will have same fixed points and $β$-functions for the couplings, as that of the analogous commutative theory. The unique feature of these field theories is the twisted statistics obeyed by the particles. Motivated by it, we look at the possibility of twisted statistics by deforming internal symmetries instead of spacetime symmetries. We construct two different twisted theories which can be viewed as internal symmetry analogue of the GM plane and dipole field theories which arise in the low energy limit of certain string configurations. We further study their various properties like the issue of causality and the scattering formalism. Having studied the mathematical properties of noncommutative and twisted internal symmetries we move on to discuss their potential phenomenological signatures. We first discuss the noncommutative thermal correlation functions and show that because of the twisted statistics, all correlation functions except two-point function get modified. Finally we discuss the modifications in Hanbury-Brown Twiss (HBT) correlation functions due to twisted statistics on GM plane and the potential of observing signatures of noncommutativity by doing a HBT correlation experiment with Ultra High Energy Cosmic Rays (UHECRs).

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arXiv2013

Poincaré Invariant Quantum Field Theories With Twisted Internal Symmetries

Following up the work of [1] on deformed algebras, we present a class of Poincaré invariant quantum field theories with particles having deformed internal symmetries. The twisted quantum fields discussed in this work satisfy commutation relations different from the usual bosonic/fermionic commutation relations. Such twisted fields by construction are nonlocal in nature. Despite this nonlocality we show that it is possible to construct local interaction Hamiltonians which satisfy cluster decomposition principle and are Lorentz invariant. We further illustrate these ideas by considering global SU(N) symmetries. Specifically we show that twisted internal symmetries can significantly simplify the discussion of the marginal deformations (β-deformations) of the N=4 SUSY theories.

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arXiv2013

Renormalization of Noncommutative Quantum Field Theories

We report on a comprehensive analysis of the renormalization of noncommutative ϕ^4 scalar field theories on the Groenewold-Moyal (GM) plane. These scalar field theories are twisted Poincaré invariant. Our main results are that these scalar field theories are renormalizable, free of UV/IR mixing, possess the same fixed points and β-functions for the couplings as their commutative counterparts. We also argue that similar results hold true for any generic noncommutative field theory with polynomial interactions and involving only pure matter fields. A secondary aim of this work is to provide a comprehensive review of different approaches for the computation of the noncommutative S-matrix: noncommutative interaction picture and noncommutative LSZ formalism.

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