Ujjal Kumar Dey

Universal Extra-Dimensional Models with Boundary Localized Kinetic Terms: Probing at the LHC

In universal extra-dimensional models a conserved

Constraining minimal and nonminimal universal extra dimension models with Higgs couplings

Z_2

Light Dark Matter through Assisted Annihilation

parity ensures the stability of the lightest Kaluza-Klein particle, a potential dark-matter candidate. We show here that boundary-localized kinetic terms, in general, do not preserve this symmetry. We examine the single production of a Kaluza-Klein excitation of the photon and its decay to zero-mode fermion-antifermion pairs in the presence of such terms. We explore how experiments at the Large Hadron Collider at CERN can help constrain the boundary-localized kinetic terms for different choices of the compactification radius.

Rare top decays in minimal and nonminimal universal extra dimension models

Early indications from the LHC for the observed scalar boson imply properties close to the Standard Model Higgs, putting considerable constraints on TeV scale new physics scenarios. In this letter we consider flat extra dimensional scenarios with the fifth spatial dimen sion compactified on an S 1 /Z2 orbifold. We find in the minimal model the experimentally preferred effective Higgs couplings to gluon and photon at 95% confidence level disfavor the New Physics scale below 1.3 TeV. We demonstrate that a generalization of these models to include brane localized kinetic terms can relieve the tension to accommodate scales as low as 0.4 TeV.

Multi-component fermionic dark matter and IceCube PeV scale neutrinos in left-right model with gauge unification

In this paper we investigate light dark matter scenarios where annihilation to Standard Model particles at tree-level is kinematically forbidden. In such cases annihilation can be aided by massive Standard Model-like species, called {\it assisters}, in the initial state that enhances the available phase space opening up novel tree-level processes. We investigate the feasibility of such non-standard {\it assisted annihilation} processes to reproduce the observed relic density of dark matter. We present a simple scalar dark matter - scalar assister model where this is realised. We find that if the dark matter and assister are relatively degenerate the required relic density can be achieved for a keV-MeV scale dark matter. We briefly discuss the cosmological constraints on such dark matter scenarios.

Effects of QCD equation of state on the stochastic gravitational wave background

The avour changing decays of the top quark are severely suppressed in the Standard Model by virtue of GIM mechanism. Many beyond Standard Model extensions predict the decay rates at a level which is observable in the LHC. We perform a complete one-loop calculation of the avour changing top quark decays t! c and t! ch in the universal extra dimensional model. Apart from considering the decay rates in minimal version of the model, we also calculate the rates in the non-minimal scenario where the presence of boundary localised terms interestingly modify the set-up. We nd that the decay rates in the minimal variant of the model do not change much from their Standard Model values. However in the non-minimal version of the model these decay rates can be higher for specic choice of the boundary localised parameters.

Higgs-Gluon Coupling in Warped Extra Dimensional Models with Brane Kinetic Terms

A bstractWe consider a simple extension of the minimal left-right symmetric model (LRSM) in order to explain the PeV neutrino events seen at the IceCube experiment from a heavy decaying dark matter. The dark matter sector is composed of two fermions: one at PeV scale and the other at TeV scale such that the heavier one can decay into the lighter one and two neutrinos. The gauge annihilation cross sections of PeV dark matter are not large enough to generate its relic abundance within the observed limit. We include a pair of real scalar triplets ΩL,R which can bring the thermally overproduced PeV dark matter abundance into the observed range through late time decay and consequent entropy release thereby providing a consistent way to obtain the correct relic abundance without violating the unitarity bound on dark matter mass. Another scalar field, a bitriplet under left-right gauge group is added to assist the heavier dark matter decay. The presence of an approximate global U(1)X symmetry can naturally explain the origin of tiny couplings required for long-lived nature of these decaying particles. We also show, how such an extended LRSM can be incorporated within a non-supersymmetric SO(10) model where the gauge coupling unification at a very high scale naturally accommodate a PeV scale intermediate symmetry, required to explain the PeV events at IceCube.

Status of Flavour Maximal Non-minimal Universal Extra Dimension

Cosmological phase transitions can be a source of Stochastic Gravitational Wave (SGW) background. Apart from the dynamics of the phase transition, the characteristic frequency and the fractional energy density

Quark mixing in an

\Omega_{\rm gw}

S_3

of the SGW depends upon the temperature of the transition. In this article, we compute the SGW spectrum in the light of QCD equation of state provided by the lattice results. We find that the inclusion of trace anomaly from lattice QCD, enhances the SGW signal generated during QCD phase transition by