Nirakar Sahoo - Academia.edu (original) (raw)
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Papers by Nirakar Sahoo
Physical Review D, 2017
We propose a minimal extension of the standard model (SM) by including a scalar triplet with hype... more We propose a minimal extension of the standard model (SM) by including a scalar triplet with hypercharge 2 and two vector-like leptons: one doublet and a singlet, to explain simulatenously the non-zero neutrino mass and dark matter (DM) content of the Universe. The DM emerges out as a mixture of the neutral component of vector-like lepton doublet and singlet, being odd under a discrete Z2 symmetry. After electroweak symmetry breaking the triplet scalar gets an induced vev, which give Majorana masses not only to the light neutrinos but also to the DM. Due to the Majorana mass of DM, the Z mediated elastic scattering with nucleon is forbidden. However, the Higgs mediated direct detection cross-section of the DM gives an excellent opportunity to probe it at Xenon-1T. The DM can not be detected at collider. However, the charged partner of the DM (often next-to-lightest stable particle) can give large dispalced vertex signature at the Large Hadron Collider (LHC).
Frontiers in Physics, 2019
We review a class of models in which the Standard Model (SM) is augmented by vector-like leptons:... more We review a class of models in which the Standard Model (SM) is augmented by vector-like leptons: one doublet and a singlet, which are odd under an unbroken discrete Z 2 symmetry. As a result, the neutral component of these additional vector-like leptons are stable and behave as dark matter. We study the phenomenological constraints on the model parameters and elucidate the parameter space for relic density, direct detection and collider signatures of dark matter. In such models, we further add a scalar triplet of hypercharge two and study the consequences. In particular, after electro weak symmetry breaking (EWSB), the triplet scalar gets an induced vacuum expectation value (vev), which yield Majorana masses not only to the light neutrinos but also to vector-like leptonic doublet DM. Due to the Majorana mass of DM, the Z mediated elastic scattering with nucleon is forbidden and hence allowing the model to survive from stringent direct search bound. The DM without scalar triplet lives in a small singlet-doublet leptonic mixing region (sin θ ≤ 0.1) due to large contribution from singlet component and have small mass difference (m ∼ 10 GeV) with charged companion, the NLSP (next to lightest stable particle), to aid co-annihilation for yielding correct relic density. Both these observations change to certain extent in presence of scalar triplet to aid observability of hadronically quiet leptonic final states at LHC, while one may also confirm/rule-out the model through displaced vertex signal of NLSP, a characteristic signature of the model in relic density and direct search allowed parameter space.
We have explored an extended seesaw model accommodating a keV sterile neutrino adopting U(1)B−L s... more We have explored an extended seesaw model accommodating a keV sterile neutrino adopting U(1)B−L symmetry. This model provides a natural platform for achieving resonant leptogenesis to account for the observed baryon asymmetry of the Universe. The required lepton asymmetry is sourced by the CP violating decay of the lightest heavy right handed neutrino to Standard Model leptons and Higgs. The presence of the light sterile neutrino in the model brings out an enhancement in the final lepton asymmetry through an additional self-energy contribution. Adopting a proper treatment for all the washout processes this framework strictly favours a strong washout regime thereby protecting the low energy neutrino mass parameters in agreement with the present neutrino and cosmology data. This framework of extended seesaw scheme offers the source of matter-antimatter asymmetry without any severe fine tuning of the Yukawa couplings governing the tiny neutrino mass. We also comment on the half-life pe...
Physical Review D, 2017
We propose a minimal extension of the standard model (SM) by including a scalar triplet with hype... more We propose a minimal extension of the standard model (SM) by including a scalar triplet with hypercharge 2 and two vector-like leptons: one doublet and a singlet, to explain simulatenously the non-zero neutrino mass and dark matter (DM) content of the Universe. The DM emerges out as a mixture of the neutral component of vector-like lepton doublet and singlet, being odd under a discrete Z2 symmetry. After electroweak symmetry breaking the triplet scalar gets an induced vev, which give Majorana masses not only to the light neutrinos but also to the DM. Due to the Majorana mass of DM, the Z mediated elastic scattering with nucleon is forbidden. However, the Higgs mediated direct detection cross-section of the DM gives an excellent opportunity to probe it at Xenon-1T. The DM can not be detected at collider. However, the charged partner of the DM (often next-to-lightest stable particle) can give large dispalced vertex signature at the Large Hadron Collider (LHC).
Frontiers in Physics, 2019
We review a class of models in which the Standard Model (SM) is augmented by vector-like leptons:... more We review a class of models in which the Standard Model (SM) is augmented by vector-like leptons: one doublet and a singlet, which are odd under an unbroken discrete Z 2 symmetry. As a result, the neutral component of these additional vector-like leptons are stable and behave as dark matter. We study the phenomenological constraints on the model parameters and elucidate the parameter space for relic density, direct detection and collider signatures of dark matter. In such models, we further add a scalar triplet of hypercharge two and study the consequences. In particular, after electro weak symmetry breaking (EWSB), the triplet scalar gets an induced vacuum expectation value (vev), which yield Majorana masses not only to the light neutrinos but also to vector-like leptonic doublet DM. Due to the Majorana mass of DM, the Z mediated elastic scattering with nucleon is forbidden and hence allowing the model to survive from stringent direct search bound. The DM without scalar triplet lives in a small singlet-doublet leptonic mixing region (sin θ ≤ 0.1) due to large contribution from singlet component and have small mass difference (m ∼ 10 GeV) with charged companion, the NLSP (next to lightest stable particle), to aid co-annihilation for yielding correct relic density. Both these observations change to certain extent in presence of scalar triplet to aid observability of hadronically quiet leptonic final states at LHC, while one may also confirm/rule-out the model through displaced vertex signal of NLSP, a characteristic signature of the model in relic density and direct search allowed parameter space.
We have explored an extended seesaw model accommodating a keV sterile neutrino adopting U(1)B−L s... more We have explored an extended seesaw model accommodating a keV sterile neutrino adopting U(1)B−L symmetry. This model provides a natural platform for achieving resonant leptogenesis to account for the observed baryon asymmetry of the Universe. The required lepton asymmetry is sourced by the CP violating decay of the lightest heavy right handed neutrino to Standard Model leptons and Higgs. The presence of the light sterile neutrino in the model brings out an enhancement in the final lepton asymmetry through an additional self-energy contribution. Adopting a proper treatment for all the washout processes this framework strictly favours a strong washout regime thereby protecting the low energy neutrino mass parameters in agreement with the present neutrino and cosmology data. This framework of extended seesaw scheme offers the source of matter-antimatter asymmetry without any severe fine tuning of the Yukawa couplings governing the tiny neutrino mass. We also comment on the half-life pe...