arXiv subjects

Narendra Sahu

Publications and source records attributed to Narendra Sahu.

At least 109 records · Page 6Linked to original sources

arXiv2008

Gravitino production in an inflationary Universe and implications for leptogenesis

Models of leptogenesis are constrained by the low reheat temperature at the end of reheating associated with the gravitino bound. However a detailed view of reheating, in which the maximum temperature during reheating, $\Tmax$, can be orders of magnitude higher than the reheat temperature, allows for the production of heavy Majorana neutrinos needed for leptogenesis. But then one must also consider the possibility of enhanced gravitino production in such scenarios. In this article we consider gravitino production during reheating, its dependence on $\Tmax$, and its relevance for leptogenesis. Earlier analytical studies of the gravitino abundance have only considered gravitino production in the post-reheating radiation dominated era. We find that the gravitino abundance generated during reheating is comparable to that generated after reheating. This lowers the upper bound on the reheat temperature by a factor of 4/3.

hep-ph↗

arXiv2008

Type-II Seesaw at Collider, Lepton Asymmetry and Singlet Scalar Dark Matter

We propose an extension of the standard model with a B-L global symmetry that is broken softly at the TeV scale. The neutrinos acquire masses through a type-II seesaw while the lepton (L) asymmetry arises in the {\it singlet sector} but without B-L violation. The model has the virtue that the scale of L-number violation ($Λ$) giving rise to neutrino masses is independent of the scale of leptogenesis ($Λ'$). As a result the model can explain {\it neutrino masses, singlet scalar dark matter and leptogenesis at the TeV scale}. The stability of the dark matter is ensured by a surviving $Z_2$ symmetry, which could be lifted at the Planck scale and thereby allowing Planck scale-suppressed decay of singlet scalar dark matter particles of mass $\approx 3$ MeV to $e^+ e^-$ pairs in the Galactic halo. The model also predicts a few hundred GeV doubly charged scalar and a long lived charged fermion, whose decay can be studied at Large Hadron Collider (LHC) and International Linear Collider (ILC).

hep-ph↗

arXiv2007

Inflation in minimal left-right symmetric model with spontaneous D-parity breaking

We present a simplest inflationary scenario in the minimal left-right symmetric model with spontaneous D-parity breaking, which is a well motivated particle physics model for neutrino masses. This leads us to connect the observed anisotropies in the cosmic microwave background to the sub-eV neutrino masses. The baryon asymmetry via the leptogenesis route is also discussed briefly.

hep-ph↗

arXiv2007

Fermion Number Fractionization

Solitons emerge as non-perturbative solutions of non-linear wave equations in classical and quantum theories. These are non-dispersive and localised packets of energy-remarkable properties for solutions of non-linear differential equations. In presence of such objects, the solutions of Dirac equation lead to the curious phenomenon of "fractional fermion number", a number which under normal conditions takes strictly integral values. In this article, we describe this accidental discovery and its manifestation in polyacetylene chains, which has lead to the development of organic conductors.

physics.pop-ph↗

arXiv2007

Predictive model for dark matter, dark energy, neutrino masses and leptogenesis at the TeV scale

We propose a new mechanism of TeV scale leptogenesis where the chemical potential of right-handed electron is passed on to the $B-L$ asymmetry of the Universe in the presence of sphalerons. The model has the virtue that the origin of neutrino masses are independent of the scale of leptogenesis. As a result, the model could be extended to explain {\it dark matter, dark energy, neutrino masses and leptogenesis at the TeV scale}. The most attractive feature of this model is that it predicts a few hundred GeV triplet Higgs scalar that can be tested at LHC or ILC.

hep-ph↗

arXiv2007

TeV scale model for neutrino masses, dark matter and leptogenesis

We present a TeV scale model for leptogenesis where the origin of neutrino masses are independent of the scale of leptogenesis. As a result, the model could be extended to explain {\it dark matter, neutrino masses and leptogenesis at the TeV scale}. The most attractive feature of this model is that it predicts a few hundred GeV triplet Higgs scalar that can be tested at LHC or ILC.

hep-ph↗

arXiv2007

Soliton-fermion systems and stabilised vortex loops

In several self-coupled quantum field theories when treated in semi-classical limit one obtains solitonic solutions determined by topology of the boundary conditions. Such solutions, e.g. magnetic monopole in unified theories \cite{Hooft1974} \cite{Polyakov1974} or the skyrme model of hadrons have been proposed as possible non-perturbative bound states which remain stable due to topological quantum numbers. Furthermore when fermions are introduced, under certain conditions one obtains zero-energy solutions \cite{Vega1978}\cite{Jackiw1981} for the Dirac equations localised on the soliton. An implication of such zero-modes is induced fermion number \cite{Jackiw1977} carried by the soliton.

hep-ph↗

arXiv2006

Low-Energy Thermal Leptogenesis in an Extended NMSSM Model

Thermal leptogenesis in the canonical seesaw model in supersymmetry suffers from the incompatibility of a generic lower bound on the mass scale of the lightest right-handed neutrino and the upper bound on the reheating temperature of the Universe after inflation. This is resolved by adding an extra singlet superfield, with a discrete $Z_2$ symmetry, to the NMSSM (Next to Minimal Supersymmetric Standard Model). This generic mechanism is applicable to any supersymmetric model for lowering the scale of leptogenesis.

hep-ph↗

arXiv2006

Leptogenesis bound on neutrino masses in left-right symmetric models with spontaneous D-parity violation

We study the baryogenesis via leptogenesis in a class of left-right symmetric models, in which $D$-parity is broken spontaneously. We first discuss the consequence of the spontaneous $D$-parity breaking on the neutrino masses. Than we study the lepton asymmetry in various cases, from the decay of right handed neutrino as well as the triplet Higgs, depending on their relative masses they acquire from the symmetry breaking pattern. The leptogenesis bound on their masses are discussed by taking into account the low energy neutrino oscillation data. It is shown that a TeV scale leptogenesis is viable if there are additional sources of CP violation like domain wall originating from the spontaneous $D$-parity violation.

hep-ph↗

arXiv2006

Leptogenesis and low energy CP phases with two heavy neutrinos

An attractive explanation for non-zero neutrino masses and small matter antimatter asymmetry of the present Universe lies in "leptogenesis". At present the {\it size} of the lepton asymmetry is precisely known, while the {\it sign} is not known yet. In this work we determine the sign of this asymmetry in the framework of two right handed neutrino models by relating the leptogenesis phase(s) with the low energy CP violating phases appearing in the leptonic mixing matrix. It is shown that the knowledge of low energy lepton number violating re-phasing invariants can indeed determine the sign of the present matter antimatter asymmetry of the Universe and hence indirectly probing the light physical neutrinos to be Majorana type.

hep-ph↗

arXiv2006

Baryogenesis via Leptogenesis in presence of cosmic strings

We study the effect on leptogenesis due to $B-L$ cosmic strings of a $U(1)_{B-L}$ extension of the Standard Model. The disappearance of closed loops of $B-L$ cosmic strings can produce heavy right handed neutrinos, $N_R$'s, whose CP-asymmetric decay in out-of-thermal equilibrium condition can give rise to a net lepton ($L$) asymmetry which is then converted, due to sphaleron transitions, to a Baryon ($B$) asymmetry. This is studied by using the relevant Boltzmann equations and including the effects of both thermal and string generated non-thermal $N_R$'s. We explore the parameter region spanned by the effective light neutrino mass parameter $\tilde{m}_1$, the mass $M_1$ of the lightest of the heavy right-handed neutrinos (or equivalently the Yukawa coupling $h_1$) and the scale of $B-L$ symmetry breaking, $η_{B-L}$, and show that there exist ranges of values of these parameters, in particular with $η_{B-L} > 10^{11}\gev$ and $h_1\gsim 0.01$, for which the cosmic string generated non-thermal $N_R$'s can give the dominant contribution to, and indeed produce, the observed Baryon Asymmetry of the Universe when the purely thermal leptogenesis mechanism is not sufficient. We also discuss how, depending on the values of $η_{B-L}$, $\tilde{m}_1$ and $h_1$, our results lead to upper bounds on $\sinδ$, where $δ$ is the the CP violating phase that determines the CP asymmetry in the decay of the heavy right handed neutrino responsible for generating the $L$-asymmetry.

hep-ph↗

arXiv2006

Leptogenesis Below the Davidson-Ibarra Bound

The observed baryon asymmetry of the Universe is suitably created in thermal leptogenesis through the out-of-equilibrium decay of $N_1$, the lightest of the three heavy singlet neutral fermions which anchor the seesaw mechanism to obtain small Majorana neutrino masses. However, this scenario suffers from the incompatibility of a generic lower bound on the mass of $N_1$ and the upper bound on the reheating temperature of the Universe after inflation. A modest resolution of this conundrum is proposed.

hep-ph↗

arXiv2006

Dark matter and leptogenesis in gauged B-L symmetric models embedding $ν$ MSM

We study the phenomenon of baryogenesis via leptogenesis in the gauged $B-L$ symmetric models by embedding the currently proposed model $νMSM$. It is shown that the lightest right handed neutrino of mass $100 GeV$ satisfy the leptogenesis constraint and at the same time representing a candidate for the cold dark matter. We discuss our results in parallel to the predictions of $νMSM$.

hep-ph↗

arXiv2006

Bounds on neutrino masses from baryogenesis in thermal and non-thermal scenarios

Baryogenesis via leptogenesis is an attractive scenario that links the physics of right handed neutrino sector with the low energy neutrino data. In the light of current neutrino oscillation data we studied the bound on the mass scale ($M_1$) of lightest right handed neutrino ($N_1$) as well as their mass hierarchy ($M_2/M_1$ and $M_3/M_1$) from the leptogenesis constraint which we discussed in two different parts of the thesis. In part-I, we studied the canonical leptogenesis in a {\it thermal} scenario and hence the bound on $M_1$. It is shown that the mass scale of $N_1$ must satisfy the constraint $M_1\geq 10^8$ GeV in order to produce the adequate lepton asymmetry. We then led to propose a model where this bound can be relaxed to TeV scale. In part-II, we studied the formation and evolution of topological defects which are non-thermal objects and are expected to be formed during the early Universe phase transitions. In particular, we considered $B-L$ cosmic strings and their effect on leptogenesis and hence the bound on the mass scale of $N_1$. It is shown that for the $B-L$ symmetry breaking scale $η_{B-L}>10^{11}$GeV, in certain parameter space, the cosmic strings make a more dominant contribution than thermal leptogenesis.

hep-ph↗

arXiv2005

Heavy neutrino mass hierarchy from leptogenesis in left-right symmetric models with spontaneous CP-violation

We consider left-right symmetric model with spontaneous CP-violation. The Lagrangian of this model is CP invariant and the Yukawa couplings are real. Due to spontaneous breaking of the gauge symmetry, some of the neutral Higgses acquire complex vacuum expectation values, which lead to CP-violation. In the model considered here, we identify the neutrino Dirac mass matrix with that of Fritzsch type charged lepton mass matrix. We assume a hierarchical spectrum of the right handed neutrino masses and derive a bound on this hierarchy by assuming that the decay of the lightest right handed neutrino produces the baryon asymmetry via the leptogenesis route. It is shown that the mass hierarchy we obtain is compatible with the current neutrino oscillation data.

hep-ph↗

arXiv2005

Bounds on neutrino masses from leptogenesis in type-II see-saw models

The presence of the triplet $Δ_{L}$ in left-right symmetric theories leads to type-II see-saw mechanism for the neutrino masses. In these models, assuming a normal mass hierarchy for the heavy Majorana neutrinos, we derive a lower bound on the mass of the lightest of heavy Majorana neutrino from the leptogenesis constraint. From this bound we establish a consistent picture for the hierarchy of heavy Majorana neutrinos in a class of left right symmetric models in which we identify the neutrino Dirac mass matrix with that of Fritzsch type charged lepton mass matrix. It is shown that these values are compatible with the current neutrino oscillation data.

hep-ph↗

arXiv2005

Gauged $B-L$ symmetry and baryogenesis via leptogenesis at TeV scale

It is shown that the requirement of preservation of baryon asymmetry does not rule out a scale for leptogenesis as low as 10 TeV. The conclusions are compatible with see-saw mechanism if for example the pivot mass scale for neutrinos is $\approx 10^{-2}$ that of the charged leptons. We explore the parameter space $\tilde{m}_1$-$M_1$ of relevant light and heavy neutrino masses by solving Boltzmann equations. A viable scenario for obtaining baryogenesis in this way is presented in the context of gauged $B-L$ symmetry.

hep-ph↗

arXiv2004

B-L Cosmic strings and Baryogenesis

Cosmic strings arising from breaking of the $U(1)_{B-L}$ gauge symmetry that occurs in a wide variety of unified models can carry zero modes of heavy Majorana neutrinos. Decaying and/or repeatedly self-interacting closed loops of these ``$B-L$'' cosmic strings can be a non-thermal source of heavy right-handed Majorana neutrinos whose decay can contribute to the observed baryon asymmetry of the Universe (BAU) via the leptogenesis route. The $B-L$ cosmic strings are expected in GUT models such as SO(10), where they can be formed at an intermediate stage of symmetry breaking well below the GUT scale $\sim 10^{16}$ GeV; such light strings are not excluded by the CMB anisotropy data and may well exist. We estimate the contribution of $B-L$ cosmic string loops to the baryon-to-photon ratio of the Universe in the light of current knowledge on neutrino masses and mixings implied by atmospheric and solar neutrino measurements. We find that $B-L$ cosmic string loops can contribute significantly to the BAU for $U(1)_{B-L}$ symmetry breaking scale $η_{B-L}\gsim 1.7\times 10^{11}\gev$. At the same time, in order for the contribution of decaying $B-L$ cosmic string loops not to exceed the observed baryon-to-photon ratio inferred from the recent WMAP results, the lightest heavy right-handed Majorana neutrino mass $M_1$ must satisfy the constraint $M_1 \leq 2.4 \times 10^{12}(η_{B-L}/10^{13}\gev)^{1/2}\gev$. This may have interesting implications for the associated Yukawa couplings in the heavy neutrino sector and consequently for the light neutrino masses generated through see-saw mechanism.

hep-ph↗