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Utpal Sarkar

Publications and source records attributed to Utpal Sarkar.

At least 127 records · Page 7Linked to original sources
arXiv1998

Baryogenesis through lepton number violation

The most promising scenarios of baryogenesis seems to be the one through lepton number violation. Lepton number violation through a Majarana mass of the right-handed neutrinos can generate a lepton asymmetry of the universe when the right-handed neutrinos decay. The left-handed neutrinos get small Majorana masses through see-saw mechanism in these models. A triplet higgs scalar violating lepton number explicitly through its couplings to two leptons or two higgs doublets can also naturally give small Majorana masses to the left-handed neutrinos and also generate a lepton asymmetry of the universe. We review both these models of leptogenesis, where the lepton number asymmetry then gets converted to a baryon asymmetry of the universe before the electroweak phase transition.

hep-ph↗
arXiv1998

Electroweak Baryon Number Violation and Constraints on Left-handed Majorana Neutrino Masses

During a large period of time, the anomalous baryon number violating interactions are in equilibrium, when the $(B+L)$ asymmetry is washed out. If there is any lepton number violation during this period, that will also erase the $(B-L)$ asymmetry. As a result, survival of the baryon asymmetry of the universe pose strong constraints on lepton number violating interactions. We review here the constraints on the left-handed Majorana neutrino masses arising from this survival requirement of the baryon asymmetry of the universe. We then briefly review models of leptogenesis, where lepton number violation is used to generate a baryon asymmetry of the universe and hence the constraints on the Majorana neutrino mass is relaxed.

hep-ph↗
arXiv1998

Degenerate Dirac Neutrinos

A simple extension of the standard model is proposed in which all the three generations of neutrinos are Dirac particles and are naturally light. We then assume that the neutrino mass matrix is diagonal and degenerate, with a few eV mass to solve the dark matter problem. The self energy radiative corrections, however, remove this degeneracy and allow mixing of these neutrinos. The electroweak radiative corrections then predict a lower bound on the $ν_μ- ν_e$ mass difference which solves the solar neutrino problem through MSW mechanism and also predict a lower bound on the $ν_τ- ν_μ$ mass difference which is just enough to explain the atmospheric neutrino problem as reported by super Kamiokande.

hep-ph↗
arXiv1998

Naturally light sterile neutrinos

A simple model to accomodate light sterile neutrinos naturally with large mixing with the usual neutrinos has been proposed. The standard model gauge group is extended to include an $SU(2)_S$ gauge symmetry. Heavy triplet higgs scalars give small masses to the left-handed neutrinos, while a heavy doublet higgs scalar give mixing with the sterile neutrinos of the same order of magnitude. The neutrino mass matrix thus obtained can explain the solar neutrino deficit, the atmospheric neutrino deficit, the LSND data and hot dark matter. Lepton number is violated here through decays of the heavy triplet higgs, which generates the lepton asymmetry of the universe, which in turn generates a baryon asymmetry of the universe.

hep-ph↗
arXiv1998

Gauged $B - 3 L_τ$ and Baryogenesis

It has recently been shown that by extending the minimal standard model to include a right-handed partner to $ν_τ$, it is possible to gauge the $B - 3 L_τ$ quantum number consistently. If we add two scalar triplets, one trivial ($ξ_1$) and one nontrivial ($ξ_2$) under $B - 3 L_τ$, it is possible also to have desirable neutrino masses and mixing for neutrino oscillations. At the same time, a lepton asymmetry can be generated in the early universe through the novel mechanism of the decay of the heavier $ξ_1$ into the lighter $ξ_2$ plus a neutral singlet ($ζ^0$). This lepton asymmetry then gets converted into a baryon asymmetry at the electroweak phase transition.

hep-ph↗
arXiv1998

Neutrino Masses and Leptogenesis with Heavy Higgs Triplets

A simple and economical extension of the minimal standard electroweak gauge model (without right-handed neutrinos) by the addition of two heavy Higgs scalar triplets would have two significant advantages. \underline {Naturally} small Majorana neutrino masses would become possible, as well as leptogenesis in the early universe which gets converted at the electroweak phase transition into the present observed baryon asymmetry.

hep-ph↗
arXiv1998

Scale of Leptogenesis

We study the scale at which one can generate the lepton asymmetry of the universe which could then get converted to a baryon asymmetry during the electroweak phase transition. We consider the possibility that the Yukawa couplings are small but sufficiently large to generate enough lepton asymmetry. This forbids the possibility of the $(B-L)$ breaking scale being the electroweak scale.

hep-ph↗
arXiv1998

Constraints on background torsion field from K physics

We point out that a background torsion field will produce an effective potential to the $K$ and $\bar{K}$ with opposite signs. This allows us to constrain the background torsion field from the $K_L$ and $K_S$ mass difference, CPT violating $K^\circ$ and $\bar{K^\circ}$ mass difference and the CP violating quantities $ε$ and $η_{+-}$. The most stringent bound on the cosmological background torsion $< T^0 > < 10^{-25}$ GeV comes from the direct measurement of the CPT violation.

hep-ph↗
arXiv1996

Baryogenesis in a supersymmetric model without R-parity

We propose a simple scenario for baryogenesis in supersymmetric models where baryon number is broken alongwith R-parity. The lightest supersymmetric particle (neutralino) decays to three quarks and $CP-$ violation comes from interference of tree and one loop box diagrams. The bounds on the $R-$parity breaking couplings from the out-of-equilibrium condition are considerably relaxed in this scenario.

hep-ph↗
arXiv1996

Spontaneous Leptogenesis

I propose a new mechanism for baryogenesis, in which the out-of-equilibrium condition is not neccessary. When the electroweak symmetry is broken spontaneously, left-handed neutrinos may get Majorana masses containing $CP-$violating phases. This induces a lepton asymmetry spontaneously, which is then converted to a baryon asymmetry in the presence of the sphaleron field.

hep-ph↗
arXiv1996

Baryogenesis through R-parity violation

We consider generation of baryon asymmetry of the universe through $R-$parity violation in a scenario in which out-of-equilibrium condition is satisfied by making the electroweak phase transition to be first order. We study all the $R-$parity violating interaction which can generate $(B-L)$ asymmetry which then converts to baryon asymmetry of the universe. We demonstrate that CP--violating sfermion deudy all the $R-$parity violating interaction which can generate $(B-L)$ asymmetry which then converts to baryon asymmetry of the universe. We demonstrate that CP--violating sfermion decays contribute more than that of the neutralino decays in the generation of $(B-L)$ asymmetry.

hep-ph↗
arXiv1996

Baryogenesis Through Mixing of Heavy Majorana Neutrinos

A mechanism is presented, in which the mixing of right handed heavy Majorana neutrinos creates a $CP-$asymmetric universe. When these Majorana neutrinos subsequently decay more leptons than anti-leptons are produced. The lepton asymmetry created by this new mechanism can exceed by a few orders of magnitude any lepton asymmetry originating from direct decays. The asymmetry is finally converted into a baryon asymmetry during the electroweak phase transition.

hep-ph↗
arXiv1996

Electroweak Baryogenesis and Constraints on Left-handed Majorana Neutrino Masses

The lepton number violating interactions generated by the light Majorana neutrinos can erase the primordial baryon asymmetry of the universe during the electroweak phase transition. The Majorana masses of the left-handed neutrinos are constrained to avoid this problem. These constraints do not depend on the $(B-L)$ symmetry breaking mechanism.

hep-ph↗
arXiv1995

Baryon and Lepton Number Assignment in $E_6$ Models

In $E_6$ models there are new particles whose baryon number is not uniquely assigned. We point out that the baryon and lepton number assignment to these particles can change the baryogenesis scenario significantly. We consider left-right symmetric extension of the standard model in which $(B-L)$ quantum number is gauged. The identification of $(B-L)$ with a generator of $E_6$ is used to define the baryon and lepton numbers for the exotic particles in a way that the electroweak baryon and lepton number anomaly corresponding to the $SU(2)_L$ group vanishes, {\it i.e.}, there is no non-perturbative baryon or lepton number violation during the electroweak phase transition. We study some consequences of the new assignment.

hep-ph↗
arXiv1995

A Model for the Three Lepton Decay Mode of the Proton

An extension of the left--right symmetric model has been constructed which gives in a natural way the three lepton decay modes of the proton which have been suggested as an explanation for the atmospheric neutrino anomaly. We write down the potential which after minimization gives the proper choice of the Higgs spectrum. With this Higgs spectrum we then study the evolution of the gauge coupling constants and point out that for consistency one has to include effects of gravity.

hep-ph↗
arXiv1994

Baryogenesis from a Lepton Asymmetric Universe

We demonstrate that $CP-$violation in the Majorana mass matrices of the heavy neutrinos can generate a $CP-$asymmetric universe. The subsequent decay of the Majorana particles generates a lepton number asymmetry. During the electroweak phase transition the lepton asymmetry is converted into a baryon asymmetry, which survives down to this time.

hep-ph↗
arXiv1994

Low Energy Leptogenesis in Left-Right Symmetric Models

We propose a new mechanism for baryogenesis. We study the effective potential of left-right extension of the standard model and show that there can be a first order phase transition at the left-right symmetry breaking and hence $(B-L)$ symmetry breaking scale, which is around TeV in our scenario. As a result, although $(B-L)$ violating interactions are in equilibrium at this scale, enough $(B-L)$ asymmetry may be generated. This $(B-L)$ asymmetry is then converted to baryon asymmetry during the anomalous electroweak process. If right handed gauge bosons are seen in the TeV scale, then we argue that this will be the only consistent mechanism to generate baryon asymmetry of the universe.

hep-ph↗