arXiv subjects

Utpal Sarkar

Publications and source records attributed to Utpal Sarkar.

At least 109 records · Page 6Linked to original sources

arXiv2000

Low-Scale Axion from Large Extra Dimensions

The mass of the axion and its decay rate are known to depend only on the scale of Peccei-Quinn symmetry breaking, which is constrained by astrophysics and cosmology to be between $10^9$ and $10^{12}$ GeV. We propose a new mechanism such that this effective scale is preserved and yet the fundamental breaking scale of $U(1)_{PQ}$ is very small (a kind of inverse seesaw) in the context of large extra dimensions with an anomalous U(1) gauge symmetry in our brane. Unlike any other (invisible) axion model, there are now possible collider signatures in this scenario.

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arXiv2000

Light Sterile Neutrinos from Large Extra Dimensions

An experimentally verifiable Higgs-triplet model of neutrino masses from large extra dimensions was recently proposed. We extend it to accomodate a light sterile neutrino which also mixes with the three active neutrinos. A previously proposed phenomenological model of four neutrinos (\underline {the only viable such model now left}, in view of the latest atmospheric and solar neutrino-oscillation data) is specifically realized.

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arXiv2000

Leptogenesis from Neutralino Decay with Nonholomorphic R-Parity Violation

In supersymmetric models with lepton-number violation, hence also R-parity violation, it is easy to have realistic neutrino masses, but then leptogenesis becomes difficult to achieve. After explaining the general problems involved, we study the details of a model which escapes these constraints and generates a lepton asymmetry, which gets converted into the present observed baryon asymmetry of the Universe through the electroweak sphalerons. This model requires the presence of certain nonholomorphic R-parity violating terms. For completeness we also present the most general R-parity violating Lagrangian with soft nonholomorphic terms and study their consequences for the charged-scalar mass matrix. New contributions to neutrino masses in this scenario are discussed.

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arXiv2000

Verifiable Model of Neutrino Masses from Large Extra Dimensions

We propose a new scenario of neutrino masses with a Higgs triplet $(ξ^{++},ξ^+,ξ^0)$ in a theory of large extra dimensions. Lepton number violation in a distant brane acts as the source of a very small trilinear coupling of $ξ$ to the standard Higgs doublet in our brane. Small realistic Majorana neutrino masses are \underline{naturally} obtained with the fundamental scale $M_* \sim {\cal O}(1)$ TeV, foretelling the possible discovery of $ξ$ $(m_ξ\lsim M_*)$ at future colliders. Decays of $ξ^{++}$ into same-sign dileptons are fixed by the neutrino mass matrix. Observation of $μ-e$ conversion in nuclei is predicted.

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arXiv2000

Neutrino Masses and the Gluino Axion Model

We extend the recently proposed gluino axion model to include neutrino masses. We discuss how the canonical seesaw model and the Higgs triplet model may be realized in this framework. In the former case, the heavy singlet neutrinos are contained in superfields which do not have any vacuum expectation value, whereas the gluino axion is contained in one which does. We also construct a specific renormalizable model which realizes the mass scale relationship $M_{SUSY} \sim f_a^2/M_U$, where $f_a$ is the axion decay constant and $M_U$ is a large effective mass parameter.

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arXiv2000

About the Mixing and CP Violation in Neutrino System

Suppose the geometrical explaination to the weak CP phase in quark sector is also valid for neutrinos, the mixing and CP violation in neutrino system are discussed. We find a larger $J_{CP}$ than $3\times 10^{-3}$ implys the large-mixing solution for solar neutrino problem. In case of bi-maximal mixing, we predict relative large CP violation with $J_{CP}$ larger than $10^{-3}$ in neutrino system, except the third mixing angle approachs to 0 or $π/2$ very closely.

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arXiv1999

Leptogenesis from R parity nonconservation

It is known that realistic neutrino masses for neutrino oscillations may be obtained from R parity nonconserving supersymmetry. It is also known that such interactions would erase any preexisting lepton or baryon asymmetry of the Universe because of the inevitable intervention of the electroweak sphalerons. We now show how a crucial subset of these R parity nonconserving terms may in fact create its own successful leptogenesis.

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arXiv1999

Lepton flavor mixing and baryogenesis

Recently a new general class of quark mass matrix ansatz has been proposed, which originates from some flavor symmetry. We extend that symmetry to the lepton sector and study the neutrino mass matrix and address the question of the baryon asymmetry of the universe in this model.

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arXiv1999

Models of Neutrino Masses and Baryogenesis

Majorana masses of the neutrino implies lepton number violation and is intimately related to the lepton asymmetry of the universe, which gets related to the baryon asymmetry of the universe in the presence of the sphalerons during the electroweak phase transition. Assuming that the baryon asymmetry of the universe is generated before the electroweak phase transition, it is possible to dicriminate different classes of models of neutrino masses. While see-saw mechanism and the triplet higgs mechanism are preferred, the Zee-type radiative models and the R-parity breaking models requires additional inputs to generate baryon asymmetry of the universe during the electroweak phase transition.

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arXiv1999

CP violation in neutrino mixing matrix and leptogenesis

The CP violation required in leptogenesis may have different origin, but in an effective theory they all are related to the rephasing invariant CP violating measure in the mixing matrix of the leptonic sector. We point out that the maximum amount of CP violation in some models can be estimated with our present knowledge of the neutrino mixing angles, which can help us understand the CP violation in the generation of the lepton asymmetry of the universe. For example, the possibility of leptogenesis may be ruled out in some models from an knowledge of the effective neutrino mass matrix.

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arXiv1999

Scale of SU(2)_R symmetry breaking and leptogenesis

Models of leptogenesis often invoke the out-of-equilibrium decays of heavy right-handed neutrinos in order to create a baryon asymmetry of the universe through the electroweak phase transition. Their presumed existence argues strongly for the presence of an $SU(2)_R$ gauge symmetry. We study the equilibrating effects of the resulting additional right-handed interactions and find that successful leptogenesis requires that $m_N \gtrsim 10^{16}$ GeV if $m_N > m_{W_R}$, and $m_{W_R} \gtrsim 3 \times 10^6 GeV (m_N /10^2 GeV)^{2/3}$ if $m_{N} m_{W_R}$ option is excluded in a supersymmetric theory with gravitinos.

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arXiv1999

Neutrino Masses in Supersymmetry: R-Parity and Leptogenesis

In the supersymmetric standard model of particle interactions, R-parity nonconservation is often invoked to obtain nonzero neutrino masses. We point out here that such interactions of the supersymmetric particles would erase any pre-existing lepton or baryon asymmetry of the universe before the electroweak phase transition through the $B + L$ violating sphaleron processes. We then show how neutrino masses may be obtained in supersymmetry (assuming R-parity conservation) together with successful leptogenesis and predict the possible existence of new observable particles.

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arXiv1998

Gravitino constraints on models of neutrino masses and leptogenesis

In the supersymmetric extensions of the standard model, neutrino masses and leptogenesis requires existence of new particles. We point out that if these particles with lepton number violating interactions have standard model gauge interactions, then they may not be created after reheating because of the gravitino problem. This will rule out all existing models of neutrino masses and leptogenesis, except the one with right-handed singlet neutrinos.

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arXiv1998

A See-Saw Model for Atmospheric and Solar Neutrino Oscillations

We have constructed an explicit see-saw model containing two singlet neutrinos, one carrying a $(B-3L_e)$ gauge charge with an intermediate mass scale of $\sim O(10^{10})$ GeV along with a sterile one near the GUT (grand unification theory) scale of $\sim O(10^{16})$ GeV. With these mass scales and a reasonable range of Yukawa couplings, the model can naturally account for the near-maximal mixing of atmospheric neutrino oscillations and the small mixing matter-enhanced oscillation solution to the solar neutrino deficit.

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arXiv1998

Texture of a Four-Neutrino Mass Matrix

We propose a simple texture of the neutrino mass matrix with one sterile neutrino along with the three standard ones. It gives maximal mixing angles for $ν_e \to ν_S$ and $ν_μ\to ν_τ$ oscillations or vice versa. Thus with only four parameters, this mass matrix can explain the solar neutrino anomaly, atmospheric neutrino anomaly, LSND result and the hot dark matter of the universe, while satisfying all other Laboratory constraints. Depending on the choice of parameters, one can get the vacuum oscillation or the large angle MSW solution of the solar neutrino anomaly.

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arXiv1998

Baryogenesis with Scalar Bilinears

We show that if a baryon asymmetry of the universe is generated through the out-of-equilibrium decays of heavy scalar bilinears coupling to two fermions of the minimal standard model, it is necessarily an asymmetry conserving $(B-L)$ which cannot survive past the electroweak phase transition because of sphalerons. We then show that a surviving $(B-L)$ asymmetry may be generated if the heavy scalars decay into two fermions, \underline {and into two light scalars} (which may be detectable at hadron colliders). We list all possible such trilinear scalar interactions, and discuss how our new baryogenesis scenario may occur naturally in supersymmetric grand unified theories.

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arXiv1998

Probing the Exotic Particle Content Beyond the Standard Model

We explore the possible exotic particle content beyond the standard model by examining all its scalar bilinear combinations. We categorize these exotic scalar fields and show that without the suppression of (A) their Yukawa couplings with the known quarks and leptons, and (B) the trilinear couplings among themselves, most are already constrained to be very heavy from the nonobservation of proton decay and neutron-antineutron oscillations, the smallness of $K^0 - \bar {K^0}$, $D^0 - \bar {D^0}$ and $B_d^0 - \bar {B_d^0}$ mixing, as well as the requirement of a nonzero baryon asymmetry of the universe. On the other hand, assumption (B) may be naturally violated in many models, especially in supersymmetry, hence certain exotic scalars are allowed to be below a few TeV in mass and would be easily detectable at planned future hadron colliders. In particular, large cross sections for the distinctive processes like $\bar p p \to tt,\bar t c$ and $p p \to t t, b b$ would be expected at the Fermilab Tevatron and CERN LHC, respectively.

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arXiv1998

CP violation in the mass matrix of heavy neutrinos

We discuss the question of CP-violation in the effective Hamiltonian approach in models of leptogenesis through heavy right handed neutrino decays. We first formulate the problem in four component notation and then point out that before the heavy neutrinos have decayed away, the universe becomes CP-asymmetric in the heavy neutrinos. However, the lepton asymmetry generated after they completely decay are independent of this asymmetry.

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