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Utpal Sarkar

Publications and source records attributed to Utpal Sarkar.

At least 91 records · Page 5Linked to original sources
arXiv2006

CP violation in neutrino mass matrix

We constructed rephasing invariant measures of CP violation with elements of the neutrino mass matrix, in the basis in which the charged lepton mass matrix is diagonal. We discuss some examples of neutrino mass matrices with texture zeroes, where the present approach is applicable and demonstrate how it simplifies an analysis of CP violation. We applied our approach to study CP violation in all the phenomenologically acceptable 3-generation two-zero texture neutrino mass matrices and shown that in any of these cases there is only one CP phase which contributes to the neutrino oscillation experiment and there are no Majorana phases.

hep-ph↗
arXiv2006

Anomaly for Model Building

A simple algorithm to calculate the group theory factor entering in anomalies at four and six dimensions for SU(N) and SO(N) groups in terms of the Casimir invariants of their subgroups is presented. Explicit examples of some of the lower dimensional representations of $SU(n), n \leq 5$ and SO(10) groups are presented, which could be used for model building in four and six dimensions.

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arXiv2006

See-saw fermion masses in an SO(10) GUT

In this work we study an SO(10) GUT model with minimum Higgs representations belonging only to the 210 and 16 dimensional representations of SO(10). We add a singlet fermion S in addition to the usual 16 dimensional representation containing quarks and leptons. There are no Higgs bi-doublets and so charged fermion masses come from one-loop corrections. Consequently all the fermion masses, Dirac and Majorana, are of the see-saw type. We minimize the Higgs potential and show how the left-right symmetry is broken in our model where it is assumed that a D-parity odd Higgs field gets a vacuum expectation value at the grand unification scale. From the renormalization group equations we infer that in our model unification happens at 10^{15} GeV and left-right symmetry can be extended up to some values just above 10^{11} GeV. The Yukawa sector of our model is completely different from most of the standard grand unified theories and we explicitly show how the Yukawa sector will look like in the different phases and briefly comment on the running of the top quark mass. We end with a brief analysis of lepton number asymmetry generated from the interactions in our model.

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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.

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arXiv2006

Connecting Dark Energy to Neutrinos with an Observable Higgs Triplet

To connect the scalar field (acceleron) responsible for dark energy to neutrinos, the usual strategy is to add unnaturally light neutral singlet fermions (right-handed neutrinos) to the Standard Model. A better choice is actually a Higgs triplet, through the coupling of the acceleron to the trilinear Higgs triplet-double-doublet interaction. This hypothesis predicts an easily observable doubly-charged Higgs boson at the forthcoming Large Hadron Collider (LHC).

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arXiv2005

Split Supersymmetry in an Orbifold GUT

We propose a supersymmetric SU(5) orbifold GUT in 5 dimensions in which supersymmetry breaking at the boundaries give rise to split supersymmetry spectrum. The extra dimension is compactified on a $S^1/Z_2 \times Z_2^\prime$ orbifold having two fixed points. The standard model fermions are localized in the standard model brane, where supersymmetry is broken by the nonvanishing of the F-term of a superfield X at some intermediate scale. All scalar superpartners acquires mass at this stage. The standard model gauginos and higgsinos remain light, since their masses are protected by R-symmetry and induced only by loop contributions and contact interaction in our brane. Usual features of orbifold GUTs are preserved in this scenario and proton decay and neutrino mass problems are solved.

hep-ph↗
arXiv2004

An SO(10) GUT With See-Saw Masses For All Fermions

We propose an SO(10) grand unified theory which has the simplest Higgs structure discussed so far in the literature. We include only two Higgs scalars, a 210-plet and a 16-plet. In addition to the regular fermions we include one singlet, whose mass term breaks chiral symmetry, so that fermions can get masses. All fermions acquire see-saw masses, since there are no Higgs bi-doublets. Required neutrino masses with large mixing as well as leptogenesis are possible in this model.

hep-ph↗
arXiv2004

Minimal supersymmetric SO(10) GUT with doublet Higgs

We propose a simple supersymmetric SO(10) GUT model with only doublet Higgs scalars. The fermion mass problem is naturally solved by a new one-loop diagram. R-parity is conserved implying a stable LSP which can explain the dark matter of the universe. There are two contributions to the neutrino masses, one of which depends on the quark mass squared while the other is independent and similar to the type II see-saw mechanism. In the latter case $b-τ$ unification implies large neutrino mixing angles. The baryon asymmetry of the universe is explained through leptogenesis.

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arXiv2004

Parity in left-right symmetric models

We considered parity breaking in some left-right symmetric models. We studied spontaneous and explicit parity violation in two cases with doublet and triplet Higgs scalars. The minimization condition in these two cases differ significantly. A comparative study of these models is presented emphasizing their phenomenological consequences.

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arXiv2003

Truly Minimal Left-Right Model of Quark and Lepton Masses

We propose a left-right model of quarks and leptons based on the gauge group $SU(3)_C \times SU(2)_L \times SU(2)_R \times U(1)_{B-L}$, where the scalar sector consists of only two doublets: (1,2,1,1) and (1,1,2,1). As a result, any fermion mass, whether it be Majorana or Dirac, must come from dimension-five operators. This allows us to have a common view of quark and lepton masses, including the smallness of Majorana neutrino masses as the consequence of a double seesaw mechanism.

hep-ph↗
arXiv2003

Gauged B-3L_τ, low-energy unification and proton decay

We point out that if there is a gauged $B-3L_τ$ symmetry at low energy, it can prevent fast proton decay. This may help building models with theories with extra dimensions at the TeV scale. For purpose of illustration we present an explicit model with large extra dimensions. The Higgs required for a realistic fermion masses and mixing are included. The problem of neutrino masses are solved with triplet Higgs scalars. The proton remains stable even after the $B-3L_τ$ symmetry breaking.

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arXiv2001

Neutrino Mass Matrices in Models with Horizontal Symmetries

We have studied the most general neutrino mass matrices in models with SU(2) and SU(3) horizontal symmetries. Without going into the details of the models it is possible to write down the effective operators, which predict the structure of the Majorana neutrino mass matrices. Unlike other extensions of the standard model, the structure is now independent of the effective Yukawa couplings and depends entirely on the Higgs which gives mass to the other fermions. In the case of SU(3) symmetries the lowest dimensional operators are forbidden requiring a low mass scale for lepton number violation.

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arXiv2001

Supersymmetric Model of Neutrino Mass and Leptogenesis with String-Scale Unification

Adjoint supermultiplets (1,3,0) and (8,1,0) modify the evolution of gauge couplings. If the unification of gauge couplings occurs at the string scale, their masses are fixed at around $10^{13}$ GeV. This scale coincides with expected gaugino condensation scale in the hidden sector $M_{string}^{2/3} m^{1/3}_{3/2} \sim 10^{13}$ GeV. We show how neutrino masses arise in this unified model which naturally explain the present atmospheric and solar neutrino data. The out-of-equilibrium decay of the superfield (1,3,0) at $10^{13}$ GeV may also lead to a lepton asymmetry which then gets converted into the present observed baryon asymmetry of the Universe.

hep-ph↗
arXiv2001

Phenomenology of the Neutrino-Mass-Giving Higgs Triplet and the Low-Energy Seesaw Violation of Lepton Number

Small realistic Majorana neutrino masses can be generated via a Higgs triplet $(ξ^{++}, ξ^+, ξ^0)$ without having energy scales larger than $M_*={\cal O}(1)$ TeV in the theory. The large effective mass scale $Λ$ in the well-known seesaw neutrino-mass operator $Λ^{-1} (LLΦΦ)$ is naturally obtained with $Λ\sim M_*^2/μ,$ where $μ$ is a {\it small} scale of lepton-number violation. In theories with large extra dimensions, the smallness of $μ$ is naturally obtained by the mechanism of ``shining'' if the number of extra dimensions $n\ge 3.$ We study here the Higgs phenomenology of this model, where the spontaneous violation of lepton number is treated as an external source from extra dimensions. The observable decays $ξ^{++} \to l_i^+l_j^+$ will determine directly the magnitudes of the $\{ij\}$ elements of the neutrino mass matrix. The decays $ξ^+ \to W^+ J^0$ and $ξ^0 \to Z J^0$, where $J^0$ is the massless Goldstone boson (Majoron), are also possible, but of special importance is the decay $ξ^0 \to J^0 J^0$ which provides stringent constraints on the allowed parameter space of this model. Based on the current neutrino data, we also predict observable rates of $μ-e$ conversion in nuclei.

hep-ph↗
arXiv2001

New Dimensions New Hopes

We live in a four dimensional world. But the idea of unification of fundamental interactions lead us to higher dimensional theories. Recently a new theory with extra dimensions has emerged, where only gravity propagates in the extra dimension and all other interactions are confined in only four dimensions. This theory gives us many new hopes. In earlier theories unification of strong, weak and the electromagnetic forces was possible at around (10^{16}) GeV in a grand unified theory (GUT) and it could get unified with gravity at around the Planck scale of (10^{19}) GeV. With this new idea it is possible to bring down all unification scales within the reach of the next generation accelerators, i.e., around $10^4$ GeV.

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arXiv2000

Allowable Low-Energy E_6 Subgroups from Leptogenesis

There are only two viable low-energy $E_6$ subgroups: $SU(3)_C \times SU(2)_L \times U(1)_Y \times U(1)_N$ or $SU(3)_C \times SU(2)_L \times SU(2)'_R \times U(1)_{Y_L + Y'_R}$, which would not erase any preexisting lepton asymmetry of the Universe that may have been created by the decay of heavy singlet (right-handed) neutrinos or any other mechanism. They are also the two most favored $E_6$ subgroups from a recent analysis of present neutral-current data. We study details of the leptogenesis, as well as some salient experimental signatures of the two models.

hep-ph↗
arXiv2000

Possible textures of neutrino and charged lepton mass matrices

We study a variety of different texture patterns in the basis in which the charged lepton mass matrix or neutrino mass matrix or neither are diagonal. The experimental results on the neutrinos provide sufficient restrictions to allow only a small number of simple patterns. We discuss particularly the texture zeroes which provide important relations among the mass eigenvalues and the mixing matrix.

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