arXiv subjects

K. T. Mahanthappa

Publications and source records attributed to K. T. Mahanthappa.

36 records · Page 2Linked to original sources

arXiv2004

Fermion Masses and Neutrino Oscillations in SO(10) x SU(2)_{F}

We present in this talk a model based on SO(10) x SU(2)_{F} having symmetric mass textures with 5 zeros constructed by us recently. The symmetric mass textures arising from the left-right symmetry breaking chain of SO(10) give rise to good predictions for the masses, mixing angles and CP violation measures in the quark and lepton sectors (including the neutrinos), all in agreement with the most up-to-date experimental data within 1 sigma. Various lepton flavor violating decays in our model are also investigated. Unlike in models with lop-sided textures, our prediction for the decay rate of mu -> e gamma is much suppressed and yet it is large enough to be probed by the next generation of experiments. The observed baryonic asymmetry in the Universe can be accommodated in our model utilizing soft leptogenesis.

hep-ph↗

arXiv2003

An Overview of Neutrino Masses and Mixing in SO(10) Models

We review in this talk various SUSY SO(10) models. Specifically, we discuss how small neutrino masses are generated in and generic predictions of different SO(10) models. A comparison of the predictions of these models for sin^{2}(theta_{13}) is given.

hep-ph↗

arXiv2003

Symmetric Textures in SO(10) and LMA Solution for Solar Neutrinos

A model based on SUSY SO(10) combined with SU(2) family symmetry is constructed. In contrast with the commonly used effective operator approach, 126-dimensional Higgs fields are utilized to construct the Yukawa sector. R-parity symmetry is thus preserved at low energies. The symmetric mass textures arising from the left-right symmetry breaking chain of SO(10) give rise to very good predictions for quark and lepton masses and mixings. The prediction for sin(2beta) agrees with the average of current bounds from BaBar and Belle. In the neutrino sector, our predictions are in good agreement with results from atmospheric neutrino experiments. Our model accommodates the LMA solution to the solar neutrino anomaly. The prediction of our model for the |U(e nu_3)| element in the MNS matrix is close to the sensitivity of current experiments; thus the validity of our model can be tested in the near future. We also investigate the correlation between the |U(e nu_3)| element and tan^{2}(theta_odot) in a general two-zero neutrino mass texture.

hep-ph↗

arXiv2003

Fermion Masses and Mixing and CP-Violation in SO(10) Models with Family Symmetries

Several ideas for solving the problem of fermion mass hierarchy and mixing and specific supersymmetric models that realize it are reviewed. In particular, we discuss many models based on SO(10) in four dimensions combined with a family symmetry to accommodate fermion mass hierarchy and mixing, including the case of neutrinos. These models are compared and various tests that can be used to distinguish these models are suggested. We also include a discussion of a few SO(10) models in higher space-time dimensions.

hep-ph↗

arXiv2003

Symmetric Textures in SO(10) and LMA Solution for Solar Neutrinos

We analyze a model based on SUSY SO(10) combined with SU(2) family symmetry and symmetric mass matrices constructed by the authors recently. Previously, only the parameter space for the LOW and vacuum oscillation (VO) solutions was investigated. We indicate in this note the parameter space which leads to large mixing angle (LMA) solution to the solar neutrino problem with a slightly modified effective neutrino mass matrix. The symmetric mass textures arising from the left-right symmetry breaking and the SU(2) symmetry breaking give rise to very good predictions for the quark and lepton masses and mixing angles. The prediction of our model for the |U_{eν_{3}}| element in the Maki-Nakagawa-Sakata (MNS) matrix is close to the sensitivity of current experiments; thus the validity of our model can be tested in the near future. We also investigate the correlation between the |U_{eν_{3}}| element and \tan^{2}θ_{\odot} in a general two-zero neutrino mass texture.

hep-ph↗

arXiv2001

CP Violation in a Supersymmetric SO(10) x U(2)_{F} Model

A model based on SUSY SO(10) combined with U(2) family symmetry constructed recently by the authors is generalized to include phases in the mass matrices leading to CP violation. In contrast with the commonly used effective operator approach, $\bar{126}$-dimensional Higgs fields are utilized to construct the Yukawa sector. R-parity symmetry is thus preserved at low energies. The symmetric mass textures arising from the left-right symmetry breaking chain of SO(10) give rise to very good predictions for quark and lepton masses and mixings. The prediction for $\sin 2β$ agrees with the average of current bounds from BaBar and Belle. In the neutrino sector, our predictions are in good agreement with results from atmospheric neutrino experiments. Our model favors both the LOW and QVO solutions to the solar neutrino anomaly; the matrix element for neutrinoless double beta decay is highly suppressed. The leptonic analog of the Jarlskog invariant, $J_{CP}^{l}$, is predicted to be of $O(10^{-2})$.

hep-ph↗

arXiv2001

CP Violation in a SUSY SO(10) x U(2)_{F} Model

We construct a model based on SUSY SO(10) combined with U(2) family symmetry including complex phases leading to CP violation. In contrast with the commonly used effective operator approach, \bar{126}-dimensional Higgs fields are utilized to construct the Yukawa sector. R-parity symmetry is thus preserved at low energies. The symmetric mass textures arising from the left-right symmetry breaking chain of SO(10) give rise to very good predictions for quark and lepton masses and mixings. The prediction for \sin 2βagrees with the current bounds from BaBar and Belle. In the neutrino sector, our predictions are in good agreement with results from atmospheric neutrino experiments. Our model favors both the LOW and QVO solutions to the solar neutrino anomaly; the matrix element for neutrinoless double beta decay is highly suppressed. The leptonic analog of the Jarlskog invariant, J_{CP}^{l}, is predicted to be of O(10^{-2}).

hep-ph↗

arXiv2001

Implications of the Renormalization Group Equations in Three-Neutrino Models with Two-fold Degeneracy

We obtain a {\it complete set} of one-loop RGE's for a set of combinations of neutrino parameters for the case of two-fold degenerate hierarchical three-neutrino models. The requirement of consistency of exact solutions to these RGE's with the two-fold degeneracy yields conditions which have previously been obtained perturbatively/numerically. These conditions, in the limit $|U_{eν_{3}}|=0$, are shown to lead to a strong cancellation in the matrix element of neutrinoless double beta decay.

hep-ph↗

arXiv2000

Neutrino Mixing from the CKM matrix in SUSY SO(10) \times U(2)_{F}

We construct a realistic model based on SUSY SO(10) with U(2) flavor symmetry. A set of symmetric mass textures give rise to very good predictions; 15 masses and 6 mixing angles are predicted by 11 parameters. Both the vacuum oscillation and LOW solutions are favored for the solar neutrino problem.

hep-ph↗

arXiv2000

From CKM Matrix to MNS Matrix: A Model Based on Supersymmetric $SO(10) \times U(2)_{F}$ Symmetry

We construct a realistic model based on SUSY SO(10) with U(2) flavor symmetry. In contrast to the commonly used effective operator approach, $126-$dimensional Higgses are used to construct the Yukawa sector. R-parity symmetry is thus preserved at low energies. The Dirac and right-handed Majorana mass matrices in our model have very small mixing, and they combine with the seesaw mechanism resulting in a large leptonic mixing. The symmetric mass textures arising from the left-right symmetry breaking chain of SO(10) give rise to very good predictions; 15 masses (including 3 right-handed Majorana neutrino masses) and 6 mixing angles are predicted by 11 parameters. Both the vacuum oscillation and LOW solutions are favored for the solar neutrino problem.

hep-ph↗

arXiv2000

A combined study of $b \to s γ$ and the muon anomalous magnetic moment in gauge-mediated supersymmetry breaking models

We study both the branching ratio for $b \to s γ$ decay and the muon anomalous magnetic moment, $a_μ \equiv (g-2)_μ /2$, in the minimal supersymmetric standard model with gauge-mediated supersymmetry breaking. Combining new experimental data on $a_μ$ and the branching ratio for $b \to s γ$, useful limits on the parameter space of these models are derived. In particular, we explicitly show that, with the presently available experimental data, constraints from the decay $b \to s γ$ are more stringent than those from $a_μ$ in broad region of the parameter space. We include the supersymmetric one-loop correction to the mass of $b$ quark, $m_b$, and find that in order to have a correct value of $m_b$, the region of large tan$β$ and $μ<0$ (in our convention) is not allowed in these models (if there are no further assumptions like $b - τ$ Yukawa coupling unification). The region of large tan$β$ and $μ>0$ is also strongly constrained. We present bounds on supersymmetric particle masses as a function of $\tan β$.

hep-ph↗

arXiv1999

Constraints from the muon anomalous magnetic moment and $b \to s γ$ on gauge-mediated supersymmetry-breaking models

We present a combined study of the muon anomalous magnetic moment, $a_μ \equiv (g-2)_μ /2$, and $b \to s γ$ decay in the minimal supersymmetric standard model with gauge-mediated supersymmetry-breaking. Combining new experimental data on $a_μ$ and the branching ratio for $b \to s γ$, useful limits on the parameter space of these models are derived. Bounds on supersymmetric particle masses as a function of $\tan β$ are also presented.

hep-ph↗

arXiv1998

Alpha_s and Gauge Coupling Unification in Flipped SU(5) Models with Gauge-Mediated Supersymmetry Breaking

We examine gauge coupling unification and prediction for $α_s (M_Z)$ in minimal flipped SU(5) with gauge-mediated supersymmetry breaking. We include threshold corrections at weak scale, messenger scale and unification scale, and explicitly show that in this model there can be either \emph{one-step} or \emph{two-step} gauge coupling unification, depending on unification-scale threshold corrections. The experimental value of $α_s (M_Z)$ constrains heavy particle masses in one-step unification. In the case of two-step unification, we examine the prediction for $α_s (M_Z)$ with two-loop, light, messenger and heavy threshold corrections, and find it to be compatible with the updated experimental data.

hep-ph↗

arXiv1995

Inflation at Low Scales: General Analysis and a Detailed Model

Models of inflationary cosmology based on spontaneous symmetry breaking typically suffer from the shortcoming that the symmetry breaking scale is driven to nearly the Planck scale by observational constraints. In this paper we investigate inflationary potentials in a general context, and show that this difficulty is characteristic only of potentials $V(ϕ)$ dominated near their maxima by terms of order $ϕ^2$. We find that potentials dominated by terms of order $ϕ^m$ with \hbox{$m > 2$} can satisfy observational constraints at an arbitrary symmetry breaking scale. Of particular interest, the spectral index of density fluctuations is shown to depend only on the order of the lowest non-vanishing derivative of $V(ϕ)$ near the maximum. This result is illustrated in the context of a specific model, with a broken ${\rm SO(3)}$ symmetry, in which the potential is generated by gauge boson loops.

hep-ph↗

arXiv1995

Inflation From Symmetry Breaking Below the Planck Scale

We investigate general scalar field potentials \hbox{$V\left(ϕ\right)$} for inflationary cosmology arising from spontaneous symmetry breaking. We find that potentials which are dominated by terms of order $ϕ^m$ with \hbox{$m > 2$} can satisfy observational constraints at an arbitrary symmetry breaking scale. Of particular interest, the spectral index of density fluctuations is shown to be independent of the specific form of the potential, depending only on the order $m$ of the lowest non-vanishing derivative of $V(ϕ)$ near its maximum. The results of a model with a broken ${\rm SO(3)}$ symmetry illustrate these features.

hep-ph↗

arXiv1995

Natural Inflation From Fermion Loops

``Natural'' inflationary theories are a class of models in which inflation is driven by a pseudo-Nambu-Goldstone boson. In this paper we consider two models, one old and one new, in which the potential for inflation is generated by loop effects from a fermion sector which explicitly breaks a global $U(1)$ symmetry. In both models, we retrieve the ``standard'' natural inflation potential, $V\left(θ\right) = Λ^4\left[1 + \cos\left(θ/ μ\right)\right]$, as a limiting case of the exact one-loop potential, but we carry out a general analysis of the models including the limiting case. Constraints from the COBE DMR observation and from theoretical consistency are used to limit the parameters of the models, and successful inflation occurs without the necessity of fine-tuning the parameters.

hep-ph↗

arXiv1995

Composite Gauge fields and Broken Symmetries

A generalization of the non-Abelian version of the $CP^{N-1}$ models (also known as Grassmannian models) is presented. The generalization helps accommodate a partial breaking of the non-Abelian gauge symmetry. Constituents of the composite gauge fields, in many cases, are naturally constrained to belong to an anomaly free representation which in turn generates a composite scalar simulating Higgs mechanism to break the gauge symmetry dynamically for large $N$. Two cases are studied in detail: one based on the SU(2) gauge group and the other on SO(10). Breakings such as SU(2)$\to$U(1) or SO(10)$\to$SU(5)$\times$U(1) are found feasible. Properties of the composites fields and gauge boson masses are computed by doing a derivative expansion of the large $N$ effective action.

hep-th↗

arXiv1993

Composite gauge field models with broken symmetries

We present a generalization of the non-Abelian version of the $CP^{N-1}$ models (also known as Grassmannian models) that involve composite gauge fields to accommodate partial breaking of the non-Abelian gauge symmetry. For this to be possible, in most cases, the constituent fields need to belong to an anomaly free complex representation. Symmetry is broken dynamically for large $N$ primarily by a naturally generated composite scalar which simulates Higgs mechanism. In the example studied in some detail, the gauge group SO(10) gets broken down to subgroups like SU(5) or SU(5)$\times$U(1).

hep-th↗