arXiv subjects

K. S. Babu

Publications and source records attributed to K. S. Babu.

At least 109 records · Page 6Linked to original sources

arXiv2009

Flavor Violation in Supersymmetric Q_6 Model

We investigate flavor violation mediated by Higgs bosons and supersymmetric particles in a predictive class of models based on the non-Abelian flavor symmetry Q_6. These models, which aim to reduce the number of parameters of the fermion sector and to solve the flavor changing problems of generic SUSY setup, assume three families of Higgs bosons and spontaneous/soft violation of CP symmetry. Tree-level contributions to meson-antimeson mixings mediated by Higgs bosons are shown to be within experimental limits for Higgs masses in the (1-5) TeV range. Calculable flavor violation induced by SUSY loops are analyzed for meson mixing and lepton decays and found to be consistent with data. Significant new SUSY contributions arise in B_s- \bar{B}_s mixing, but non-standard CP violation is suppressed. A simple solution to the SUSY CP problem is found, which requires light Higgsinos.

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arXiv2009

New Mechanism for Neutrino Mass Generation and Triply Charged Higgs Bosons at the LHC

We propose a new mechanism for generating small neutrino masses which predicts the relation m_ν~ v^4/M^3, where v is the electroweak scale, rather than the conventional seesaw formula m_ν~ v^2/M. Such a mass relation is obtained via effective dimension seven operators LLHH(H*H)/M^3, which arise when an isospin 3/2 Higgs multiplet Φis introduced along with iso-triplet leptons. The masses of these particles are naturally in the TeV scale. The neutral member of Φacquires an induced vacuum expectation value and generates neutrino masses, while its triply charged partner provides the smoking gun signal of this scenario. These triply charged bosons can be pair produced at the LHC and the Tevatron, with Φ^{+++} decaying into W^+l^+l^+ or W^+W^+W^+, possibly with displaced vertices. The leptonic decays of Φ^{+++} will help discriminate between normal and inverted hierarchies of neutrino masses. This scenario also allows for raising the standard Higgs boson mass to values in excess of 500 GeV.

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arXiv2009

New Ways to Leptogenesis with Gauged B-L Symmetry

We show that in supersymmetric models with gauged B-L symmetry, there is a new source for cosmological lepton asymmetry. The Higgs bosons responsible for B-L gauge symmetry breaking decay dominantly into right-handed sneutrinos \tilde{N} and \tilde{N}* producing an asymmetry in \tilde{N} over \tilde{N}*. This can be fully converted into ordinary lepton asymmetry in the decays of \tilde{N}. In simple models with gauged B-L symmetry we show that resonant/soft leptogenesis is naturally realized. Supersymmetry guarantees quasi-degenerate scalar states, while soft breaking of SUSY provides the needed CP violation. Acceptable values of baryon asymmetry are obtained without causing serious problems with gravitino abundance.

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arXiv2008

Common Origin for CP Violation in Cosmology and in Neutrino Oscillations

We suggest predictive scenarios for neutrino masses which provide a common origin for CP violation in early universe cosmology and in neutrino oscillations. Our setup is the seesaw mechanism in the context of MSSM with two quasi-degenerate right-handed neutrinos, with baryon asymmetry generated via resonant leptogenesis. Three different models are found with specific textures in the Yukawa coupling matrices, each with a single phase which controls leptogenesis and neutrino CP violation. One model leads to normal hierarchy of light neutrino masses and the prediction tan theta_13 = sin theta_12 \sqrt{m_2/m_3}, resulting in a value of the reactor mixing angle theta_13 very close to the current experimental lower limit. The other two models predict inverted hierarchical neutrino mass spectrum with the sum rules sin^2 theta_12 = 1/2-tan theta_23 sin theta_ 13 cos delta and sin^2 theta_12 = 1/2+cot theta_23 sin theta_13 cos delta respectively. We obtain a lower bound for the phase |delta| in the normal hierarchical model, and a narrow range for |delta| for the inverted hierarchical model from cosmology. In our scenario, the mass-splitting between the quasi-degenerate right-handed neutrinos arise via renormalization group flow, which provides a lower limit on the MSSM parameter tan beta > 12. The right-handed neutrino masses can be as low as TeV, which would avoid the gravitino problem generic to supersymmetric models.

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arXiv2008

Neutrino Mass Hierarchy and neutron-anti-neutron Oscillation from Baryogenesis

It has been recently proposed that the matter-antimatter asymmetry of the universe may have its origin in "post-sphaleron baryogenesis" (PSB). It is a TeV scale mechanism that is testable at the LHC and other low energy experiments. In this paper we present a theory of PSB within a quark-lepton unified scheme based on the gauge group $SU(2)_L\times SU(2)_R\times SU(4)_c$ that allows a direct connection between the baryon asymmetry and neutrino mass matrix. The flavor changing neutral current constraints on the model allow successful baryogenesis only for an inverted mass hierarchy for neutrinos, which can be tested in the proposed long base line neutrino experiments. The model also predicts observable neutron--antineutron oscillation accessible to the next generation of experiments as well as TeV scale colored scalars within reach of LHC.

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arXiv2008

DUSEL Theory White Paper

The NSF has chosen the site for the Deep Underground Science and Engineering Laboratory (DUSEL) to be in Lead, South Dakota. In fact, the state of South Dakota has already stepped up to the plate and contributed its own funding for the proposed lab, see http://www.sanfordlaboratoryathomestake.org/index.html. The final decision by NSF for funding the Initial Suite of Experiments for DUSEL will be made early in 2009. At that time the NSF Science Board must make a decision. Of order 200 experimentalists have already expressed an interest in performing experiments at DUSEL. In order to assess the interest of the theoretical community, the Center for Cosmology and Astro-Particle Physics (CCAPP) at The Ohio State University (OSU) organized a 3-day DUSEL Theory Workshop in Columbus, Ohio from April 4 - 6, 2008. The workshop focused on the scientific case for six proposed experiments for DUSEL: long baseline neutrino oscillations, proton decay, dark matter, astrophysical neutrinos, neutrinoless double beta decay and N-Nbar oscillations. The outcome of this workshop is the DUSEL Theory White paper addressing the scientific case at a level which may be useful in the decision making process for policy makers at the NSF and in the U.S. Congress. In order to assess the physics interest in the DUSEL project we have posted the DUSEL Theory White paper on the following CCAPP link http://ccapp.osu.edu/whitepaper.html . Please read the white paper and, if you are interested, use the link to show your support by co-signing the white paper.

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arXiv2008

Higgs Boson Mass, Sparticle Spectrum and Little Hierarchy Problem in Extended MSSM

We investigate the impact of TeV-scale matter belonging to complete vectorlike multiplets of unified groups on the lightest Higgs boson in the MSSM. We find that consistent with perturbative unification and electroweak precision data the mass m_h can be as large as 160 GeV. These extended MSSM models can also render the little hierarchy problem less severe, but only for lower values of m_h < 125 GeV. We present estimates for the sparticle mass spectrum in these models.

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arXiv2008

Minimal Supersymmetric Left-Right Model with Automatic R Parity

We revisit the minimal supersymmetric left-right model with B-L=2 triplet Higgs fields and show that a self-consistent picture emerges with automatic R-parity conservation even in the absence of higher dimensional operators. By computing the effective potential for the Higgs system including heavy Majorana neutrino Yukawa couplings we show that the global minimum of the model can lie in the charge and R-parity conserving domain. The model provides natural solutions to the SUSY phase problem and the strong CP problem and makes several interesting predictions. Quark mixing angles arise only after radiative corrections from the lepton sector are taken into account. A pair of doubly charged Higgs fields remain light below TeV with one field acquiring its mass entirely via renormalization group corrections. We find this mass to be not much above the Bino mass. In the supergravity framework for SUSY breaking, we also find similar upper limits on the stau masses. Natural solutions to the $μ$ problem and the SUSY CP problem entails light SU(2)_L triplet Higgs fields, leading to rich collider phenomenology.

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arXiv2008

Predictive Model of Inverted Neutrino Mass Hierarchy and Resonant Leptogenesis

We present a new realization of inverted neutrino mass hierarchy based on $S_3 \times {\cal U}(1)$ flavor symmetry. In this scenario, the deviation of the solar oscillation angle from $π/4$ is correlated with the value of $θ_{13}$, as they are both induced by a common mixing angle in the charged lepton sector. We find several interesting predictions: $\te_{13}\geq 0.13$, $\sin^2\te_{12}\geq 0.31$, $\sin^2\te_{23}\simeq 0.5$ and $0\leq \cos \de \leq 0.7$ for the neutrino oscillation parameters and $0.01 {\rm eV}\stackrel{<}{_\sim}m_{\bt \bt}\stackrel{<}{_\sim} 0.02 {\rm eV}$ for the effective neutrino mass in neutrino-less double $\bt $-decay. We show that our scenario can also explain naturally the observed baryon asymmetry of the universe via resonant leptogenesis. The masses of the decaying right--handed neutrinos can be in the range $(10^3 - 10^7)$ GeV, which would avoid the generic gravitino problem of supersymmetric models.

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arXiv2007

Family Unification with SO(10)

Unification based on the group SO(10)^3 \times S_3 is studied. Each family has its own SO(10) group, and the S_3 permutes the three families and SO(10) factors. This is the maximal local symmetry for the known fermions. Family unification is achieved in the sense that all known fermions are in a single irreducible multiplet of the symmetry. The symmetry suppresses SUSY flavor changing effects by making all squarks and sleptons degenerate in the symmetry limit. Doublet-triplet splitting can arise simply, and non-trivial structure of the quark and lepton masses emerges from the gauge symmetry, including the "doubly lopsided" form.

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arXiv2007

Leptonic color models from Z_8 orbifolded AdS/CFT

We study orbifold compactifications of the type IIB superstring on AdS_5 x S^5/Gamma, where Gamma is the abelian group Z_8, which can lead to non-SUSY three and four family models based on quartification. In particular, we focus on two models, one fully quartified model and one a model with two trinification families and one quartification family, which reduces to the standard model with a minimal leptonic color sector.

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arXiv2007

Singlet fermion dark matter and electroweak baryogenesis with radiative neutrino mass

The model of radiative neutrino mass with dark matter proposed by one of us is extended to include a real singlet scalar field. There are then two important new consequences. One is the realistic possibility of having the lightest neutral singlet fermion (instead of the lightest neutral component of the dark scalar doublet) as the dark matter of the Universe. The other is a modification of the effective Higgs potential of the Standard Model, consistent with electroweak baryogenesis.

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arXiv2007

Unified TeV Scale Picture of Baryogenesis and Dark Matter

We present a simple extension of MSSM which provides a unified picture of cosmological baryon asymmetry and dark matter. Our model introduces a gauge singlet field $N$ and a color triplet field $X$ which couple to the right--handed quark fields. The out--of equilibrium decay of the Majorana fermion $N$ mediated by the exchange of the scalar field $X$ generates adequate baryon asymmetry for $M_N \sim 100$ GeV and $M_X \sim$ TeV. The scalar partner of $N$ (denoted $\tilde{N}_1$) is naturally the lightest SUSY particle as it has no gauge interactions and plays the role of dark matter. $\tilde{N}_1$ annihilates into quarks efficiently in the early universe via the exchange of the fermionic $\tilde{X}$ field. The model is experimentally testable in (i) neutron--antineutron oscillations with a transition time estimated to be around $10^{10}$ sec, (ii) discovery of colored particles $X$ at LHC with mass of order TeV, and (iii) direct dark matter detection with a predicted cross section in the observable range.

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arXiv2007

Missing Partner Mechanism in SO(10) Grand Unification

We present a new possibility for achieving doublet-triplet splitting naturally in supersymmetric SO(10) grand unified theories. It is based on a missing partner mechanism which is realized with the 126 + 126-bar Higgs superfields. These Higgs fields, which are also needed for generating Majorana right-handed neutrino masses, contain a pair of color triplets in excess of weak doublets. This feature enables us to remove the color triplets from the low energy spectrum without fine-tuning. We give all the needed ingredients for a successful implementation of the missing partner mechanism in SO(10) and present explicit models wherein the Higgs doublet mass is protected against possible non-renormalizable corrections to all orders. We also show how realistic fermion masses can be generated in this context.

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arXiv2006

Fermion Mass Generation in SO(10) with a Unified Higgs Sector

An analysis of generating fermion masses via cubic couplings in SO(10) grand unification with a unified Higgs sector is given. The new framework utilizes a single pair of vector--spinor representation $144+\bar{144}$ to break the gauge symmetry all the way to $SU(3)_C \times U(1)_{em}$. Typically the matter--Higgs couplings in this framework are quartic and lead to naturally suppressed Yukawa couplings for the first two generations. Here we show that much larger third generation couplings naturally arise at the cubic level with additional matter in 10--plet and 45--plet representations of SO(10). Thus the physical third generation is a mixture of 16, 10 and 45--plet representations while the remaining components become superheavy and are removed from the low energy spectrum. In this scenario it is possible to understand the heaviness of the top in a natural way since the analysis generates a hierarchy in the Yukawa couplings so that $h_{\textnormal {t}}/h_{\textnormal {b}}>> 1$ where $h_{\textnormal {t}} (h_{\textnormal {b}})$ are the top (bottom) Yukawa couplings. It is then possible to realize values of $\tanβ$ as low as 2, which also helps to stabilize the proton.

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arXiv2006

Post--Sphaleron Baryogenesis

We present a new mechanism for generating the baryon asymmetry of the universe directly in the decay of a singlet scalar field $S_r$ with a weak scale mass and a high dimensional baryon number violating coupling. Unlike most currently popular models, this mechanism, which becomes effective after the electroweak phase transition, does not rely on the sphalerons for inducing a nonzero baryon number. CP asymmetry in $S_r$ decay arises through loop diagrams involving the exchange of $W^\pm$ gauge bosons, and is suppressed by light quark masses, leading naturally to a value of $η_B \sim 10^{-10}$. We show that the simplest realization of this mechanism, which uses a six quark $ΔB=2$ operator, predicts colored scalars accessible to the LHC, and neutron--antineutron oscillation within reach of the next generation experiments.

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arXiv2005

SU(2) Family Symmetry and the Supersymmetric Spectrum

We present a supersymmetric extension of the Standard Model with a gauged SU(2) family symmetry for the leptons. It is shown that this family symmetry can be consistently broken at the TeV scale along with supersymmetry. If supersymmetry breaking is driven by anomaly mediation, this model can provide positive squared masses for the sleptons and thus cure the tachyon problem. We analyze the constraints and consequences of this scenario. A characteristic feature of this model is the non-degeneracy of the first two family sleptons. The model predicts large value of tan(beta) and observable τto e γand B to μ^+ μ^- decay rates.

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arXiv2005

Theory of Neutrinos: A White Paper

During 2004, four divisions of the American Physical Society commissioned a study of neutrino physics to take stock of where the field is at the moment and where it is going in the near and far future. Several working groups looked at various aspects of this vast field. The summary was published as a main report entitled ``The Neutrino Matrix'' accompanied by short 50 page versions of the report of each working group. Theoretical research in this field has been quite extensive and touches many areas and the short 50 page report provided only a brief summary and overview of few of the important points. The theory discussion group felt that it may be of value to the community to publish the entire study as a white paper and the result is the current article. After a brief overview of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, the white paper summarizes what can be learned about physics beyond the Standard Model from the various proposed neutrino experiments. It also comments on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe and the basic nature of neutrino interactions as well as the existence of possible additional neutrinos. Extensive references to original literature are provided.

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