arXiv subjects

Sudhir K. Vempati

Publications and source records attributed to Sudhir K. Vempati.

50 records · Page 3Linked to original sources

arXiv2007

Results from MiniBooNE

The long awaited experimental results from MiniBooNE have recently been announced. This experiment tests whether neutrino oscillations can occur at a higher mass squared difference $\sim1 {eV}^2$ compared to well established observations of solar and atmospheric neutrinos. The LSND experiment has previously claimed to have observed neutrino oscillations at $Δm^2 \sim 1 {eV}^2$, however the results being controversial, required an independent confirmation. The MiniBooNE results settle this controversy by observing null oscillations at the said mass squared difference. These results have strong implications on existence of sterile neutrinos, CPT violation and mass varying neutrinos. We review the present status of neutrino masses and mixing in the light of this recent result.

physics.pop-ph↗

arXiv2005

Large D-terms, hierarchical soft spectra and moduli stabilisation

We derive general expressions for soft terms in supergravity where D-terms contribute significantly to the supersymmetry breaking in addition to the standard F-type breaking terms. Such D-terms can strongly influence the scalar mass squared terms, while having limited impact on gaugino masses and the B-terms. We present parameterisations for the soft terms when D-terms dominate over F-terms or become comparable with them. Novel patterns emerge which can be tested phenomenologically. In a mixed anomaly-D mediated scenario, the scalars have masses from D-mediation, whereas gaugino masses are generated by anomaly mediation. As an application of this analysis, we show that while the "split supersymmetry" like mass spectrum with one fine tuned Higgs is not an automatic outcome of these scenarios, explicit models can be constructed where it can be realised. Finally, we show that large D-mediated supersymmetry breaking can be realised in string models based on intersecting D-branes. Examples are presented where the moduli are stabilised in the presence of large D-terms using non-perturbative gaugino condensation like effects.

hep-th↗

arXiv2005

A Predictive Seesaw Scenario for EDMs

The generation of electric dipole moments (EDMs) is addressed in the supersymmetric seesaw scenario realized through the exchange of SU(2)_W triplet states. In particular, we show that the triplet soft-breaking bilinear term can induce finite contributions to lepton and quark EDMs. Moreover, the peculiar flavour structure of the model allows us to predict the EDM ratios d_e/d_mu and d_mu/d_tau only in terms of the neutrino parameters.

hep-ph↗

arXiv2004

Massive Neutrinos and Flavour Violation

In spite of the large lepton flavour violation (LFV) observed in neutrino oscillations, within the Standard Model, we do \textit{not} expect any visible LFV in the charged lepton sector ($μ\to e, γ$, $τ\to μ, γ$, etc.). On the contrary, the presence of new physics close to the electroweak scale can enhance the amplitudes of these processes. We discuss this in general and focus on a particularly interesting case: the marriage of low-energy supersymmetry (SUSY) and seesaw mechanism for neutrino masses (SUSY seesaw). Several ideas presented in this context are reviewed both in the bottom-up and top-down approaches. We show that there exist attractive models where the rate for LFV processes can attain values to be probed in pre-LHC experiments.

hep-ph↗

arXiv2003

Seesaw and Lepton Flavour Violation in SUSY SO(10)

That $μ\to e, γ$ and $τ\to μ,γ$ are sensitive probes of SUSY models with a see-saw mechanism is a well accepted fact. Here we propose a `top-down' approach in a general SUSY SO(10) scheme. In this framework, we show that at least one of the neutrino Yukawa couplings is as large as the top Yukawa coupling. This leads to a strong enhancement of these leptonic flavour changing decay rates. We examine two `extreme' cases, where the lepton mixing angles in the neutrino Yukawa couplings are either small (CKM-like) or large (PMNS-like). In these two cases, we quantify the sensitivity of leptonic radiative decays to the SUSY mass spectrum. In the PMNS case, we find that the ongoing experiments at the B-factories can completely probe the spectrum up to gaugino masses of 500 GeV (any tan $β$). Even in the case of CKM-like mixings, large regions of the parameter space will be probed in the near future, making these two processes leading candidates for indirect SUSY searches.

hep-ph↗

arXiv2002

Bi-maximal mixing and Bilinear R violation

We perform a general analytic study of feasibility of obtaining a combined explanation for the deficits in the solar and the atmospheric neutrino fluxes with two large mixing angles in supersymmetric model with bilinear R parity violations. The required hierarchy among the solar and atmospheric neutrino mass scales follows in this framework in the presence of an approximate Higgs - slepton universality at the weak scale. The solar mixing angle is shown to be related to non-universality in slepton mass terms specifically to differences in soft parameters of the first two leptonic generations. It is shown that this flavour universality violation should be as strong as the Higgs-slepton universality violation if solar neutrino mixing angle is to be large. The standard supergravity models with universal boundary conditions at a high scale lead to the required Higgs-slepton universality violations but the predicted violation of flavour universality among the first two generations is much smaller than required. This model therefore cannot provide an explanation of large solar neutrino mixing angle unless some universality violations in soft supersymmetry breaking parameters are introduced at a high scale itself.

hep-ph↗

arXiv2002

Studies in Topics Going beyond the Standard Electroweak Model

Supersymmetric Standard Model has been built to solve the hierarchy problem which is encountered whenever Standard Model is incorporated into a theory with a larger mass scale. Experimentally, one of the first signals of physics beyond Standard Model is provided by the atmospheric neutrino experiments which indicate the existence of at least one non-zero neutrino mass. An interpretation of both solar and atmospheric neutrino anomalies in terms of neutrino oscillations would lead to specific patterns for neutrino masses and mixing. In this thesis, we studied the possibilities of generating the required neutrino mass patterns in the context of supersymmetric standard models with lepton number (L) violation. After an introduction to supersymmetric standard models in Chapter 1, we give an overview of neutrino phenomenology in chapter 2. Chapter 3 discusses analytical and semi-analytical solutions to Renormalisation Group Equations (RGE) with lepton number violating couplings in the superpotential. Neutrino masses with bilinear L violation in the context of gauge mediated supersymmetric models (GMSB) are discussed in Chapter 4, where 2-loop RGE for the parameter $ΔB_i$ are presented. Chapter 5 discusses neutrino mass structure when L violation is through trilinear lepton number violating terms. Chapter 6 discusses RG enhancement of neutrino masses and neutrino mass bounds on trilinear lepton number violating couplings in the context of mSUGRA. Chapter 7 summarises general features of neutrino masses within these models and contains overall conclusions based on the work presented in the thesis.

hep-ph↗

arXiv2001

Constraints On Radiative Neutrino Mass Models From Oscillation Data

The three neutrino Zee model and its extension including three active and one sterile species are studied in the light of new neutrino oscillation data. We obtain analytical relations for the mixing angle in solar oscillations in terms of neutrino mass squared differences. For the four neutrino case, we obtain the result $\mathsf{sin^2 2 θ_\odot \approx 1 - [ (Δm^2_{Atm})^2/(4 Δm^2_{LSND} Δm^2_\odot) ]^2}$, which can accommodate both the large and small mixing scenarios. We show that within this framework, while both the SMA-MSW and the LMA-MSW solutions can easily be accommodated, it would be difficult to reconcile the LOW-QVO solutions. We also comment on the active-sterile admixture within phenomenologically viable textures.

hep-ph↗

arXiv2001

Neutrino Anomalies in Gauge Mediated Model with Trilinear R violation

The structure of neutrino masses and mixing resulting from trilinear $R$ violating interactions is studied in the presence of the gauge mediated supersymmetry breaking. Neutrino masses arise in this model at tree level through the RG-induced vacuum expectation values of the sneutrinos and also through direct contribution at 1-loop. The relative importance of these contributions is determined by the values of the strong and weak coupling constants. In case of purely $λ'$ couplings, the tree contribution dominates over the 1-loop diagram. In this case, one simultaneously obtains atmospheric neutrino oscillations and quasi-vacuum oscillations of the solar neutrinos if all the $ł'$ couplings are assumed to be of similar magnitudes. If R parity violation arises from the trilinear $ł$ couplings, then the loop induced contribution dominates over the tree level. One cannot simultaneously explain the solar and atmospheric deficit in this case if all the $ł$ couplings are of similar magnitude. This however becomes possible with hierarchical $ł$ and we give a specific example of this.

hep-ph↗

arXiv2000

U(1) symmetry and R parity violation

The patterns of $R$ violation resulting from imposition of a gauged U(1) horizontal symmetry on the minimal supersymmetric standard model are systematically analyzed. We concentrate on class of models with integer U(1) charges chosen to reproduce the quark masses and mixings as well as charged lepton masses exactly or approximately. The U(1) charges are further restricted by the requirement that very large bilinear lepton number violating terms should not be allowed in the superpotential. It is shown that this leads to severely constrained patterns of trilinear interactions. Specifically, only choice compatible with phenomenological restrictions is the one in which all the trilinear $λ'_{ijk}$ and all but at most two trilinear $λ_{ijk}$ couplings vanish or are enormously suppressed. The U(1) symmetry can allow effective generation of bilinear lepton number violating parameters through terms in the Kahler potential. Resulting models are identified and structure of neutrino masses in some of these is briefly discussed.

hep-ph↗

arXiv1999

Sneutrino Vacuum Expectation Values and Neutrino Anomalies Through Trilinear R-parity Violation

Neutrino mass spectrum is reanalyzed in supersymmetric models with explicit trilinear $R$ violation. Models in this category are argued to provide simultaneous solution to the solar and atmospheric neutrino anomalies. It is shown specifically that large mixing and hierarchical masses needed for the vacuum solution of neutrino anomalies arise naturally in these models without requiring any additional symmetries or hierarchies among the trilinear couplings.

hep-ph↗

arXiv1998

Gauge mediated supersymmetry breaking and neutrino anomalies

Supersymmetric standard model with softly broken lepton symmetry provides a suitable framework to accommodate the solar and atmospheric neutrino anomalies. This model contains a natural explanation for large mixing and hierarchal masses without fine tuning of the parameters. Neutrino spectrum is particularly constrained in the minimal messenger model (MMM) of gauge mediated SUSY breaking, since all SUSY breaking effects are controlled in MMM by a single parameter. We study the structure of neutrino masses and mixing both in MMM and in simple extensions of it in the context of solar and atmospheric neutrino anomalies.

hep-ph↗

arXiv1997

On the charm-squark interpretation of the HERA events

The charm squark resonance in the $e^+ q$ channel provides one of the plausible interpretations of the reported anomaly at HERA. We show that the relevant $R$ violating coupling $λ'_{121}$ is required to be large, typically around 0.1 in a large class of supergravity based models including the minimal one with the universal boundary condition at the GUT scale. Existing constraints on this coupling are reanalysed in this light and it is argued that a large $λ'_{121}$ may be feasible but would require fine tuned cancelations.

hep-ph↗

arXiv1997

Neutrino Mass Constraints on R violation and HERA anomaly

R parity violating trilinear couplings $λ'_{1jk}$ of the minimal supersymmetric standard model (MSSM) are constrained from the limit on the electron neutrino mass. Strong limits on these couplings follow from the earlier neglected contribution due to sneutrino vacuum expectation values. The limits on most of the $λ'_{1jk}$ couplings derived here are stronger than the existing ones for a wide range in parameters of MSSM. These limits strongly constrain the interpretation of recent HERA results in $e^+ p$ scattering in terms of production of squarks through $R$ violating couplings. In particular, the interpretation in terms of $\tilde{t}_L$ production off strange quark as suggested recently is not viable for wide ranges in MSSM parameters.

hep-ph↗