arXiv subjects

Bhaskar Dutta

Publications and source records attributed to Bhaskar Dutta.

230 records · Page 13Linked to original sources

arXiv2005

The $B \to Kπ$ Puzzle and Supersymmetric Models

In the light of new experimental results on $B \to Kπ$ decays, we study the decay processes $B \to K π$ in the framework of both R-parity conserving (SUGRA) and R-parity violating supersymmetric models. We find that any possible deviations from the Standard Model indicated by the current data for the branching ratios and the direct CP asymmetries of $B \to Kπ$ can be explained in both R-parity conserving SUGRA and R-parity violating SUSY models. However, there is a difference between the predictions of both models to the time-dependent CP asymmetry observable $S_{K_{_S} π^0}$ whose current experimental results include large uncertainties. We demonstrate that this difference can be useful for testing both models with more accurate data for $S_{K_{S} π^0}$ and $A_{CP}^{+-}$ in the near future.

hep-ph↗

arXiv2005

Neutrino Mixing Predictions of a Minimal SO(10) Model with Suppressed Proton Decay

During the past year, a minimal renormalizable supersymmetric SO(10) model has been proposed with the following properties: it predicts a naturally stable dark matter and neutrino mixing angles theta_atm and theta_13 while at the same time accommodating CKM CP violation among quarks with no SUSY CP problem. Suppression of proton decay for all allowed values of tan beta strongly restricts the flavor structure of the model making it predictive for other processes as well. We discuss the following predictions of the model in this paper, e.g. down-type quark masses, and neutrino oscillation parameters, U_e3, delta_MNSP, which will be tested by long baseline experiments such as T2K and subsequent experiments using the neutrino beam from JPARC. We also calculate lepton flavor violation and the lepton asymmetry of the Universe in this model.

hep-ph↗

arXiv2005

The Stau Neutralino Co-annihilation Region at an International Linear Collider

We probe the stau-neutralino co-annihilation domain of the parameter space allowed by the current experimental bounds on the light Higgs mass, the b-> s γdecay, and the amount of neutralino cold dark matter within the framework of minimal SUGRA models at a 500 GeV e+e- linear collider. The most favorable signals of SUSY are stau pair production and neutralino pair production where the small mass difference between the lighter stau and the lightest neutralino in the co-annihilation region is ~5-15 GeV and hence generates low-energy tau leptons in the final state. This small mass difference would be a striking signal of many SUGRA models. We find that a calorimeter covering down to 1^o from the beams is crucial to reduce the two-photon background and the mass difference could be measured at a level of 10% with 500 fb^-1 of data where an invariant mass of two-tau jets and missing energy is used as a discriminator.

hep-ph↗

arXiv2005

Split Supersymmetry in Unified Models

In the context of split supersymmetry, the gaugino mass spectrum seems to be very important to satisfy the dark matter content of the universe and the gauge coupling unification. In this paper, we have considered various sources of gaugino masses in the context of unified models. We show that the gaugino mass spectrum varies in different unification pictures. In the context of SU(5), we have found that the Bino/Wino mass ratio can be close to one at the weak scale which is helpful to satisfy the WMAP data. The gluino/Wino mass ratio is also different from the usual scenario of unified gaugino masses. The gaugino masses can be around one TeV and m_SUSY is chosen so that the gluino mass does not create any cosmological problem. In the context of the Pati-Salam model, we show that the gluino mass can be made very heavy even after maintaining the unification of the gauge couplings.

hep-ph↗

arXiv2005

Minimal SUGRA Model and Collider Signals

The SUSY signals in the dominant stau-neutralino coannihilation region at a 500(800) GeV linear collider are investigated. The region is consistent with the WMAP measurement of the cold dark matter relic density as well as all other current experimental bounds within the mSUGRA framework. The signals are characterized by an existence of very low-energy tau leptons in the final state due to small mass difference between stau_1 and chi_1 (5-15 GeV). We study the accuracy of the mass difference measurement with a 1^deg active mask to reduce a huge SM two-photon background.

hep-ph↗

arXiv2004

Suppressing Proton Decay in the Minimal SO(10) Model

We show that in a class of minimal supersymmetric SO(10) models which have been found to be quite successful in predicting neutrino mixings, all proton decay modes can be suppressed by a particular choice of Yukawa textures. This suppression works for contributions from both left and right operators for nucleon decay and for arbitrary \tanβ. The required texture not only fits all lepton and quark masses as well as CKM parameters but it also predicts neutrino mixing parameter U_e3 and Dirac CP phase \sin|δ_MNS| to be 0.07-0.09 and 0.3-0.7 respectively. We also discuss the relation between the GUT symmetry breaking parameters for the origin of these textures.

hep-ph↗

arXiv2004

Some Results in M-Theory Inspired Phenomenology

We consider string phenomenological models based on 11D Horava-Witten M-theory with 5 branes in the bulk. If the 5-branes cluster close to the distant orbifold plane (d_n\equiv 1-z_n\simeq 0.1) and if the topological charges of the physical plane vanish (β^{(0)}_i=0), then the Witten εterms (to first order) are correctly small and a qualitative picture of the quark and lepton mass hierarchy arises without significant fine tuning. If right handed neutrinos exist, a possible gravitationally induced cubic holomorphic contribution to the Kahler potential can exist scaled by the 11D Planck mass. These terms give rise to Dirac neutrino masses at the electroweak scale. This mechanism (different from the see-saw mechanism) is seen to account for both the atmospheric and solar neutrino oscillations. The model also gives rise to possible non-universal soft breaking A parameters in the u and d second and third generation quark sector (A_{2,3}^{(u,d)}) which naturally can account for the possible (2.4σ) break down of the Standard Model predictions in the recent B-factory data for the B->ϕK_s decays.

hep-ph↗

arXiv2004

Neutrino Masses and Mixings in a Predictive SO(10) Model with CKM CP Violation

It has recently been shown that a minimal SO(10) model with a single {\bf 10} and single {\bf 126} Higgs field breaking B-L symmetry predicts large solar and atmospheric mixings in agreement with observations if it is assumed that the neutrino mass obeys the type II seesaw formula. No additional symmetries need to be assumed for this purpose. Understanding CP violation in the renormalizable version of the model however requires a significant non-CKM source. In this paper we show that if we extend the model by the inclusion of a heavy {\bf 120} dimensional Higgs field, then it can accomodate CKM CP violation while remaining predictive in the neutrino sector. Among the predictions are:(i) solar mixing angle in the observed range; (ii)θ_{13} in the range of 0.1 to 0.26; (iii) the Dirac phase close to maximal for the central value of the solar mixing angle.

hep-ph↗

arXiv2004

CKM CP Violation in a Minimal SO(10) Model for Neutrinos and Its Implications

A minimal supersymmetric SO(10) model with one {\bf 10} and one {\bf 126} Higgs superfield has recently been shown to predict all neutrino mixings as well as the solar mass difference squared in agreement with observations. Two assumptions critical to the predictivity and success of the model are that: (i) the superpotential includes only renormalizable terms, thereby limiting the number of free parameters and (ii) the triplet term in the type II seesaw formula for neutrino mass dominates, leading to the sum rule M_nu = c(M_d - M_e) that is responsible for large mixings. However, CKM CP phase is constrained to be in the second or third quadrant requiring a significant non-CKM component to CP violation to explain observations. We revisit this issue using type I seesaw formula for neutrino masses and obtain the following results: (i) we show that the above sumrule responsible for large mixing angles can also emerge in type I seesaw models; the detailed predictions are however not compatible with present data for any choice of CP phases. (ii) We then show that addition of a nonrenormalizable term restores compatibility with neutrino data and CKM CP violation both in type I and type II cases. We further find that (iii) the MSSM parameter tan beta > 30 in the type I model and (iv) lepton flavor violation and lepton electric dipole moments which are accessible to proposed experiments in both type I and type II models. We also discuss the unification of the gauge couplings in type I model which requires an intermediate scale.

hep-ph↗

arXiv2004

CP Asymmetries of $B \to ϕK$ and $B \to η^{(\prime)} K$ Decays Using a Global Fit in QCD Factorization

We analyze the CP asymmetries of $B\to ϕK$ and $B\to η^{(\prime)} K$ modes in the QCD improved factorization framework. For our calculation we use the phenomenological parameters predetermined from the global fit for the available $B\to PP$ and $VP$ modes (without the quark-level subprocess $b\to s\bar s s$). We show that the large negative $\sin (2ϕ_1)_{ϕK_s}$ and the large branching ratio for $B^{\pm}\to η' K^{\pm}$ can be simultaneously explained in the context of supersymmetry (SUSY). The R-parity conserving SUGRA models are used and their parameter space is constrained with the observed dark matter relic density along with other experimental constraints. The R-parity violating SUSY models are also used to show that they can provide solutions. We calculate the CP asymmetries for different $B^{\pm (0)} \to ϕK^{\pm (0)}$ and $B^{\pm (0)} \to η^{(')} K^{\pm (0)}$ modes and show that the SUSY model predictions are consistent with the available experimental data.

hep-ph↗

arXiv2004

An Analysis of $B \to η' K$ Decays Using a Global Fit in QCD Factorization

In the framework of QCD factorization, we study $B^{+(0)} \to η' K^{+(0)}$ decays. In order to more reliably determine the phenomenological parameters $X_H$ and $X_A$ arising from end-point divergences in the hard spectator scattering and weak annihilation contributions, we use the global analysis for twelve $B \to PP$ and $VP$ decay modes, such as $B \to ππ$, $πK$, $ρπ$, $ρK$, etc, but excluding the modes whose (dominant) internal quark-level process is $b \to s \bar s s$. Based on the global analysis, we critically investigate possible magnitudes of $X_{H,A}$ and find that both large and small $X_{H,A}$ terms are allowed by the global fit. In the case of the large $X_{H,A}$ effects, the standard model (SM) prediction of the branching ratios (BRs) for $B^{+(0)} \to η' K^{+(0)}$ is large and well consistent with the experimental results. In contrast, in the case of the small $X_{H,A}$ effects, the SM prediction for these BRs is smaller than the experimental data. Motivated by the recent Belle measurement of $\sin (2ϕ_1)$ through $B^0 \to ϕK_s$, if we take into account possible new physics effects on the quark-level process $b \to s \bar s s$, we can explicitly show that these large BRs can be understood even in the small $X_{H,A}$ case. Specifically, we present two new physics scenarios: R-parity violating SUSY and R-parity conserving SUSY.

hep-ph↗

arXiv2003

Lepton Electric Dipole Moments, Supersymmetric Seesaw and Leptogenesis Phase

We calculate the lepton electric dipole moments in a class of supersymmetric seesaw models and explore the possibility that they may provide a way to probe some of the CP violating phases responsible for the origin of matter via leptogenesis. We show that in models where the right handed neutrino masses, $M_R$ arise from the breaking of local B-L symmetry by a Higgs field with B-L=2, some of the leptogenesis phases can lead to enhancement of the lepton dipole moments compared to the prediction of models where $M_R$ is either directly put in by hand or is a consequence of a higher dimensional operator.

hep-ph↗

arXiv2003

Sleptogenesis

We propose that the observed baryon asymmetry of the Universe can naturally arise from a net asymmetry generated in the sleptonic sector at fairly low reheat temperatures. The best candidate is indeed the right-handed sneutrino. The initial asymmetry in the sneutrino sector can be produced from the decay of the inflaton, and is subsequently transferred into the Standard Model (s)lepton doublet via the decay of the sneutrino. The active sphalerons then reprocess the leptonic asymmetry into the baryonic asymmetry. The marked feature of this scenario is that the lepton asymmetry is decoupled from the neutrino Yukawa sector. We exhibit that our scenario can be embedded within models which seek the origin of a tiny mass for neutrinos.

hep-ph↗

arXiv2000

Low-Scale and Gauge-Mediated Supersymmetry Breaking at the Fermilab Tevatron Run II

The prospects for discovering and studying signals of low-scale supersymmetry breaking models at the Tevatron Run II and beyond are explored. These models include gauge-mediated supersymmetry breaking as the most compelling and concrete realization, but more generally are distinguished by the presence of a nearly massless Goldstino as the lightest supersymmetric particle. The next-lightest supersymmetric particle(s) (NLSP) decays to its partner and the Goldstino. Depending on the supersymmetry breaking scale, these decays can occur promptly or on a scale comparable to or larger than the size of a detector. A systematic analysis based on a classification in terms of the identity of the NLSP and its decay length is presented. The various scenarios are discussed in terms of signatures and possible event selection criteria. The Run II and beyond discovery and exclusion reaches, including the effects of background, are detailed for the most compelling cases. In addition to standard event selection criteria based on missing energy and photons, leptons, jets, taus, tagged b-jets, or reconstructed Z-bosons, more exotic signals of metastable NLSPs such as displaced photons, large negative impact parameter tracks, kink tracks, both opposite and same-sign highly ionizing tracks, time of flight measurements, charge-changing tracks, charge-exchange tracks, and same-sign di-top events are investigated. The interesting possibility of observing a Higgs boson signal in events that are efficiently "tagged" by the unique signatures of low-scale supersymmetry breaking is also considered.

hep-ph↗