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D. P. Roy

Publications and source records attributed to D. P. Roy.

At least 91 records · Page 5Linked to original sources
arXiv1998

Texture of a Four-Neutrino Mass Matrix

We propose a simple texture of the neutrino mass matrix with one sterile neutrino along with the three standard ones. It gives maximal mixing angles for $ν_e \to ν_S$ and $ν_μ\to ν_τ$ oscillations or vice versa. Thus with only four parameters, this mass matrix can explain the solar neutrino anomaly, atmospheric neutrino anomaly, LSND result and the hot dark matter of the universe, while satisfying all other Laboratory constraints. Depending on the choice of parameters, one can get the vacuum oscillation or the large angle MSW solution of the solar neutrino anomaly.

hep-ph↗
arXiv1998

Minimal See-Saw Model for Atmospheric and Solar Neutrino Oscillations

We present a minimal see-saw model based on an extension of the standard model (SM) which includes an additional U(1), with gauge charge $B - \frac{3}{2} (L_μ+ L_τ)$. Requirement of anomaly cancellation implies the existence of two right-handed singlet neutrinos, carrying this gauge charge, which have normal Dirac couplings to $ν_μ$ and $ν_τ$ but suppressed ones to $ν_e$. Assuming the U(1) symmetry breaking scale to be 10$^{12-16}$~GeV, this model can naturally account for the large (small) mixing solutions to the atmospheric (solar) neutrino oscillations.

hep-ph↗
arXiv1998

Light Charged Higgs Bosons in Supersymmetric Models

We point out that present experimental limits from searches for neutral Higgs bosons at LEP already imply stringent lower bounds on the mass of the charged Higgs boson in the Minimal Supersymmetric Standard Model (MSSM); these bounds are especially severe for low values of \tanb ($\tanb \leq 3$), where the $H^+ \bar{t} b$ coupling is large. However, these indirect constraints are much weaker in simple extensions of the MSSM Higgs sector involving the introduction of an extra U(1) gauge group or an extra $SU(2) \times U(1)_Y$ Higgs singlet field; in the latter case charged Higgs bosons can even be light enough to be pair produced at LEP.

hep-ph↗
arXiv1998

Phenomenology of the $B - 3 L_τ$ Gauge Boson

Assuming the existence of a gauge boson $X$ which couples to $B - 3 L_τ$, we discuss the present experimental constraints on $g_X$ and $m_X$ from $Z \to l^+ l^-$ and $Z \to \bar f f X~(f = q, ν_τ, τ)$. We also discuss the discovery potential of $X$ at hadron colliders through its decay into $τ^+ τ^-$ pairs. In the scenario where all three charged leptons (and their neutrinos) mix, lepton flavor nonconservation through $X$ becomes possible and provides another experimental probe into this hypothesis.

hep-ph↗
arXiv1998

Higgs and SUSY Searches at LHC

I start with a brief introduction to Higgs mechanism and supersymmetry. Then I discuss the theoretical expectations, current limits and search strategies for Higgs boson(s) at LHC --- first in the SM and then in the MSSM. Finally I discuss the signatures and search strategies for the superparticles.

hep-ph↗
arXiv1998

Pattern of Texture Zeroes in Quark Mass Matrices With a Divergent Top-Yukawa Coupling at the GUT Scale

In a SUSY GUT model responsible for generating symmetric quark mass matrices at the GUT scale (mu = Lamda) we assume that the top-Yukawa coupling, lamda_t, becomes infinite at that scale. As a consequence, the MSSM renormalization group equations for quark Yukawa couplings exhibit hierarchical solutions which lead to a pattern of texture zeroes in quark mass matrices at mu = Lamda similar to one of the solutions of Ramond, Roberts, and Ross. The evolution in energy scale to low energies shows excellent agreement between the measured quantities involving the scale-independent ratios of CKM matrix elements and their predicted values in terms of quark mass ratios. It is noted that the tt-bar condensate model of Bardeen, et al. predicts an infinite lamda_t at mu = Lamda implying, for our model, that at mu = Lamda, both the symmetry of Yukawa matrices and condensate dynamics may have a common origin.

hep-ph↗
arXiv1997

Relaxing Atomic Parity Violation Constraints on New Physics

The weak charge $Q_W$ measured in atomic parity violation experiments can receive compensating contributions from more than one new physics source. We show explicitly that the $ΔQ_W$ contribution from the exchange of an extra Z-boson can cancel that from the $s$-channel scalar top or scalar charm exchange in R-parity violating SUSY models proposed to explain the HERA high-$Q^2$ anomaly.

hep-ph↗
arXiv1997

Lower Bound on the Pseudoscalar Mass in the Minimal Supersymmetric Standard Model

In the Higgs sector of the Minimal Supersymmetric Standard Model, the mass of the pseudoscalar $A$ is an independent parameter together with $\tan β\equiv v_2/v_1$. If $m_A$ is small, then the process $e^+ e^- \to h + A$ is kinematically allowed and is suppressed only if $\tan β$ is small. On the other hand, the mass of the charged Higgs boson is now near $M_W$, and the decay $t \to b + h^+$ is enhanced if $\tan β$ is small. Since the former has not been observed, and the branching fraction of $t \to b + W$ cannot be too small (by comparing the experimentally derived $t \bar t$ cross section from the leptonic channels with the theoretical prediction), we can infer a phenomenological lower bound on $m_A$ of at least 60 GeV for all values of $\tan β$.

hep-ph↗
arXiv1997

Implications of the HERA Events for the R-Parity Breaking SUSY Signals at Tevatron

The favoured R-parity violating SUSY scenarios for the anomalous HERA events correspond to top and charm squark production via the $λ'_{131}$ and $λ'_{121}$ couplings. In both cases the corresponding electronic branching fractions of the squarks are expected to be $\ll 1$. Consequently the canonical leptoquark signature is incapable of probing these scenarios at the Tevatron collider over most of the MSSM parameter space. We suggest alternative signatures for probing them at Tevatron, which seem to be viable over the entire range of MSSM parameters.

hep-ph↗
arXiv1997

New Physics from HERA?

The H1 and ZEUS experiments at the HERA $e^\pm p$ collider at Hamburg have recently reported some anomalous hard-scattering events, which could be indicative of new physics beyond the standard model. I have tried to discuss in a nonspecialist language the significance of this result for particle physics along with its interpretation in terms of the currently popular extensions of the standard model.

hep-ph↗
arXiv1997

The Intrinsic Gluon Component of the Nucleon

Using an intrinsic parton model we estimate the rough shape and size of the intrinsic gluon component of the nucleon, corresponding to an energy scale $Q$ of the order $\lqcd$. It is nearly as hard in shape as the valence quark, while its size accounts for a quarter of the nucleon momentum. Both are in qualitative agreement with the input leading twist gluon distribution assumed by Glück, Reya and Vogt at this scale in order to reproduce the observed distributions at $Q^2 \gsim 1$ GeV$^2$ via perturbative QCD evolution.

hep-ph↗
arXiv1997

Constraints on the charged Higgs sector from the CDF Top quark data

The top quark data in the lepton plus $τ$ channel offers a viable probe for the charged Higgs boson signal. We have analysed the recent Collider Detector at Fermilab (CDF) data in this channel to obtain a significant limit on the $H^\pm$ mass in the large $\tanβ$ region.

hep-ph↗
arXiv1997

Light Higgsino Dark Matter

We re-investigate the question whether a light higgsino-like neutralino is a viable Dark Matter candidate. To this end we compute the dominant one-loop corrections to the masses of the higgsino-like states in the minimal Supersymmetric Standard Model (MSSM), due to loops involving heavy quarks and their superpartners. We also calculate analogous corrections to the couplings of higgsino-like neutralinos to Z and Higgs bosons. In the region of parameter space leading to high higgsino purity of the lightest neutralino, these corrections can change the expected relic density by up to a factor of five in either direction. We conclude that for favorable choices of soft supersymmetry breaking parameters, a state with more than 99% higgsino purity could indeed form all cold Dark Matter in the Universe. In some cases these corrections can also increase the expected cross section for LSP scattering off spinless nuclei by up to two orders of magnitude, or reduce it to zero.

hep-ph↗
arXiv1996

An R-Parity Breaking SUSY Solution to the R_b and ALEPH Anomalies

We discuss an optimal $R$-parity breaking SUSY solution to the $R_b$ excess as well as the ALEPH 4-jet anomaly. The latter arises from the pair production of stop via chargino decay at LEP1.5, followed by its $R$--violating decay into a light quark pair. The model satisfies top quark and $Z$--boson decay constraints along with gaugino mass unification.

hep-ph↗
arXiv1996

SUSY Contributions to $R_b$ and Top Decay

I report on a systematic analysis of the MSSM parameter space to obtain the best SUSY solution to the $R_b$ anomaly within the constraint of top quark decay. Phenomenological implications for top decay and direct stop production at the Tevatron collider are discussed.

hep-ph↗
arXiv1996

SUSY Contributions to R_b and Top Quark Decay

Stop contributions to radiative corrections to R_b and the top quark decay are analysed over the relevant MSSM parameter space. One sees a 30 % increase in the former along with a similar drop in the latter in going from the higgsino dominated to the mixed region. Consequently one can get a viable SUSY contribution to R_b within the constraint of the top quark data only in the mixed region, corresponding to a photino dominated LSP. We discuss the phenomenological implications of this model for top quark decay and direct stop production, which can be tested with the Tevatron data.

hep-ph↗
arXiv1996

Like Sign Dilepton Signature for R-Parity Violating SUSY Search at the Tevatron Collider

The like sign dileptons provide the most promising signature for superparticle search in a large category of $R$-parity violating SUSY models. We estimate the like sign dilepton signals at the Tevatron collider, predicted by these models, over a wide region of the MSSM parameter space. One expects an unambiguous signal upto a gluino mass of $200 - 300$ GeV ($\geq 500$ GeV) with the present (proposed) accumulated luminosity of $\sim 0.1~(1)~{\rm fb}^{-1}$.

hep-ph↗