arXiv subjects

S. Nandi

Publications and source records attributed to S. Nandi.

171 records · Page 10Linked to original sources

arXiv1997

Scalar tau Signal at LEP 2 in models with Gauge Mediated Supersymmetry Breaking

In theories with gauge mediated supersymmetry breaking, the scalar tau, (${\tilde τ_1}$) is the lightest observable superpartner for part of the parameter space. At LEP 2, the production of such a $\tilde τ_1$ pair and their subsequent decays give rise to a pair of $τ$ leptons plus missing energy from the unobserved gravitinos. The angular distributions of the $τ$'s are different from those arising from the production and decay of W pairs, and thus will constitute an interesting signal for supersymmetry. We also consider ${\tilde τ_1}$ pair production in the complementary part of parameter space where the lightest neutralino is lighter than the $\tilde τ_1$.

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arXiv1997

An Unusual Signal for Supersymmetry at the Tevatron

We propose a new scenario in which the dominant signal for supersymmetry at the Tevatron are the events having two or three $τ$ leptons with high $p_T$ accompanied by large missing transverse energy. This signal is very different from the multijet or multileptons (involving $e$ and/or $μ$ only) or the photonic signals that have been extensively investigated both theoretically and experimentally. A large region of the GMSB parameter space with the lighter stau as the NLSP allow this possibility. Such a signal may be present in the past Tevatron data to be analyzed.

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arXiv1997

New Messenger Sector for Gauge Mediated Supersymmetry Breaking

We propose a new class of gauge mediated supersymmetry breaking models where the standard model gauge group is embedded into the gauge group $SU(2)_L\times U(1)_{I_{3R}}\times U(1)_{B-L}$ [or $SU(2)_L\times SU(2)_R\times U(1)_{B-L}$] at the supersymmetry breaking scale $Λ_S$. The messenger sector in these models can consist of color singlet but $U(1)_{I_{3R}}$ and $U(1)_{B-L}$ nonsinglet fields. The distinguishing feature of these models are (i)exact R-parity conservation, (ii) nonvanishing neutrino masses and (iii) a unified hidden and messenger sector potential. The simplest version of these models predicts the existence of light gluinos which can however be made heavier by a simple modification of the supersymmetry breaking sector.

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arXiv1997

Explaining the HERA Anomaly Without Giving Up R-parity Conservation

We point out that in extended supersymmetric models such as supersymmetric left-right models, it is possible to have leptoquarks that explain the HERA high $Q^2$ anomaly without giving up R-parity conservation. The leptoquarks belong to vectorlike $(2, 2, \pm{4/3}, 3 or 3^*) $ representations of $SU(2)_L\times SU(2)_R\times U(1)_{B-L}\times SU(3)_c$ (denoted $G_{2213}$). Unlike the R-parity violating scenario, the leptoquarks are accompanied by new superpartners,the leptoquarkino which leads to many intersting signatures in other collider experiments. At Tevatron, pair productions of the leptoquarkino will give rise to dilepton signals very distinct from the top productions. These models can lead to unification of gauge coupling constants at a scale of around $10^{10}$ GeV implying that grand unification group is not of the usual SU(5) or SO(10) types but rather an automatically R-parity conserving $SU(5)\times SU(5)$ GUT model recently proposed by one of the authors (R. N. M.) which leads to a stable proton.

hep-ph↗

arXiv1997

A new signature for gauge mediated supersymmetry breaking

In theories with gauge mediated supersymmetry breaking, the scalar tau, (${\tilde τ_1}$) is the lightest superpartner for a large range of the parameter space. At the large electron positron collider (LEP 2) this scenario can give rise to events with four $τ$ leptons and large missing energy. Two of the $τ$'s ( coming from the decays of ${\tilde τ_1}$'s ) will have large energy and transverse momentum, and can have similar sign electrical charges. Such events are very different from the usual photonic events that have been widely studied, and could be a very distinct signal for the discovery of supersymmetry.

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arXiv1996

Texture of fermion mass matrices in partially unified theories

We investigate the texture of fermion mass matrices in theories with partial unification (for example $ SU(2)_L\times SU(2)_R\times SU(4)_c$) at a scale $\sim 10^{12}$ GeV. Starting with the low energy values of the masses and the mixing angles, we find only two viable textures with atmost four texture zeros. One of these corresponds to a somewhat modified Fritzsch textures. A theoretical derivataion of these textures leads to new interesting relations among the masses and the mixing angles.

hep-ph↗

arXiv1996

New Collider Bound on Light Gravitino Mass

In supergravity theories with a very light gravitino, the gluino decays dominantly to a gluon and a gravitino. This results in a much larger missing $E_T$ for the multijet final states in hadronic colliders. We use the latest Tevatron data for the multijet final states to set a new absolute lower bound of 3.0 x 10^{-13} GeV for the light gravitino mass.

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arXiv1995

A new ansatz: Fritzsch Mass Matrices with least modification

We investigate how the Fritzsch ansatz for the quark mass matrices can be modified in the least possible way to accommodate the observed large top quark mass and the measured values of the CKM elements. As one of the solutions, we find that the \{23\} and the \{32\} elements of the up quark mass matrix are unequal. The rest of the assumptions are same as in Fritzsch ansatz. In this formalism we have an extra parameter i.e. the ratio of the \{23\} and the \{32\} element, which gets fixed by the large top quark mass. The predicted values for $\frac{V_{ub}}{V_{cb}}$ , $\frac{V_{td}}{V_{ts}}$ from this new ansatz are in the correct experimental range even for the smaller values of $\tan β$. In the end, we write down the $SO(10)$ motivated superpotential for these new mass matrices.

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arXiv1994

Top Quark Signature in Extended Color Theories

We consider the implications of an extended color group, $SU\left( 3\right) _I\times SU\left( 3\right) _{II}$, spontaneously broken to $SU\left( 3\right) _c$ at a TeV or lower scale, for the hadronic colliders. The associated massive color octet gauge bosons (the colorons) can enhance the $t \overline{t}$ pair production at the Tevatron collider. At the LHC, the colorons can be pair produced, each decaying to a $t\overline{t}$ pair. This gives rise to anomalous multi W production: a clear signature of physics beyond the Standard Model. We calculate the associated multijet and multilepton final states at the Tevatron and the LHC energies, and compare these with the expectations from the Standard Model.

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