arXiv subjects

Debajyoti Choudhury

Publications and source records attributed to Debajyoti Choudhury.

At least 127 records · Page 7Linked to original sources

arXiv2000

Prospects of Squark & Slepton searches at a Gamma Gamma Collider

We examine the prospects of detecting sfermions at a gamma gamma collider. Once produced, a slepton can decay into a pair of quarks (jets) through R-parity violating interactions. Similarly, a squark may decay into a lepton-quark pair. Analyzing the corresponding Standard Model backgrounds, namely 4-jet and dilepton plus dijet final states respectively, we show that the sfermion can be detected almost right upto the kinematic limit and its mass determined to a fair degree of accuracy. Similar statements also hold for nonsupersymmetric leptoquarks and diquarks.

hep-ph↗

arXiv2000

On Stability of the Three 3-brane Model

We show that the Goldberger-Wise mechanism for the three 3-brane scenario proposed by Kogan et al. stabilizes the radion. We find that the system of 3-branes stabilizes in such a way that the loss in the scale factor is insignificant. That is, the negative tension brane chooses to stay close to the visible brane.

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arXiv2000

A supersymmetric solution to the KARMEN time anomaly

We interpret the KARMEN time anomaly as being due to the production of a (dominantly bino) neutralino with mass 33.9 MeV, which is the lightest supersymmetric particle but decays into 3 leptons through the violation of R-parity. For independent gaugino masses M_1 and M_2 we find regions in the (M_1, M_2, mu, tan beta) parameter space where such a light neutralino is consistent with all experiments. Future tests of this hypothesis are outlined.

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arXiv1999

CP-violating Anomalous $WWγ$ Couplings in e^+e^- Collisions

We investigate the sensitivity of future linear collider experiments to CP violating $WWγ$ couplings in the process $e^{+}e^{-} \to ν\barνγ$. We consider several sets of machine parameters: centre of mass energies $\sqrt{s}$ = 350, 500 and 800 GeV and operating at different luminosities. From an analysis of the differential cross-section the following 95% C.L. limits $|\tildeκ_γ| < 0.18$, $|\tildeλ_γ| < 0.069$ are estimated to be obtained at a future 500 GeV LC with an integrated luminosity of $125 \fb^{-1}$, a great improvement as compared to the LEP2 reach, where a senstitivity of order 2 for both couplings is found.

hep-ph↗

arXiv1998

A supersymmetric resolution of the anomaly in charmless nonleptonic $B$-decays

We examine the large branching ratio for the process $B\to η^{\prime} K$ from the standpoint of R parity violating supersymmetry. We have given all possible $R_p$ violating contributions to $B\to η^{\prime} K$ amplitudes. We find that only two pairs of $λ^{\prime}$-type $R_p$ violating couplings can solve this problem after satisfying all other experimental bounds. We also analyze those modes where these couplings can appear, {\em e.g.}, $B^\pm \to π^{\pm}K^0$, $B^{\pm,0} \to K^{*\pm,0} η^{(\prime)}$, $B^{\pm} \toϕK^{\pm}$ etc., and predict their branching ratios. Further, one of these two pairs of couplings is found to lower the branching ratio of $B^{\pm}\toϕK^\pm$, thereby allowing larger $ξ\equiv{1\over N_c}$. This allows us to fit $B^{\pm}\to ωK^{\pm}$ and $B^{\pm}\to ωπ^{\pm}$, which could not be done in the SM framework.

hep-ph↗

arXiv1998

Semileptonic charm decay as a test for the spectator model in the $B_c$-meson

The $b$ and the $c$ quark compete with each other in decays of the $B_c$-meson. We emphasize the need of obtaining reliable signals of $c \to s$ in order to assess the merits of the spectator approximation in calculating the relative strengths of the two types of decays. This, we argue, can be done by considering the decay $B_c \to B_s (B_s^*) l \bar{ν_l}$, followed by semileptonic decays of the $B_s$. We suggest looking for like-sign dileptons together with a $D_s$ at the BTeV or LHC-B experiments, and show that such signals can be made background-free by suitable event selection.

hep-ph↗

arXiv1998

Higgs Boson Signals in Three b-jet Final States at the Fermilab Tevatron

At the Fermilab Tevatron, final states with three tagged b-jets could play an important role in searches for a Higgs boson with mass in the range 100-300 GeV. These signals arise from gb fusion and we demonstrate their observability in the limit of a large b-quark Yukawa coupling. Rather promising discovery limits on such a coupling are obtained and consequent effects on the parameter space of the Higgs-boson sector in the MSSM are discussed.

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arXiv1998

Signals of R-Parity Violation at a Muon Collider

We investigate the effects of R-parity-violating $LL\bar E$ and $LQ\bar D$ operators on the production of fermion pairs at a $μ^+ μ^-$ collider with high energy and luminosity. We show that comparison of angular distributions leads to useful discovery limits for the R-parity-violating couplings, especially if the exchanged sfermions turn out to be heavy. Products of these couplings can also be probed well beyond present experimental limits, especially for the second and third generations. Finally, we compare results at a muon collider with those obtainable from an $e^+ e^-$ linear collider with similar energy and luminosity.

hep-ph↗

arXiv1998

Estimates of Long-distance Contributions to the $B_s \to γγ$ Decay

We present first calculations of new long-distance contributions to $B_s \to γγ$ decay due to intermediate $D_s$ and $D_s^*$ meson states. The relevant $γ$ vertices are estimated using charge couplings and transition moment couplings. Within our uncertainties, we find that these long-distance contributions could be comparable to the known short-distance contributions. Since they have different Cabibbo-Kobayashi-Maskawa matrix-element factors, there may be an interesting possibility of observing CP violation in this decay.

hep-ph↗

arXiv1998

Observing Doubly Charged Higgs Bosons in Photon-Photon Collisions

We discuss the possibility of observing doubly charged Higgs bosons in $γγ$ collisions. We find that one can increase the range of observability close to the kinematic limit by a judicious choice of the polarisations of the initial $e^-/ e^+$ beams as well as the initial laser beam photons which are made to back-scatter from the former. We also note that, in a large region of parameter space, the generally used lepton number violating decay mode is dominated by the decay into a singly charged Higgs and a real or virtual $W$-boson, giving rise to a large number of fermions in the final state. This can qualitatively alter the strategy for discovering doubly-charged scalars.

hep-ph↗

arXiv1997

Supersymmetry and Charged Current Events at HERA

A light stop, with an R-parity-violating coupling $λ'_{131}$, has been suggested as an explanation of the excess in high-$Q^2$ neutral current events observed at the HERA collider. We show that in this scheme a corresponding excess in charged current events --- such as that reported by the H1 Collaboration --- can appear naturally, without calling for the presence of light sleptons or additional R-parity-violating couplings, if there exists a chargino lighter than the stop. The predicted event shapes agree well with the data. The relevant region of parameter space is identified, taking into account constraints coming from precision electroweak measurements, atomic parity violation and recent searches for first-generation leptoquarks at the Tevatron collider.

hep-ph↗

arXiv1997

W + 1 jet to W + 0 jet Ratio at the Tevatron: A Hint of New Physics?

We interpret the reported disagreement between the measured ratio, R_{10}, of the W + 1 jet cross-section to the W + 0 jet cross-section at the Tevatron and the Standard Model (SM) prediction, as the effect of interactions mediated by a colour-octet analogue of the W-boson, the W_8. The presence of a W_8 with mass O(300) GeV, and with couplings to quarks and gluons of the order of electroweak strength, allows the observations of the D0 collaboration to be reproduced quite accurately. Such an interaction is not in contradiction with the present CDF data on W+ W- or dijet production, though higher luminosities may reveal measurable effects.

hep-ph↗

arXiv1997

R-Parity Violation at HERA ?

We examine the possibility that the high-Q^2 events seen at HERA are due to the production and decay of squarks of R-parity violating supersymmetry. The relevant R-parity violating coupling(s) is identified and shown to lie between 0.03 and 0.26. Consequences of such a coupling at other experiments, such as the LEP and Tevatron, are discussed.

hep-ph↗

arXiv1997

Like-Sign Dileptons at the Fermilab Tevatron Revisited in the Light of the HERA High-$Q^2$ Anomaly

We re-examine like-sign dilepton signals at the Fermilab Tevatron assuming that the excess high-$Q^2$ events recently seen at HERA are due to scalar resonances such as squarks of $R$-parity-violating supersymmetry. For gluinos in the mass range of 200--350 GeV, the like-sign dilepton signal can help to make the crucial distinction between the most favoured squark explanation and other proposed solutions.

hep-ph↗

arXiv1996

Light Gluino and Tevatron Data

A very light gluino ($m_{\tilde g} \lsim 2 \gev$) is still consistent with experimental data and is attractive from a theoretical standpoint. This has been shown to lead to a small gluino content of the proton. We use this effect to demonstrate that such a light gluino could lead to a striking enhancement, at Tevatron, of monojets accompanied by large missing momentum. A reanalysis of the existing data may thus rule out a light gluino for a common squark mass of upto $\sim 600 \gev$.

hep-ph↗

arXiv1996

Unravelling the $WWγ$ and $WWZ$ Vertices at the Linear Collider: $\barν νγ$ and $\barνν\bar{q}q$ final states

We perform a detailed analysis of the processes $e^+e^- \rightarrow \barν νγ$ and $\barνν\bar{q}q$ at future linear $e^+e^-$ colliders and assess their sensitivity to anomalous gauge boson couplings. We consider center of mass energies $\sqrt{s}=$ 350, 500 and 800 GeV. We demonstrate that significant improvements can be obtained if the phase space information for the cross sections is used maximally. At 800 GeV the parameters $Δκ_γ$ and $λ_γ$ can be constrained, at 95\% CL, to about 0.02 and 0.01, while the parameters $Δκ_Z$, $λ_Z$ and $Δg_1^Z$ can be probed down to about 0.009, 0.002 and 0.004 respectively. The precision of these measurements is likely to be limited by statistical errors at anticipated luminosities at these energies.

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

Light Neutral Higgs Bosons at the Low Energy $γγ$ Collider

A light neutral Higgs boson in the framework of the general two Higgs doublet model (2HDM) is not excluded by existing data. We point out that it can be looked for at the proposed low energy $γγ$ collider. Failure to detect one may lead to important limits on the parameters of the general 2HDM.

hep-ph↗