Debajyoti Choudhury

Signatures of an invisibly decaying Higgs particle at LHC

The Higgs particle can decay dominantly into an invisible channel in the Majoron models. We have explored the prospect of detecting such a Higgs particle at LHC via its associated production with a gluon, Z or W boson. While the signal/background ratio is too small for the first process, the latter two provide viable signatures for detecting such a Higgs particle.

Constraints on non-universal soft terms from flavor changing neutral currents

Abstract The smallness of flavor changing neutral currents constrains the soft parameter space of supersymmetric extensions of the Standard Model. These low energy constraints are translated to the soft parameter space generated at some high energy scale M gut . For gaugino masses larger than the scalar masses and non-universal A -terms the constraints are significantly diluted at M gut and do allow for the possibility of non-universal scalar masses. The strongest constraints arise in the slepton sector of the theory.

New constraints on lepton nonconserving R-parity violating couplings

Strong upper bounds are derived on certain product combinations of lepton nonconserving couplings in the minimal sypersymmetric standard model with explicit R-parity violation. The input is information from rare leptonic decays of the long-lived neutral kaon, the muon and the tau as well as from the mixings of neutral K- and B-mesons. One of these bounds is comparable and another superior to corresponding ones obtained recently from neutrinoless double beta decay.

Test of CP violating neutral gauge boson vertices in e + e - →γZ

Abstract Forward-backward asymmetry in the process e + e − → γZ proposed as a test for CP -violating anomalous γγ Z and γZZ couplings. Longitudinally polarized electron beams may be used to disentangle the effects of these couplings. We estimate possible limits that can be obtained from e + e − colliders at centre-of-mass energies of 200 GeV and 500 GeV.

Testing anomalous W couplings in e−e− collisions

Abstract We analyze the influence of anomalous gauge couplings in the reaction e−e− → e−W−νe at a 500 GeV linear collider. The limits imposed by this process on deviations from the standard model of electro-weak interaction, are competitive with those inferred from other high energy experiments. Furthermore, the allowed domain in the parameter space is quite different, and hence such an experiment would more than complement the other direct searches.

Electron-electron scattering as a probe of anomalous gauge couplings

Abstract The effect of anomalous gauge couplings on polarized e − e − scattering cross sections is examined. It turns out that different combinations of beam polarizations provide constraints which are complementary to each other and to those obtained from other experiments, such as e + e − , e − γ and γγ collisions.

Radiative B-decay as a test of CKM unitarity

Abstract We point out that R ¬ Br(b → dγ) Br(b → sγ) is a sensitive probe of possible violation of CKM unitarity. We compute R in a minimal extension of the Standard Model containing an additional isosinglet charge (− 1 3 ) quark, which leads to a deviation from CKM unitarity.

Higgs-mediated heavy neutrino pair-production at pp supercolliders

Gluon fusion into a very heavy neutrino pair by Higgs exchange is shown to lead to substantial production cross sections at

Model-independent Z' limits from electron-electron collisions

pp

Scale breaking in neutrino scattering

supercolliders even without any extra generation of quarks. Rates are calculated for scalar as well as pseudoscalar Higgs. The angular correlation between dileptons emerging from the decays of the neutrinos shows distinctive features for Dirac and Majorana neutrinos as well as for scalar and pseudoscalar Higgs.Gluon fusion into a very heavy neutrino pair by Higgs exchange is shown to lead to substantial production cross sections at pp supercolliders even without any extra generation of quarks. Rates are calculated for scalar as well as pseudoscalar Higgs. The angular correlation between dileptons emerging from the decays of the neutrinos shows distinctive features for Dirac and Majorana neutrinos as well as for scalar and pseudoscalar Higgs.