arXiv subjects
Publications and source records attributed to Uma Mahanta.
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.
In low energy phenomenology to avoid the strong constraints of proton decay it is usually assumed that light ($\approx $ 250 Gev) leptoquarks couple only to quark-lepton pairs and light diquarks couple only to quark pairs. In this paper we present two specific examples where the higgs induced mixing between leptoquarks and diquarks through trilinear interaction terms reintroduces the troublesome couplings and gives rise to proton decay. The bound on the unknown parameters of this scenario that arise from proton life time has been derived.
In this paper we use the conformal anomaly in QCD to derive the coupling of light radion to gluons in the Randall-Sundrum model and use it to compute the radion production cross section at hadron colliders by gluon fusion. We find that the radion production cross section by gluon fusion at LHC would exceed that of the higgs boson by a factor that lies between 7 and 8 over most of the range. The decay modes of the radion are similar to that of the SM higgs boson. But the striking feature is the enhancement of radion to 2-photon and radion to 2-gluon branching ratio over the SM case. Utilising this, we then discuss the possible search strategies of such scalars at Tevatron and LHC. Using the $γγ$ decay mode one can explore/exclude radion mass upto 1 TeV. Even with the current collected data at the Tevatron, one can exclude radion mass upto 120 GeV for $\vphi$= 1 TeV.
In this paper we study some low energy effects of a light stabilized radion in the Randall-Sundrum scenario. We find that the NLC 500 with its projected precision level will be able to probe the radion contribution to the anomalous magnetic moment and electric quadrupole moment of W boson for values of radion vev up to 500 Gev. On the other hand the BNL experiment E821 will be able to test the radion contribution to $a_μ$ for 1 Tev radion vev and $m_ϕ\le m_μ$. We have also shown that the higgs-radion mixing induces a 2.6% correction in the WWh coupling. Finally by comparing the radionstrahlung with the higgsstrahlung process we have found that the LEPI bound on the higgs mass based on $Z\to hl\bar{l}$ decay mode suggests a lower bound of about 35 Gev on the radion mass.
In low energy phenomenology to avoid the strong constraints of proton decay it is usually assumed that light ($\approx $ 250 Gev) leptoquarks couple only to quark-lepton pairs and light diquarks couple only to quark pairs. In this work we show that the SM Higgs boson could induce a mixing between leptoquarks and diquarks through trilinear interaction terms which reintroduces the troublesome couplings and lead to proton decay. The bound on the unknown parameters of this scenario that arise from proton life time has also been derived.
In this report we study how a light-scalar leptoquark could affect the Higgs boson production cross-section at the LHC collider. We construct the most general renormalizable and gauge invariant effective Lagrangian involving the standard model particles and a scalar, isoscalar leptoquark, η. The total cross-section for pp -> H+X is then calculated for different values of the unknown parameters λ_eta, m_eta and m_H.(Here λ_eta is the coupling associated with the Higgs-leptoquark interaction.) We find that if λ_eta is moderately large and m_eta is around a few hundred GeV, then the cross-section is significantly larger than the standard model value.
In this paper we consider the violation of supersymmetric equvalence among the R parity violating couplings $lamabda_{ijk}$ caused by widely split chiral supermultiplets. We find that if $λ^{\prime}_{2jk}=g$ and $λ^{\prime}_{1jk}=e$ then the violation of SUSY equivalence is of the order of $5-6%$ in heavy SQCD models. On the other hand if $λ^{\prime}_{3jk}=g$ and $λ_{ijk}=e$ then the violation of SUSY equivalence can be as large as 9.4% in 2-1 models.
In this work we study the effect of R parity breaking couplings on the process e^-e^-->{\tilde e}_L{\tilde e}_R. We find that an e^-e^- linear collider opearting at a center of mass energy of 500 Gev with a luminosity of 50 fb^{-1} will be able to probe the coupling [λ_{211}+λ_{311}]^{1/2} down to .045 for a bino mass of 100 Gev and selectron mass of 200 Gev. This would improve the current bound on it by a factor of 3.5. More improved bounds can be obtained from precision measurement of σ_{LR}-σ_{RR} which reduces the MSSM background.
Supersymmetry implies that the trilinear couplings between gauge bosons and gauginos are equal to all orders in perturbation theory. However if SUSY is broken and some of the superpartners have large SUSY breaking masses then they can induce non-decoupling deviations in this relation through radiative corrections. In this article we show that the deviation in the ratio of triple gauge to gaugino couplings from unity can be around 2.3% (3.3%) in heavy QCD models (2-1 models). Precision measurements of triple gaugino couplings at furture high energy colliders can therefore probe such violations and the existence of heavy superparticles in the multi Tev region which would otherwise be inaccessible.
If supersymmetry is spontaneously at a low energy scale then the resulting gravitino would be very light. The interaction strength of the longitudinal components of such a light gravitino to electron-selectron pair then becomes comparable to that of electroweak interactions. Such a light gravitino could modify the cross-section for $e^_L e^_R-->\tilde {e}_L\tilde {e}_R$ from its MSSM value. Precision measurement of this cross-section could therefore be used to probe the low energy SUSY breaking scale.
In this article we study the effect of Hg contact interaction on H production by gluon fusion at at a hadron collider. Two such d=6 operators have been considered. The present precision for measuring α_s implies a lower bound of around 2 Tev on the scale for the CP even operator O_1. On the other hand the precision for measuring d_n implies a lower bound of 10^5 TeV on the scale for the CP odd operator. We show that for the above lower bound O_1 can significantly affect the parton level cross-section for the process gg-->H.
In this article we consider the contribution of $R_p$ violating couplings to the process $e^+e^-(μ^+μ^-)\to t{\bar c}$ at high energy lepton collider. We show that the present upper bound on the relevant $R_p$ violating coulpings obtained from low energy measurements would produce a few hundred to a thousand top-charm events at the next linear $e^+e^-(μ^+μ^-)$ collider. Hence, it should be possible to observe the rare process at future lepton collider.
Tev scale new heavy physics could significantly affect the cross-section for the rare process $e^+e^-\to H\gm $ through non-renormalizable operators involving the light SM fields. In this article we show that for $\sqs =500$ Gev and $\lam =1$ Tev some of these operators, which are only weakly constrained by the latest LEP and SLD data, could produce an observable number of events for $m_H$ lying in the range 200-500 Gev. Whereas for $\lam =5$ Tev although no event with $m_H\le 250$ Gev is likely to be seen, for moderately heavy higgs bosons with $m_H$ lying in the range (400-500) Gev the production rate will be large enough to be detectable.
New interactions appearing at a scale $Λ$ larger than the weak interaction scale v can affect physical processes at energies below $Λ$ through non-renormalizable $SU(3)\times SU(2)\times U(1)_y$ invariant operators added to the standard model Lagrangian. In this article we investigate the effect of flavor conserving contact interactions on the total cross-section for the process $e^+e^-\to HZ$ at $\sqs =500$ Gev. We find that for $Λ\approx 2.5 $ Tev, which is consistent with LEP and SLD asymmetry measurements on Z peak as well as theoretical estimates, these operators can increase the total cross-section by a factor of 3 relative to the SM for intermediate mass higgs boson.
A two higgs doublet model with tree level natural flavor conservation can lead to P and T odd nucleon-nucleon (NN) interaction through tree level Feynman diagrams. In this article we estimate the magnitudes of the parameters that characterize the strength of the S-PS type of NN interaction. Stringent constraints on the parameters can be derived from the measurement of EDM's of Xe, Cs and Hg atoms in the ground state. We show that the predicted values of the parameters lie close to such constraints provided ${\absvt\over \absvo }$ is large.
In this paper we calculate the corrections to zt\bar {t} couplings induced by non-commuting ETC interactions. The extra parameters \delgbl, s^2 and {1\over x} of non-commuting ETC models and the usual SM parameters will be be assumed to be determined from a global fit to the LEP 1 EW data. We find that in the heavy (light) case F^t_L is modified by at most 4% (2.8%) relative to its SM value provided \delrb < .0088. This implies that it will be very difficult to disentangle the ETC corrections from SM corrections to zt\bar {t} vertex or to probe the effects of non-commuting ETC on zt\bar {t} couplings with the projected NLC precision of measuring them.
In standard ETC models the sideways and diagonal ETC interactions contribute to $δR_b$ with opposite signs. The aim of this article is to study the implications of the CDF value for m_t and the LEP value for R_b on $zt\bar{t}$ couplings where the LH sideways and diagonal ETC effects interfere constructively. We find that for m_t=175 Gev, $δR_b =.0022$ and m^2_s=m^2_d, F^t_v and F^t_a are modified by 19% and 7% respectively from their SM values. The constrains implied by these deviations on diagonal ETC scenarios and the feasibility of probing them at NLC through polarization and angular distribution studies in $e^+e^- \to t\bar{t}$ are also considered.
CP violating dipole moments of leptons vanish at least to three loop order and are estimated to be $({m_l\over Mev})\times 1.6\times 10^{- 40}$ e-cm in the standard model (SM), where $m_l$ is the mass of the lepton. However they can receive potentially large contributions in some beyond SM scenarios and this makes them very sensitive probes of new physics. In this article we show that a non universal interaction, involving leptoquarks to the quark-lepton pair of the third generation through helicity unsuppressed couplings of the order of ordinary gauge couplings, can generate electric and weak dipole moments of the order of $10^{-19}$ e-cm for the tau lepton. This is greater than pure supersymmetric (SUSY) and left-right (L-R) contributions by almost three orders of magnitude. It is also greater than mirror fermionic contribution by an order of magnitude. The measurements of $\dzt$ and $\dgt$ at LEP, SLC and TCF are expected to reach sensitivities of $10^{-18}$ e-cm and $10^{-19}$ e-cm respectively in near future. The observation of a non vanishing dipole moment of tau at these facilities would therefore strongly favour superstring inspired light leptoquark mediated interactions, over pure SUSY or L-R interactions and perhaps also mirror generated mixings without some sort of quark-lepton unification as its origin.