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Uma Mahanta

Publications and source records attributed to Uma Mahanta.

At least 19 recordsLinked to original sources
arXiv2003

Updated Collider Bounds on the Parameters of Dynamical Torsion

We constrain the parameters of dynamical torsion, namely, the torsion-fermion coupling and the torsion mass, by making a careful analysis of current LEP-2 data at several energies, as well as CDF and D0 data from Run-I of the Tevatron. We find that measurements of the forward-backward asymmetry in the e+- e- -> mu+- mu- channel at LEP-2 produce the most restrictive bounds over most of the parameter space,though other measurements, too, have a significant role to play. Our results considerably improve the existing constraints on models with dynamical torsion.

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arXiv2003

The effect of a light radion on the triviality bound on higgs mass

In this paper we study how the triviality bound on higgs mass in the context of the SM is modified by a light stabilized radion of the Goldberger-Wise variety. Our approach is inherently perturbative. Including the radion contribution to $\bt(ł)$ and $\bt(g_t)$ to one loop we evolve the higgs self coupling $ł$ from the cut off $Ł(=\vphi)$ down to the EW scale $μ_0 = v$. The triviality bound is obtained by requiring that $ł(Ł) = \sqrt{4 π}$ which is the perturbative limit. We also study the effect of small changes in the UVBC on the triviality bound both in the presence and absence of a light radion.

hep-ph↗
arXiv2002

Torsion contraints from the recent precision measurement of the muon anomaly

In this paper we consider non-minimal couplings of the Standard Model fermions to the vector (trace) and axial vector (pseudo-trace) components of the torsion tensor. We then evaluate the contributions of these vector and axial vector components to the muon anomaly and use the recent precision measurement of the muon anomaly to derive constraints on the torsion parameters.

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arXiv2002

Testable $(g - 2)_μ$ contribution due to a light stabilized radion in the Randall-Sundrum model

In this paper we calculate the $(g-2)_μ$ contribution due to a light stabilized radion using the radion couplings both to the kinetic energy and the mass term of the muon. We find that the $(g-2)_μ$ contribution due to radion diverges logarithmically with the cut off. We then show that the bound from precision EW data on radion phenomenology allows a sizable shift in the radion mediated muon anomaly that could be detected or tested with the present precision and certainly with the future precision for measuring muon anomaly.

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arXiv2002

$ρ$ parameter constraints on radion phenomenology and a lower bound on Higgs mass

In this paper we determine the contribution of a light stabilized radion to the weak isospin violating $ρ$ parameter by using an ultraviolet momentum cut off as the regulator. The LEP1 bound on $ρ^{new}$ is then used to derive constraints on the radion mass $\mphi$ and its vev $\vphi$. Finally by using the beta function of the higgs self coupling we have determined a lower bound on the higgs mass from the rho parameter constraints on $\mphi$ and $\vphi$. Our results show that for $\mphi <$ 600 GeV the rho parameter bound on $m_h$ is stronger than the present direct bound from LEPII.

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arXiv2002

Tadpole diagrams due to KK modes of graviton and radion do not contribute to the $ρ$ parameter

In this brief report we show that tadpole diagrams due to KK modes of the graviton and radion do not contribute to the vectorial isospin breaking $ρ$ parameter. Our result is fairly general and it holds both for ADD and RS type scenarios. It shows that the difference between the results of different publications on this subject is not due to some of them not having considered tadpole diagrams in estimating the contribution to the $ρ$ parameter.

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arXiv2001

Constraints on radion vev from the beta functions for top yukawa coupling and higgs self coupling in the Randall-Sundrum model

In this paper we determine how the beta function for the top Yukawa coupling to one loop is modified by a light stabilized radion in the Randall-Sundrum model. We then use this beta function together with β(λ) to deteremine lower bounds on the radion vev <ϕ> for different values of λ(m_z) and m_ϕ by demanding that both g_t(μ) and λ(μ) should remain perturbative from m_z up ot the cut off Λ. We find that the lower bounds on <ϕ> that follow from the condition λ(Λ)<\sqrt{4π} nearly agree with those that follow from g_t(Λ)<\sqrt{4π}. We have also determined the critical value of <ϕ> for different values of λ(m_z) and m_ϕ from the line of fixed points which is given by β(g_t)=0.

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arXiv2001

Implications of BNL measurement of δa_μ on scalar leptoquark mass and coupling

Recently BNL have measured the muon magnetic moment anomaly with increased precision. The world average experimental value at present shows a discrepancy of 43(16)\times 10^{-10} from the Standard Model value. In this paper we investigate the implications of this difference on a class of scalar leptoquark interactions to SM quark-lepton pair. We find that for leptoquarks in the few hundred Gev range the BNL muon anomaly could arise from leptoquark couplings that are much smaller than the electromagnetic coupling. We also find that the BNL value for the muon anomaly leads to an unambiguous prediction for the electric dipole moment of the muon and a bound on the flavor changing leptoquark coupling relevant for the rare decay μ\to eγ.

hep-ph↗
arXiv2001

Constraining new physics in the Tev range by the recent BNL measurement of (g-2)_μ

In this paper we study the implications of the recent high precision measurement of (g-2)_μ by BNL on new heavy physics beyond the SM in a model independent way. We find that if the new physics responsible for the muon anomaly is due to d=6 direct operators then they could arise from the following follwing three broad classes of new physics a) new particles in the few hundred Gev range with weak gauge coupling b) strongly interacting particles and resonances in the few Tev range and c) massive Kaluza-Klein modes of the graviton in the Tev range with couplings to SM particles of the order of ${E\over (Tev)}$.

hep-ph↗
arXiv2001

Implication of a light radion on the RG evolution of higgs self coupling in the Randall-Sundrum model

In this paper we determine how the beta funtion of the higgs self coupling λat one loop order is modified by a light stabilized radion in the Randall-Sundrum model. We then use the modified beta function to derive a lower bound on the radion vev <ϕ>, both for perturbative and non-perturbative values of λat the ultra violet cut off Λ. The lower bound on <ϕ> is obtained by demanding that the renormalized coupling λ(μ) at μ=100 GeV be consistent with the present experimental bound of 110 GeV on the higgs mass from LEP2 searches. We also show that if λ(Λ) is sufficiently small then an upper bound on <ϕ> can be determined by requiring that β(λ)be positive over the relevant momentum range.

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arXiv2000

A quasi unitarity bound on the radion mass in the Randall-Sundrum model

In this paper we derive a quasi unitarity bound on the radion mass ($\mphi$) from the process $hh\to ϕϕ$. We find that at sufficiently high energies (i.e. when $ s\gg m_h^2, \mphi^2 $) the J=0 partial wave amplitude for the above process violates unitarity if $\mphi^2 > m_h^2+16 π\vphi^2 $. Combining this result with the unitarity bound $m_h^2<{16πv\vphi\over 3}$ obtained from the process $hh\to hϕ$ we get an upper bound of $4\sqrt π\vphi [1+{v\over 3 \vphi}]^{1\over 2}$ on the radion mass. This bound is however valid only in the low energy effective theory where we can ignore the effects of the gravitational KK modes and the string/M theoretic excitations.

hep-ph↗
arXiv2000

Quantum effects of compactified AdS_5 geometry on the higgs potential

In this paper we determine the one loop radiative correction to the higgs potential due to quantum fluctuations about the background metric of Randall-Sundrum model. We then examine the effects of the one loop effective potential on the stability of the classical vacuum paying particular attention to the tadpole terms which could dominate over the classical potential for small field configurations. We find that although the one loop potential due to scale fluctuations could develop a tadpole term in certain regions of the parameter space, it is positive for either sign of H. The quadratic and quartic terms in the radiative correction are too small to cause any instability to the classical vacuum for field configurations that do not violate the limits of ordinary perturbation theory.

hep-ph↗
arXiv2000

Implications of radion-higgs couplings for high energy scattering in the Randall-Sundrum model

In this report we derive the couplings of the Randall-Sundrum radion to the standard model higgs boson. We then use these couplings to determine the J=0 partial wave amplitude for the process $hh\to hϕ$. We find that at very high energies (i.e. $s\gg m_h^2, \mp^2$) the s wave partial wave unitarity is violated if $m_h>m_c\approx \sqrt{16π\vphi v}$ where $\vphi$ is the radion vev. Interestingly this bound is independent of the radion mass to the leading order. We also consider the high energy behaviour of the transition amplitudes for some other processes in the RS scenario and compare them with their SM behaviour.

hep-ph↗
arXiv2000

New Physics, precision electroweak data and an upper bound on higgs mass

In this paper we express the effect of new physics on gauge boson self energy corrections through non-renormalizable dimension six operators. Using the precision electroweak data we then determine a lower bound on the scale $ł$ associated with the underlying new physics. The lower bound on $ł$ is then used to derive an upper bound on $m_h$ through the triviality relation.

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arXiv2000

Effects of non-factorizable metric on neutrino oscillation inside supernova

In this paper we construct the interaction potential between the dense supernova core and neutrinos due to the exchange of light radions in the Randall-Sundrum scenario. We then show that the radion exchange potential affects the neutrino oscillation phenomenology inside the supernova significantly if the radion mass is less than around 1 GeV. In order that the Bethe-Wilson mechanism for heating the envelope and r-process neucleosynthesis be operative, the radion mass must be greater than 1 GeV. Bounds on the radion mass of the same order of magnitude can also be derived from TASSO and CLEO data on B decays.

hep-ph↗
arXiv2000

Radion stabilization in the Randall-Sundrum model with qudratic and quartic potentials

In this report we investigate the Goldberger-Wise (GW) mechanism of radion stabilization with quartic potential on the hidden brane and quadratic potential on the visible brane. The advantage of our simplified scenario over the original GW mechanism is that the modulus potential can be evaluated for finite $\lv$ and $\lh$. This enables us to probe how the modulus potential behaves over the entire range of $\lh$. By staying away from the GW limit of ${k \over \lv v_v^2} \to $0 and ${k \over \lh v_h^2}\to $0 we show that it is possible to choose the parameters of the model so that the potential exhibits a minimum at $k\rc \approx$ 12 and this adjustment does not involve any extreme fine tuning of parameters.

hep-ph↗
arXiv2000

Neutrino masses and mixing angles from leptoquark interactions

In this paper we show that the mixing between leptoquarks (LQ's) from different $SU(2)_l$ multiplets can generate a non-trivial Majorana mass matrix for neutrinos through one loop self energy diagrams. Such mixing can arise from gauge invariant and renormalizable LQ-Higgs interaction terms after EW symmetry breaking. We use the experimental indication on neutrino oscillation to find constraints on specific combinations of LQ couplings to quark-lepton pairs and to the SM higgs boson. These constraints are compared with the ones from $π\to e\bar ν_e$.

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