Effect Of New Physics Research Articles

Bilepton and exotic quark mass limits in 331 models fromZ→bb¯decay

We study the effect of new physics on the Z-decay into b anti-b pairs in the framework of 331 models. The decay Z -> b anti-b is computed at one loop level and, using previous results, we evaluate this branching fraction in the framework of 331 models. A wide range of the space parameter of the model is considered and possible deviations from the standard model predictions are explored. From precision measurements at the Z-pole we find the allowed region for MJ3, MX at 95 % CL.

Bounds on generic high-energy physics modifications to the primordial power spectrum from back-reaction on the metric

Modifications to the primordial power spectrum of inflationary density perturbations have been studied recently using a boundary effective field theory approach. In the approximation of a fluctuating quantum field on a fixed background, the generic effect of new physics is encoded in parameters of order H/M. Here, we point out that the back-reaction on the metric can be neglected only when these parameters obey certain bounds that may put them beyond the reach of observation.

Oscillation-enhanced search for new interaction with neutrinos

We study how well we can observe the effect of new physics in neutrino oscillation experiments.

Oscillation-enhanced search for new interaction with neutrinos

We study how well we can observe the effect of new physics in neutrino oscillation experiments.

THE DYNAMICAL MODELS AND THE $Z \rightarrow b\bar{b}$ ASYMMETRY

Motivated by the 3.2σ(1.4σ) deviations between the recent experimental value for [Formula: see text] and the standard model (SM) prediction, we examine the effect of new physics (NP) on the [Formula: see text] couplings [Formula: see text] and [Formula: see text]. First we focus our attention on the dynamical models. Then, using effective Lagrangian techniques, we discuss the corrections of NP to [Formula: see text] and [Formula: see text]. We find some kinds of NP which might explain the recently experimental data about Rb and [Formula: see text]. However, the free parameters of these kinds of NP must be severely constrained.

Baryonic rare decays ofΛb→Λl+l−

We present a systematic analysis for the rare baryonic exclusive decays of ${\ensuremath{\Lambda}}_{b}\ensuremath{\rightarrow}\ensuremath{\Lambda}{l}^{+}{l}^{\ensuremath{-}} (l=e,\ensuremath{\mu},\ensuremath{\tau}).$ We study the differential decay rates and the dilepton forward-backward, lepton polarization, and various $\mathrm{CP}$ asymmetries with a new simple set of form factors inspired by the heavy quark effective theory. We show that most of the observables are insensitive to the nonperturbative QCD effects. To illustrate the effect of new physics, we discuss our results in an explicit supersymmetric extension of the standard model, which contains new $\mathrm{CP}$ violating phases and therefore induces sizable $\mathrm{CP}$ violating asymmetries.

Implications of LEP and SLD data for new physics inZbb¯couplings

The combined LEP/SLD data on the b\bar b forward-backward asymmetry from the Z-pole measurements may imply the presence of new physics in the $Zb\bar b$ couplings. In general, the effect of new physics can be parameterized by $SU_C(3)\times SU_L(2)\times U_Y(1)$ invariant higher dimensional operators. By fitting the recently announced LEP/SLD data on A_b and R_b, the size of the coupling strengths of these operators can be determined. We also found that the new physics operators can be divided into two types, depending on their Higgs field content. The ones involving the Higgs have very mild effects at higher energy colliders, while the other type which do not contain the Higgs field can show significantly large effects on $b\bar b$ production at LEP II, $t\bar t$ production at the NLC and single top production at the Tevatron. The preliminary data from the LEP II measurements disfavors the second type of operators.

Further study of CP violation and branching ratios for and in the standard model and beyond

In this work we study the CP violation for and up to leading and next-to-leading order QCD corrections in the standard model, two-Higgs-doublet model and the minimal supersymmetric extension of the standard model. We also study the effect of new physics on the branching ratios of these two decay modes. We find that within the parameter space constrained by the observation of the decay , new physics does not affect the CP asymmetries greatly, and the prediction of new physics to the branching ratios of and is the same as that of the standard model up to a minor discrepancy as far as the Yukama coupling constants are perturbative.

QED logarithms in the electroweak corrections to the muon anomalous magnetic moment

We employ an effective Lagrangian approach to derive the leading-logarithm two-loop electroweak contributions to the muon anomalous magnetic moment, a_mu. We show that these corrections can be obtained using known results on the anomalous dimensions of composite operators. We confirm the result of Czarnecki et al. for the bosonic part and present the complete sin^2 \theta_W dependence of the fermionic contribution. The approach is then used to compute the leading-logarithm three-loop electroweak contribution to a_mu. Finally we derive, in a fairly model-independent way, the QED improvement of new-physics contributions to a_mu and to the electric dipole moment (EDM) of the electron. We find that the QED corrections reduce the effect of new physics at the electroweak scale by 6% (for a_mu) and by 11% (for the electron EDM).

Towards isolation of new physics in ${B^0_s}$ - ${\bar{B}^0_s}$ mixing

In many extensions of the standard model, new physics is possible to contribute significantly to \(B^0_s\)-\(\bar{B}^0_s\) mixing. We show that the effect of new physics, both its phase information and its magnitude, can be isolated from measurements of \(CP\) asymmetries in the semileptonic \(B_s\) transitions and in some nonleptonic \(B_s\) decays into hadronic \(CP\) eigenstates. We also find that the rates of \(CP\)-forbidden decays at the \(\Upsilon (5S)\) resonance are not suppressed by the large \(B_s\) mass difference, thus they can be used to extract the \(CP\)-violating phase of new physics in either \(B^0_s\)-\(\bar{B}^0_s\) or \(K^0\)-\(\bar{K}^0\) mixing.

Towards isolation of new physics in

In many extensions of the standard model, new physics is possible to contribute significantly to B^0_s-\bar{B}^0_s mixing. We show that the effect of new physics, both its phase information and its magnitude, can be isolated from measurements of CP asymmetries in the semileptonic B_s transitions and in some nonleptonic B_s decays into hadronic CP eigenstates. We also find that the rates of CP-forbidden decays at the \Upsilon (5S) resonance are not suppressed by the large B_s mass difference, thus they can be used to extract the CP-violating phase of new physics in either B^0_s-\bar{B}^0_s or K^0-\bar{K}^0 mixing.

Bb¯production on theZresonance and implications for CERN LEP 2

In terms of an effective Lagrangian, we examine the effect of new physics associated with third-generation fermions on $b\overline{b}$ production at the $Z$ resonance and study its implications for CERN LEP2. We obtain the constraints on such operators with derivative couplings at LEP1 and the SLC, and determine the prospects for detecting their presence at LEP2. We find that despite the small observed deviations from the standard model on the $Z$ resonance, much larger deviations from standard model predictions are possible at LEP2, and the corresponding couplings can be determined rather precisely.

The effect of new physics on [formula omitted

Motivated by the ∼ 2σ discrepancy between the experimental value for R b and the theoretical prediction of the Standard Model, we examine the effect of new physics on the Z-b- b vertex. Using general results for both new scalars and gauge bosons, we show that two conditions must be satisfied in order for new physics to give observable deviations in the vertex. In particular, the fermion in the loop must transform chirally under SU(2) × U(1) and it must be massive compared to the exchanged boson. We examine the implications of these results on the 2 Higgs Doublet model and the Left-Right Symmetric model.