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Ritesh K. Singh

Publications and source records attributed to Ritesh K. Singh.

60 records · Page 4Linked to original sources
arXiv2004

Transverse beam polarization and CP-violating triple-gauge-boson couplings in e+e- -> gamma Z

We show that an anomalous CP-violating gamma-gamma-Z vertex gives rise to a novel asymmetry with transversely polarized electron and positron beams in the process e+e- -> gamma Z. This asymmetry, which is odd under naive time reversal, is proportional to the real part of the gamma-gamma-Z CP-violating coupling. This is in contrast to the simple forward-backward asymmetry of the gamma (or Z) with unpolarized or longitudinally polarized beams studied earlier, which is even under naive time reversal, and is proportional to the imaginary part. We estimate the sensitivity of future experiments to the determination of CP-odd gamma-gamma-Z and gamma-Z-Z couplings using these asymmetries and transversely polarized beams.

hep-ph↗
arXiv2003

Axial Vector Current Matrix Elements and QCD Sum Rules

The matrix element of the isoscalar axial vector current, $\bar{u}γ_μγ_5u + \bar{d}γ_μγ_5d $, between nucleon states is computed using the external field QCD sum rule method. The external field induced correlator, $<0|\bar{q}γ_μγ_5q|0>$, is calculated from the spectrum of the isoscalar axial vector meson states. Since it is difficult to ascertain, from QCD sum rule for hyperons, the accuracy of validity of flavour SU(3) symmetry in hyperon decays when strange quark mass is taken into account, we rely on the empirical validity of Cabbibo theory to dertermine the matrix element $\bar{u}γ_μγ_5 u + \bar{d}γ_μγ_5 d - 2 \bar{s}γ_μγ_5 s$ between nucleon states. Combining with our calculation of $\bar{u}γ_μγ_5 u + \bar{d}γ_μγ_5 d$ and the well known nucleon $β$-decay constant allows us to determine $< p,s| {4/9}\bar{u}γ_μγ_5 u + {1/9}\bar{d}γ_μγ_5 d + {1/9}\bar{s}γ_μγ_5 s |p, s>$ occuring in the Bjorken sum rule. The result is in reasonable agreement with experiment. We also discuss the role of the anomaly in maintaining flavour symmetry and validity of OZI rule.

hep-ph↗
arXiv2002

Study of CP Property of the Higgs at a Photon Collider using $γγ\to t\bar t\to l X $

We study possible effects of CP violation in the Higgs sector on $t\bar t$ production at a $γγ$-collider. These studies are performed in a model-independent way in terms of six form-factors $\{\Re(S_γ), \Im(S_γ), \Re(P_γ), \Im(P_γ), S_t, P_t\}$ which parametrize the CP mixing in the Higgs sector, and a strategy for their determination is developed. We observe that the angular distribution of the decay lepton from $t/\bar t$ produced in this process is independent of any CP violation in the $tbW$ vertex and hence best suited for studying CP mixing in the Higgs sector. Analytical expressions are obtained for the angular distribution of leptons in the c.m. frame of the two colliding photons for a general polarization state of the incoming photons. We construct combined asymmetries in the initial state lepton (photon) polarization and the final state lepton charge. They involve CP even ($x$'s) and odd ($y$'s) combinations of the mixing parameters. We study limits up to which the values of $x$ and $y$, with only two of them allowed to vary at a time, can be probed by measurements of these asymmetries, using circularly polarized photons. We use the numerical values of the asymmetries predicted by various models to discriminate among them. We show that this method can be sensitive to the loop-induced CP violation in the Higgs sector in the MSSM.

hep-ph↗
arXiv2002

How Is Nature Asymmetric 2 CP and T Violation in Elementary Particle Physics

This two-part article considers certain fundamental symmetries of nature, namely the discrete symmetries of parity (P), charge conjugation (C) and time reversal (T), and their possible violation. Recent experimental results are discussed in some depth. In this second part, we discussion CP and $T$ violation and arrive at a synthesis.

physics.pop-ph↗