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B. Ananthanarayan

Publications and source records attributed to B. Ananthanarayan.

At least 109 records · Page 6Linked to original sources
arXiv2004

CP violation at a linear collider with transverse polarization

We show how transverse beam polarization at $e^+e^-$ colliders can provide a novel means to search for CP violation by observing the distribution of a single final-state particle without measuring its spin. We suggest an azimuthal asymmetry which singles out interference terms between standard model contribution and new-physics scalar or tensor effective interactions in the limit in which the electron mass is neglected. Such terms are inaccessible with unpolarized or longitudinally polarized beams. The asymmetry is sensitive to CP violation when the transverse polarizations of the electron and positron are in opposite senses. The sensitivity of planned future linear colliders to new-physics CP violation in $e^+e^- \to t \bar{t}$ is estimated in a model-independent parametrization. It would be possible to put a bound of $\sim 7$ TeV on the new-physics scale $Λ$ at the 90% C.L. for $\sqrt{s}=500$ GeV and $\int dt {\cal L}=500 {\rm fb}^{-1}$, with transverse polarizations of 80% and 60% for the electron and positron beams, respectively.

hep-ph↗
arXiv2004

Four-point correlator constraints on electromagnetic chiral parameters and resonance effective Lagrangians

We pursue the analysis of a set of generalized DGMLY sum rules for the electromagnetic chiral parameters at order $e^2p^2$ and discuss implications for effective Lagrangians with resonances. We exploit a formalism in which charge spurions are introduced and treated as sources. We show that no inconsistency arises from anomalies up to quadratic order in the spurions. We focus on the sum rules associated with QCD 4-point correlators which were not analyzed in detail before. Convergence properties of the sum rules are deduced from a general analysis of the form of the counterterms in the presence of electromagnetic spurions. Following the approach in which vector and axial-vector resonances are described with antisymmetric tensor fields and have a chiral order, we show that the convergence constraints are violated at chiral order four and can be satisfied by introducing a set of terms of order six. The relevant couplings get completely and uniquely determined from a set of generalized Weinberg sum-rule relations. An update on the corrections to Dashen's low-energy theorem is given.

hep-ph↗
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

Squark and slepton masses as probes of supersymmetric SO(10) unification

We carry out an analysis of the non-universal supersymmetry breaking scalar masses arising in SO(10) supersymmetric unification. By considering patterns of squark and slepton masses, we derive a set of sum rules for the sfermion masses which are independent of the manner in which SO(10) breaks to the Standard Model gauge group via its SU(5) subgroups. The phenomenology arising from such non-universality is unaffected by the symmetry breaking pattern, so long as the breaking occurs via any of the SU(5) subgroups of the SO(10) group.

hep-ph↗
arXiv2003

Review of chiral perturbation theory

A review of chiral perturbation theory and that of recent developments on the comparison of its predictions with experiment is presented. Some interesting topics with scope for further elaboration are touched upon.

hep-ph↗
arXiv2002

Sfermion Precision Measurements at a Linear Collider

At future e+- e- linear colliders, the event rates and clean signals of scalar fermion production - in particular for the scalar leptons - allow very precise measurements of their masses and couplings and the determination of their quantum numbers. Various methods are proposed for extracting these parameters from the data at the sfermion thresholds and in the continuum. At the same time, NLO radiative corrections and non-zero width effects have been calculated in order to match the experimental accuracy. The substantial mixing expected for the third generation sfermions opens up additional opportunities. Techniques are presented for determining potential CP-violating phases and for extracting tan(beta) from the stau sector, in particular at high values. The consequences of possible large mass differences in the stop and sbottom system are explored in dedicated analyses.

hep-ph↗
arXiv2002

Electromagnetic corrections in the anomaly sector

Chiral perturbation theory in the anomaly sector for $N_f=2$ is extended to include dynamical photons, thereby allowing a complete treatment of isospin breaking. A minimal set of independent chiral lagrangian terms is determined and the divergence structure is worked out. There are contributions from irreducible and also from reducible one-loop graphs, a feature of ChPT at order larger than four. The generating functional is non-anomalous at order $e^2p^4$, but not necessarily at higher order in $e^2$. Practical applications to $γπ\toππ$ and to the $π^0\to2γ$ amplitudes are considered. In the latter case, a complete discussion of the corrections beyond current algebra is presented including quark mass as well as electromagnetic effects.

hep-ph↗
arXiv2002

CP-Violation in the Production of Tau-Leptons at TESLA with Beam Polarization

We study the prospects of discovering CP-violation in the production of tau-leptons in the reaction {e+e- --> tau+tau- at TESLA, an e+e- linear collider with center-of-mass energies of 500 or even 800 GeV. Non-vanishing expectation values of certain correlations between the momenta of the decay products of the two tau leptons would signalthe presence of CP-violation beyond the standard model. We study how longitudinal beam polarization of the electron and positron beams will enhance these correlations. We find that T-odd and T-even vector correlations are well suited for the measurements of the real and imaginary parts of the electric dipole form factors. We expect measurements of the real part with a precision of roughly 10^-20 ecm and of the imaginary part of 10^-17 ecm. This compares well with the size of the expected effects in many extensions of the standard model.

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↗
arXiv2001

Reply to Comment on Infrared Fixed Point Structure in the Minimal Supersymmetric Standard Model with Baryon and Lepton Number Violation

Infrared fixed points in the minimal supersymmetric standard model with baryon and lepton number violation were studied and their structure elucidated by us in Physical Review D 63 076008 (2001). Here we reply to a comment on this paper. We emphasize that our paper concentrates on the case of the only true infrared fixed point in the model, i.e. the stable nontrivial fixed point for the top- and bottom-quark Yukawa couplings and the baryon number violating coupling. For this case the comment does not affect in any manner the numerical results and conclusions derived in our paper.

hep-ph↗
arXiv2001

$πK$ sum rules and the SU(3) chiral expansion

A recently proposed set of sum rules, based on the pion-Kaon scattering amplitudes and their crossing-symmetric conjugates are analysed in detail. A key role is played by the $l=0$ $ππ\to K\overline K$ amplitude which requires an extrapolation to be performed. It is shown how this is tightly constrained from analyticity, chiral counting and the available experimental data, and its stability is tested. A re-evaluation of the $O(p^4)$ chiral couplings $L_1$, $L_2$, $L_3$ is obtained, as well as a new evaluation of the large $N_c$ suppressed coupling $L_4$.

hep-ph↗
arXiv2001

Higgs Mass in the Standard Model from Coupling Constant Reduction

Plausible interrelations between parameters of the standard model are studied. The empirical value of the top quark mass, when used in the renormalization group equations, suggests that the ratio of the colour SU(3) gauge coupling $g_3$, and the top coupling $g_t$ is independent of the renormalization scale. On the other hand, variety of top-condensate models suggest that the Higgs self-coupling $λ$ is proportional to $g_t^2$. Invoking the requirement that the ratio $λ(t)/g_t^2(t)$ is independent of the renormalization scale $t$, fixes the Higgs mass. The pole mass of the Higgs [which differs from the renormalization group mass by a few percent] is found to be $\sim 154$ GeV for the one-loop equations and $\sim 148$ GeV for the two-loop equations.

hep-ph↗
arXiv2001

Comparison of Pion-Kaon Scattering in SU(3) Chiral Perturbation Theory and Dispersion Relations

We establish the framework for the comparison of $πK$ scattering amplitudes from SU(3) chiral perturbation theory with suitable dispersive representations which result from the combination of certain fixed-t dispersion relations with dispersion relations on hyperbolic curves. This allows for predictions for some combinations of low energy constants appearing in higher order calculations of chiral perturbation theory. Using a simple parametrization for the lowest partial waves, first estimates for some combinations are presented.

hep-ph↗
arXiv2001

Infrared Fixed Point Structure in Minimal Supersymmetric Standard Model with Baryon and Lepton Number Violation

We study in detail the renomalization group evolution of Yukawa couplings and soft supersymmetry breaking trilinear couplings in the minimal supersymmetric standard model with baryon and lepton number violation. We obtain the exact solutions of these equations in a closed form, and then depict the infrared fixed point structure of the third generation Yukawa couplings and the highest generation baryon and lepton number violating couplings. Approximate analytical solutions for these Yukawa couplings and baryon and lepton number violating couplings, and the soft supersymmetry breaking couplings are obtained in terms of their initial values at the unification scale. We then numerically study the infrared fixed surfaces of the model, and illustrate the approach to the fixed points.

hep-ph↗
arXiv2000

Roy equation analysis of pi pi scattering

We analyze the Roy equations for the lowest partial waves of elastic pi pi scattering and demonstrate that the two S-wave scattering lengths a_0^0 and a_0^2 are the essential parameters in the low energy region: Once these are known, the available experimental information determines the behaviour near threshold to within remarkably small uncertainties. An explicit numerical representation for the energy dependence of the S- and P-waves is given and it is shown that the threshold parameters of the D- and F-waves are also fixed very sharply in terms of a_0^0 and a^2_0. In agreement with earlier work, which is reviewed in some detail, we find that the Roy equations admit physically acceptable solutions only within a band of the (a_0^0,a_0^2) plane. We show that the data on the reactions e+e- -> pi pi and tau -> pi pi nu reduce the width of this band quite significantly. Furthermore, we discuss the relevance of the decay K -> pi pi e nu in restricting the allowed range of a_0^0, preparing the grounds for an analysis of the forthcoming precision data on this decay and on pionic atoms. We expect these to reduce the uncertainties in the two basic low energy parameters very substantially, so that a meaningful test of the chiral perturbation theory predictions will become possible.

hep-ph↗