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B. Ananthanarayan

Publications and source records attributed to B. Ananthanarayan.

At least 73 records · Page 4Linked to original sources
arXiv2012

The $Dπ$ form factors from analyticity and unitarity

We study the shape parameters of the $Dπ$ scalar and vector form factors using as input dispersion relations and unitarity for the moments of suitable heavy-light correlators evaluated with Operator Product Expansions, including $O(α_s^2)$ terms in perturbative QCD. For the scalar form factor, a low energy theorem and phase information on the unitarity cut are implemented to further constrain the shape parameters. We finally determine points on the real axis and isolate regions in the complex energy plane where zeros of the form factors are excluded.

hep-ph↗
arXiv2012

Probing strongly interacting W's at the ILC with polarized beams

We study the possibility of fingerprinting a strongly interacting $W$ boson sector which is consistent with present day LHC searches at the ILC with longitudinal as well as transversely polarized electron and positron beams. We account for the final state interaction using a suitable Omnès formalism in terms of a plausible resonance description, and carry out thorough analyses of cross sections, asymmetries and angular distributions of the $W's$. We carry out a comparison with other extensions of the Standard Model, where heavy additional $Z'$ bosons arise naturally. We also consider the effect of the strong final state interaction on a correlation that depends on $(ϕ_--ϕ_+)$, where the $ϕ_\mp$ are the azimuthal angles of decay leptons, and find that it is a useful discriminant.

hep-ph↗
arXiv2012

Isolating CP-violating γZZ coupling in e+e- \to γZ with transverse beam polarizations

We revisit the process $e^+e^- \to γZ$ at the ILC with transverse beam polarization in the presence of anomalous CP-violating $γZ Z$ coupling $λ_1$ and $γγZ$ coupling $λ_2$. We point out that if the final-state spins are resolved, then it becomes possible to fingerprint the anomalous coupling {\rm Re}$λ_1$.90% confidence level limit on {\rm Re}$λ_1$ achievable at ILC with center-of-mass energy of 500 GeV or 800 GeV with realistic initial beam polarization and integrated luminosity is of the order of few times of $10^{-2}$ when the helicity of $Z$ is used and $10^{-3}$ when the helicity of $γ$ is used. The resulting corrections at quadratic order to the cross section and its influence on these limits are also evaluated and are shown to be small. The benefits of such polarization programmes at the ILC are compared and contrasted for the process at hand. We also discuss possible methods by which one can isolate events with a definite helicity for one of the final-state particles.

hep-ph↗
arXiv2011

Constraining the properties of K_{l3} form factors with analyticity and unitarity

Bounds on the shape parameters of K_{l3} form factors are investigated in a general model independent framework. Using the method of unitarity bounds for correlators evaluated in pQCD, chiral symmetry and experimental information on the phase and modulus of πK form factors up to an energy t_{in}=1 GeV^2, we constrain the shape parameters of the scalar and vector form factors, the value of the scalar form factor at t=M_π^2-M_K^2, and exclude regions where zeros can exist on the real energy line and in the complex energy plane.

hep-ph↗
arXiv2011

Implications of unitarity and analyticity for the Dπform factors

We consider the vector and scalar form factors of the charm-changing current responsible for the semileptonic decay D\rightarrow πl ν. Using as input dispersion relations and unitarity for the moments of suitable heavy-light correlators evaluated with Operator Product Expansions, including O(α_s^2) terms in perturbative QCD, we constrain the shape parameters of the form factors and find exclusion regions for zeros on the real axis and in the complex plane. For the scalar form factor, a low energy theorem and phase information on the unitarity cut are also implemented to further constrain the shape parameters. We finally propose new analytic expressions for the $Dπ$ form factors, derive constraints on the relevant coefficients from unitarity and analyticity, and briefly discuss the usefulness of the new parametrizations for describing semileptonic data.

hep-ph↗
arXiv2011

Implications of the recent high statistics determination of the pion electromagnetic form factor in the timelike region

The recently evaluated two-pion contribution to the muon g-2 and the phase of the pion electromagnetic form factor in the elastic region, known from ππscattering by Fermi-Watson theorem, are exploited by analytic techniques for finding correlations between the coefficients of the Taylor expansion at t=0 and the values of the form factor at several points in the spacelike region. We do not use specific parametrizations and the results are fully independent of the unknown phase in the inelastic region. Using for instance, from recent determinations, = (0.435 \pm 0.005) fm^2 and F(-1.6 GeV^2)=0.243^{+0.022}_{-0.014}, we obtain the allowed ranges 3.75 GeV^{-4}\lesssim c \lesssim 3.98 GeV^{-4} and 9.91 GeV^{-6}\lesssim d \lesssim 10.46 GeV^{-6} for the curvature and the next Taylor coefficient, with a strong correlation between them. We also predict a large region in the complex plane where the form factor can not have zeros.

hep-ph↗
arXiv2011

Signals of additional Z boson in e+e-\to W+W^- at the ILC with polarized beams

We consider the possibility of fingerprinting the presence of heavy additional Z' bosons that arise naturally in extensions of the standard model such as E_6 models and left-right symmetric models, through their mixing with the standard model Z boson. By considering a class of observables including total cross sections, energy distributions and angular distributions of decay leptons we find significant deviation from the standard model predictions for these quantities with right-handed electrons and left-handed positrons at \sqrt{s}=800 GeV. The deviations being less pronounced at smaller centre of mass energies as the models are already tightly constrained. Our work suggests that the ILC should have a strong beam polarization physics program particularly with these configurations. On the other hand, a forward backward asymmetry and lepton fraction in the backward direction are more sensitive to new physics with realistic polarization due to interesting interplay with the neutrino t- channel diagram. This process complements the study of fermion pair production processes that have been considered for discrimination between these models.

hep-ph↗
arXiv2010

Top-spin analysis of new scalar and tensor interactions in e^+ e^- collisions with beam polarization

We utilize top polarization in the process e+ e-\rightarrow t\bar{t} at the ILC with transverse beam polarization to probe interactions of the scalar and tensor type beyond the standard model and to disentangle their individual contributions. 90% confidence level limits on the interactions with realistic integrated luminosity are presented and are found to improve by an order of magnitude compared to the case when the spin of the top quark is not measured. Sensitivities of the order of a few times 10^{-3} TeV^{-2} for real and imaginary parts of both scalar and tensor couplings at \sqrt{s}=500 and 800 GeV with an integrated luminosity of 500 fb^{-1} and completely polarized beams is shown to be possible. A powerful model-independent framework for inclusive measurements is employed to describe the spin-momentum correlations and their C, P and T properties is presented in a technical appendix.

hep-ph↗
arXiv2010

Improving the phenomenology of K_{l3} form factors with analyticity and unitarity

The shape of the vector and scalar K_{l3} form factors is investigated by exploiting analyticity and unitarity in a model-independent formalism. The method uses as input dispersion relations for certain correlators computed in perturbative QCD in the deep Euclidean region, soft-meson theorems, and experimental information on the phase and modulus of the form factors along the elastic part of the unitarity cut. We derive constraints on the coefficients of the parameterizations valid in the semileptonic range and on the truncation error. The method also predicts low-energy domains in the complex $t$-plane where zeros of the form factors are excluded. The results are useful for K_{l3} data analyses and provide theoretical underpinning for recent phenomenological dispersive representations for the form factors.

hep-ph↗
arXiv2010

Theory of unitarity bounds and low energy form factors

We present a general formalism for deriving bounds on the shape parameters of the weak and electromagnetic form factors using as input correlators calculated from perturbative QCD, and exploiting analyticity and unitarity. The values resulting from the symmetries of QCD at low energies or from lattice calculations at special points inside the analyticity domain can beincluded in an exact way. We write down the general solution of the corresponding Meiman problem for an arbitrary number of interior constraints and the integral equations that allow one to include the phase of the form factor along a part of the unitarity cut. A formalism that includes the phase and some information on the modulus along a part of the cut is also given. For illustration we present constraints on the slope and curvature of the K_l3 scalar form factor and discuss our findings in some detail. The techniques are useful for checking the consistency of various inputs and for controlling the parameterizations of the form factors entering precision predictions in flavor physics.

hep-ph↗
arXiv2010

Stringent constraints on the scalar K pi form factor from analyticity, unitarity and low-energy theorems

We investigate the scalar K pi form factor at low energies by the method of unitarity bounds adapted so as to include information on the phase and modulus along the elastic region of the unitarity cut. Using at input the values of the form factor at t=0 and the Callan-Treiman point, we obtain stringent constraints on the slope and curvature parameters of the Taylor expansion at the origin. Also, we predict a quite narrow range for the higher order ChPT corrections at the second Callan-Treiman point.

hep-ph↗
arXiv2009

W physics at the ILC with polarized beams as a probe of the Littlest Higgs Model

We study the possibility of using W pair production and leptonic decay of one of the W's at the ILC with polarized beams as a probe of the Littlest Higgs Model. We consider cross-sections, polarization fractions of the W's, leptonic decay energy and angular distributions, and left-right polarization asymmetry as probes of the model. With parameter values allowed by present experimental constraints detectable effects on these observables at typical ILC energies of 500 GeV and 800 GeV will be present. Beam polarization is further found to enhance the sensitivity.

hep-ph↗
arXiv2009

Improved bounds on the radius and curvature of the K pi scalar form factor and implications to low-energy theorems

We obtain stringent bounds in the < r^2 >_S^{K pi}-c plane where these are the scalar radius and the curvature parameters of the scalar pi K form factor respectively using analyticity and dispersion relation constraints, the knowledge of the form factor from the well-known Callan-Treiman point m_K^2-m_pi^2, as well as at m_pi^2-m_K^2 which we call the second Callan-Treiman point. The central values of these parameters from a recent determination are accomodated in the allowed region provided the higher loop corrections to the value of the form factor at the second Callan-Treiman point reduce the one-loop result by about 3% with F_K/F_pi=1.21. Such a variation in magnitude at the second Callan-Treiman point yields 0.12 fm^2 \lesssim < r^2>_S^{K pi} \lesssim 0.21 fm^2 and 0.56 GeV^{-4} \lesssim c \lesssim 1.47 GeV^{-4} and a strong correlation between them. A smaller value of F_K/F_pi shifts both bounds to lower values.

hep-ph↗
arXiv2009

New constraints on the Pion EM form factor using Pi'(-Q^2)

We study the constraints arising on the expansion parameters c and d of the Pion electromagnetic form factor from the inclusion of pure space-like data and the phase of time-like data along with one space-like datum, using as input the first derivative of the QCD polarization amplitude Pi'(-Q^2). These constraints when combined with other analyses, provide a valuable check on a determination of c due to Guo et al. and on our previous work where pionic contribution to the (g-2) of the muon was used as the input. This work further illustrates the power of analyticity techniques in form factor analysis.

hep-ph↗
arXiv2008

Constraining the low energy Pion electromagnetic form factor with space-like and phase of time-like data

The Taylor coefficients c and d of the Pion EM form factor are constrained using analyticity, knowledge of the phase of the form factor in the time-like region, 4 m_pi^2 \le t \le \tin and its value at one space-like point, using as input the (g-2) of the muon. This is achieved using the technique of Lagrange multipliers, that gives a transparent expression for the corresponding bounds. We present a detailed study of the sensitivity of the bounds to the choice of time-like phase and errors present in the space-like data, taken from recent experiments. We find that our results constrain c stringently. We compare our results with those in literature and find agreement with the chiral perturbation theory results for $c$. We obtain d \sim O(10)GeV^{-6} when c is set to the chiral perturbation theory values.

hep-ph↗
arXiv2008

A note on the heat kernel coefficients for nonminimal operators

We consider certain results for the heat kernel of nonminimal operators. The general expressions provided by Gusynin and Kornyak resulting from symbolic computation programmes for n dimensions are evaluated for 4 dimensions which are checked against results given by Barvinsky and Vilkovisky. We also check that the results in flat space are consistent with earlier results of Guendelmen et al. We then consider a powerful construction of the Green function of a nonminimal operator by Shore for covariantly constantly gauge fields in flat spacetime, and employ dimensional arguments to produce a check on the gauge parameter dependence of a certain coefficient. The connection of the results for heat kernel coefficients emanating from the construction of Shore, to those from other techniques is hereby established for the first time.

hep-th↗
arXiv2008

Two-particle kinematic distributions from new physics at an electron-positron collider with polarized beams

The kinematic distributions in two-particle inclusive processes at an e+e- collider arising from standard-model s-channel exchange of a virtual gamma or Z and the interference of the standard-model contribution with contributions from physics beyond the standard model involving s-channel exchanges are derived entirely in terms of the space-time signature of such new physics. Transverse as well as longitudinal polarizations of the electron and positron beams are taken into account. We show how these model-independent distributions can be used to deduce some general properties of the nature of the interaction. We then specialize to two specific two-particle final states, viz., ZH, where H is one of the Higgs bosons in a model with an extended Higgs sector, and f fbar, where f, fbar are a pair of conjugate charged fermions, wherein distributions of two (of the possibly several) decay products are measured. We show how some of the properties of the distributions have been realized in the analysis of physics beyond the standard model in earlier work which made use of two-particle angular distributions.

hep-ph↗