arXiv subjects

Javier Virto

Publications and source records attributed to Javier Virto.

66 records · Page 4Linked to original sources

arXiv2009

Exact NLO strong interaction corrections to the Delta F=2 effective Hamiltonian in the MSSM

We compute the order alpha_s^3 (next-to-leading) corrections to the Wilson coefficients of the Delta F=2 effective Hamiltonian in the Minimal Supersymmetric Standard Model with completely arbitrary soft terms. These results are relevant for phenomenological studies of neutral meson mixings in the presence of large squark mass splittings, in particular in hierarchical scenarios of supersymmetry. These corrections achieve a considerable reduction of the uncertainty related to the matching scale ambiguity, and are therefore numerically relevant. We briefly analyze the effect of certain mass splittings on the size of the NLO corrections, and compare it with the case of almost degenerate squarks in the mass insertion approximation.

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arXiv2009

NLO corrections to the Delta F=2 Hamiltonian in the MSSM with non-degenerate squarks

We present the next-to-leading strong interaction corrections to the Delta F=2 Hamiltonian in the MSSM with exact diagonalization of the squark mass matrices. These results allow phenomenological studies of neutral meson mixing in scenarios with non-degenerate squarks, with control over the renormalization scale and scheme dependence.

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arXiv2008

Pade Unitarizations: A Critical Look

We use the Linear Sigma Model to test the convergence of different sequences of Pade Approximants when used to unitarize the low energy pi-pi scattering amplitude. We find that, in this particular case, diagonal sequences reproduce the sigma pole with high accuracy, as opposed to other sequences that have been discussed extensively.

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arXiv2008

Some Remarks on the Pade Unitarization of Low-Energy Amplitudes

We present a critical analysis of Pade-based methods for the unitarization of low energy amplitudes. We show that the use of certain Pade Approximants to describe the resonance region may lead to inaccurate determinations. In particular, we find that in the Linear Sigma Model the unitarization of the low energy amplitude through the inverse amplitude method produces essentially incorrect results for the mass and width of the sigma. Alternative sequences of Pades are studied and we find that the diagonal sequences (i.e., [N/N]) have much better convergence properties.

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arXiv2008

Sum rules for B-->pi eta('), K eta('), eta(') eta(') decays

We provide a set of sum rules, using flavour symmetries, relating CP-averaged ratios and CP asymmetries of different neutral and charged B mesons decaying into an eta(') particle together with a pion, a kaon or a second eta('). These sume rules allow us to give a prediction for the B^0-->K^0 eta branching ratio. We also predict a clear sign anti-correlation between the two B^0-->pi^0 (eta,eta') CP-asymmetries, and find a combined constraint on the branching ratios and CP-asymmetries of the three B-->eta(')eta(') decay modes.

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arXiv2007

Topics in Hadronic B Decays

We discuss some topics concerning exclusive non-leptonic B decays. In particular we focus on Bs->KK decays, for which we present complementary predictions within the SM, as well as the impact that SUSY would have on the CP observables. We also present an analysis of Bs->VV decays that allows to measure the mixing angle of the Bs system. We make special emphasis on the control of hadronic uncertainties.

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arXiv2007

Penguin-mediated B_(d,s)->VV decays and the Bs - anti-Bs mixing angle

In this letter, we propose three different strategies to extract the weak mixing angle phi_s of the Bs system using penguin-mediated decays into vectors, mainly Bs->K*K*, Bs->phi K* and Bs->phi phi. We also provide predictions for the longitudinal branching ratio and CP-asymmetries of Bs->K*K* using a method that combines QCD factorisation with flavour symmetries to relate this decay to its Bd counterpart.

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arXiv2007

Evading 1/m_b-suppressed IR divergencies in QCDF: Bs-->KK Decays and B_{d,s} mixing

We analyze the deviations of the mixing induced CP asymmetry in B-->phi Ks from sin(2beta), as well as the deviations of the asymmetries in Bs-->K*K*, Bs-->phi K* and Bs-->phi phi from sin(2beta_s), that arise in SM due to penguin pollution. We use a theoretical input which is short-distance dominated in QCD-factorization and thus free of IR-divergencies. We also provide alternative ways to extract angles of the unitarity triangle from penguin-mediated decays, and give predictions for Bs-->K*K* observables.

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arXiv2006

Bs-->K+K- and Bs-->K0 anti-K0 Decays within Supersymmetry

We compute the supersymmetric (SUSY) contributions to the observables in Bs-->K+K- and Bs-->K0 anti-K0 decays. The hadronic parameters in the standard-model (SM) amplitudes are obtained from the Bd-->K0 anti-K0 decay using a recent approach that combines flavor SU(3) symmetry and a controlled input from QCD factorization. The latest experimental data for BR(Bs-->K+K-) is in agreement with the SM prediction. We study how the branching ratios and the direct and mixing-induced CP asymmetries of both Bs-->KK decay modes are affected with the inclusion of SUSY, after imposing constraints from BR(B--> Xs gamma), B--> pi K and Delta Ms over the parameter space. While the branching ratios remain unaffected by SUSY, we identify the CP asymmetries of the Bs-->KK decays as the most promising observables to look for large deviations from the SM.

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arXiv2006

Exploring B_{d,s}-> KK decays through flavour symmetries and QCD-factorisation

We present a new analysis of B_{d,s}->KK modes within the SM, relating them in a controlled way through SU(3)-flavour symmetry and QCD-improved factorisation. We propose a set of sum rules for B_{d,s}-> K^0{\bar K}^0 observables. We determine B_s-> KK branching ratios and CP-asymmetries as functions of A_{dir}(B_d-> K^0{\bar K}^0), pointing out a conflict between BR(B_s-> K+K-) in the SM and data. Finally, we predict the amount of U-spin breaking between B_d-> pi+pi- and B_s-> K+K-.

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arXiv2006

Supersymmetric Contributions to Bs->K+K-

Inspired by the existing calculation of B->piK decays in supersymmetry (SUSY), we evaluate the dominant SUSY contributions to Bs->K+K-. We show that the observables of this process can be significantly modified in the presence of SUSY. In particular, the branching ratio can be increased considerably compared to the prediction of the standard model (SM). The effect is even more dramatic for the CP-violating asymmetries A_dir and A_mix. These asymmetries, expected to be small in the SM (A_dir is predicted to take only positive values), change drastically with SUSY contributions. The measurement of these observables can therefore be used to detect the presence of physics beyond the SM, and put constraints on its parameters.

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arXiv2005

Bd^0(t)->pi^+pi^- and Bs^0(t)-> K^+ K^- Decays: A Tool to Measure New-Physics Parameters

If physics beyond the standard model is present in B decays, experimental measurements seem to suggest that it principally affects those processes with significant b->s penguin amplitudes. It was recently argued that, in general, such new-physics (NP) effects can be parametrized in terms of a single NP amplitude A^q and phase Φ_q, for q=u,d,s,c. In this paper, we show that the study of the decays Bs(t) -> K^+ K^- and Bd(t) -> π^+π^- allows one to measure the NP parameters A^u and Φ_u. We examine the implications for this method of the latest experimental results on these decays. If NP is found in Bs(t) -> K^+ K^-, it can be partially identified through measurements of Bs(t)-> K^0 \bar K^0.

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