394 research outputs found
Constraining New Physics with D meson decays
Latest Lattice results on form factors evaluation from first principles
show that the standard model (SM) branching ratios prediction for the leptonic
decays and the semileptonic SM branching ratios of the
and meson decays are in good agreement with the world average
experimental measurements. It is possible to disprove New Physics hypothesis or
find bounds over several models beyond the SM. Using the observed leptonic and
semileptonic branching ratios for the D meson decays, we performed a combined
analysis to constrain non standard interactions which mediate the transition. This is done either by a model independent way through
the corresponding Wilson coefficients or in a model dependent way by finding
the respective bounds over the relevant parameters for some models beyond the
standard model. In particular, we obtain bounds for the Two Higgs Doublet Model
Type-II and Type III, the Left-Right model, the Minimal Supersymmetric Standard
Model with explicit R-Parity violation and Leptoquarks. Finally, we estimate
the transverse polarization of the lepton in the decay and we found it
can be as high as .Comment: 28 pages, 8 figures, 3 tables. Improved and extended analysis with
updated form factors from Lattice QC
CP violation in semileptonic tau lepton decays
The leading order contribution to the direct CP asymmetry in tau^{+/-} ->
K^{+/-} pi^0 nu_{tau} decay rates is evaluated within the Standard Model. The
weak phase required for CP violation is introduced through an interesting
mechanism involving second order weak interactions, which is also responsible
for tiny violations of the Delta S= Delta Q rule in K_{l3} decays. The
calculated CP asymmetry turns out to be of order 10^{-12}, leaving a large
window for studying effects of non-standard sources of CP violation in this
observable.Comment: 5 pages, 3 figures, version published in Phys.Rev.
Complex Hybrid Inflation and Baryogenesis
We propose a hybrid inflation model with a complex waterfall field which
contains an interaction term that breaks the U(1) global symmetry associated to
the waterfall field charge. We show that the asymmetric evolution of the real
and imaginary parts of the complex field during the phase transition at the end
of inflation translates into a charge asymmetry. The latter strongly depends on
the vev of the waterfall field, which is well constrained by diverse
cosmological observations.Comment: 4 RevTex pages, no figures. Changes made in response to referee's
comments; matches version published in Phys.Rev.Let
Neutrino mass determination from a four-zero texture mass matrix
We analyze the different parametrizations of a general four-zero texture mass
matrices for quarks and leptons, that are able to reproduce the CKM and PMNS
mixing matrices. This study is done through a Chi-Square analysis. In quark
sector, only four solutions are found to be compatible with CKM mixing matrix.
In leptonic sector, using the last experimental results about the mixing angles
in the neutrino sector, our Chi-Square analysis shows a preferred value for
m_nu_3 to be around 0.05 eV independently of the parametrization of the
four-zero texture mass matrices chosen for the charged leptons and neutrinos.Comment: 9 pages, 3 figures, 2 tables. Accepted for publication in Physical
Review
Neutrino Spin Flavor Precession and Leptogenesis
We argue that \Delta L=2 neutrino spin flavor precession, induced by the
primordial magnetic fields, could have a significant impact on the leptogenesis
process that accounts for the baryon asymmetry of the universe. Although the
extra galactic magnetic fields is extremely weak at present time (about 10^{-9}
Gauss), the primordial magnetic filed at the electroweak scale could be quite
strong (of order 10^{17} Gauss). Therefore, at this scale, the effects of the
spin flavor precession are not negligible. We show that the lepton asymmetry
may be reduced by 50% due to the spin flavor precession. In addition, the
leptogenesis will have different feature from the standard scenario of
leptogenesis, where the lepton asymmetry continues to oscillate even after the
electroweak phase transition.Comment: 5 pages, one figure. References adde
Annihilation contribution and decays
We analyze the decays and
and show that within the factorization approximation a phenomenological
consistent picture can be obtained. We show that in this approach the
operator provides the dominant contributions to the suppressed channel . When the is considered a two quark state, evaluation of the
annihilation form factor using Perturbative implies that this
contribution is not negligible, and furthermore it can interfere constructively
or destructively with other penguin contributions. As a consequence of this
ambiguity, the positive identification of can not
distinguish between the two or four quark assignment of the . According to
our calculation, a best candidate to distinguish the nature of scalar is
since the predictions for a four quark model is one
order of magnitude smaller than for the two quark assignment. When the scalars
are seen as two quarks states, simple theoretical assumptions based on SU(2)
isospin symmetry provide relations between different B decays involving one
scalar and one pseudoscalar meson.Comment: 12 pages, 3 figure
A Consistent Scenario for B to PS Decays
We consider B to PS decays where P stands for pseudoscalar and S for a heavy
(~1500 MeV) scalar meson. We achieve agreement with available experimental data
-- which includes a two orders of magnitude hierarchy -- assuming the scalars
mesons are two quark states. The contribution of the dipolar penguin operator
O_{11} is quantified.Comment: 10 pages, no figure
Supersymmetric contributions to and decays in SCET
We study the decay modes and using Soft Collinear Effective Theory. Within Standard Model and
including the error due to the SU(3) breaking effect in the SCET parameters we
find that BR and BR
corresponding to
solution 1 and solution 2 of the SCET parameters respectively.For the decay
mode , we find that BR and BR corresponding to solution 1 and
solution 2 of the SCET parameters respectively. We extend our study to include
supersymmetric models with non-universal A-terms where the dominant
contributions arise from diagrams mediated by gluino and chargino exchanges. We
show that gluino contributions can not lead to an enhancement of the branching
ratios of and . In
addition, we show that SUSY contributions mediated by chargino exchange can
enhance the branching ratio of by about 14% with
respect to the SM prediction. For the branching ratio of , we find that SUSY contributions can enhance its value by about 1% with
respect to the SM prediction.Comment: 25 pages,5 figures, version accepted for publicatio
Properties of the massive Thirring model from the XYZ spin chain
We consider here the massive Thirring model regularized with the XYZ spin
chain. We numerically calculate the mass ratios of particles which lie in the
discrete part of the spectrum and obtain results in accordance with the DHN
formula and in disagreement with recent calculations in the literature based on
the numerical Bethe ansatz and infinite momentum frame methods. We also analyze
the short distance behavior of these states and evaluate the conformal
dimensions. This paper, taken together with the previous one for the
sine-Gordon model, confirms the duality relation between two models formulated
by Klassen and Melzer [Int. J. Mod. Phys. A 8, 4131 (1993)].Comment: 11 pages, 6 figures, to be published in Phys. Rev. D 6
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