114 research outputs found
Time dependence in decays
We discuss the theory and phenomenology of
decays in the presence of neutral-meson mixing. We derive expressions for the
time-dependent angular distributions for decays into CP eigenstates, and
identify the relevant observables that can be extracted from time-integrated
and time-dependent analyses with or without tagging, with a focus on the
difference between measurements at -factories and hadronic machines. We
construct two observables of interest, which we call and , and
which are theoretically clean at large recoil. We compute these two observables
in the Standard Model, and show that they have good potential for New Physics
searches by considering their sensitivity to benchmark New Physics scenarios
consistent with current data. These results apply to decays
such as ,
and .Comment: 39 pages, 3 figures. Typos corrected. Matches published versio
Non-minimal model for Lepton Flavour Universality Violation in decays
331 models constitute an extension of the Standard Model (SM) obtained by
enlarging the SM gauge group
to the group . We investigate
how a non-minimal 331 model may embed lepton flavour universality violating
contributions to processes without introducing lepton flavour
violation, as suggested by the recent LHCb measurements of the ratios and
. We discuss the model-independent scenarios of New Physics in currently favoured by the data that could be accommodated by this
model and consider a few phenomenological constraints on this model.Comment: 24 pages, 3 figures, 2 tables. Accepted for publication in Phys. Rev.
Isospin breaking in pion and form factors
Isospin breaking in the form factors induced by the difference
between charged and neutral pion masses is discussed within a framework built
on suitably subtracted dispersion representations. The form
factors are constructed in an iterative way up to two loops in the low-energy
expansion by implementing analyticity, crossing, and unitarity due to two-meson
intermediate states. Analytical expressions for the phases of the two-loop form
factors of the channel are presented, allowing
one to connect the difference of form-factor phase shifts measured
experimentally (out of the isospin limit) and the difference of - and
-wave phase shifts studied theoretically (in the isospin limit).
The dependence with respect to the two -wave scattering lengths and
in the isospin limit is worked out in a general way, in contrast to
previous analyses based on one-loop chiral perturbation theory. The results on
the phases of the form factors obtained by the
NA48/2 collaboration at the CERN SPS are reanalysed including isospin-breaking
correction to extract values for the scattering lengths and .Comment: 15 pages, 3 figures, prepared for the proceedings of the XIth
Confinement and Hadron Spectrum Conference, Saint-Petersburg, Sept. 8-12,
201
Short-distance QCD corrections to mixing at next-to-leading order in Left-Right models
Left-Right (LR) models are extensions of the Standard Model where left-right
symmetry is restored at high energies, and which are strongly constrained by
kaon mixing described in the framework of the effective
Hamiltonian. We consider the short-distance QCD corrections to this Hamiltonian
both in the Standard Model (SM) and in LR models. The leading logarithms
occurring in these short-distance corrections can be resummed within a
rigourous Effective Field Theory (EFT) approach integrating out heavy degrees
of freedom progressively, or using an approximate simpler method of regions
identifying the ranges of loop momentum generating large logarithms in the
relevant two-loop diagrams. We compare the two approaches in the SM at
next-to-leading order, finding a very good agreement when one scale dominates
the problem, but only a fair agreement in the presence of a large logarithm at
leading order. We compute the short-distance QCD corrections for LR models at
next-to-leading order using the method of regions, and we compare the results
with the EFT approach for the box with two charm quarks (together with
additional diagrams forming a gauge-invariant combination), where a large
logarithm occurs already at leading order. We conclude by providing
next-to-leading-order estimates for , and boxes in LR models.Comment: Accepted for publication in JHE
An analysis of B_{d,s} mixing angles in presence of New Physics and an update of Bs -> K0* anti-K0*
We discuss a simple approach to measure the weak mixing angles phi_s and
phi_d of the Bs and Bd systems in the presence of New Physics. We present a new
expression that allows one to measure directly the New Physics mixing angles if
New Physics contributes significantly to the mixing only. We apply the method
to specific penguin-mediated B->PP, B->PV and B ->VV modes. We provide a very
stringent and simple bound on the direct CP asymmetries of all these modes, the
violation of which is a signal of New Physics in decay. Within the same
theoretical framework, an updated prediction for the branching ratio of Bs->K0*
anti-K0* is presented, which can be compared with a recent LHCb analysis.Comment: 11 pages, 3 figure
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