41 research outputs found
The gradient flow running coupling with twisted boundary conditions
We study the gradient flow for Yang-Mills theories with twisted boundary
conditions. The perturbative behavior of the energy density is used to define a running coupling at a scale given by the
linear size of the finite volume box. We compute the non-perturbative running
of the pure gauge coupling constant and conclude that the technique is
well suited for further applications due to the relatively mild cutoff effects
of the step scaling function and the high numerical precision that can be
achieved in lattice simulations. We also comment on the inclusion of matter
fields.Comment: 27 pages. LaTe
Covariant Description of Flavor Conversion in the LHC Era
A simple covariant formalism to describe flavor and CP violation in the
left-handed quark sector in a model independent way is provided. The
introduction of a covariant basis, which makes the standard model approximate
symmetry structure manifest, leads to a physical and transparent picture of
flavor conversion processes. Our method is particularly useful to derive robust
bounds on models with arbitrary mechanisms of alignment. Known constraints on
flavor violation in the K and D systems are reproduced in a straightforward
manner. Assumptions-free limits, based on top flavor violation at the LHC, are
then obtained. In the absence of signal, with 100 fb^{-1} of data, the LHC will
exclude weakly coupled (strongly coupled) new physics up to a scale of 0.6 TeV
(7.6 TeV), while at present no general constraint can be set related to Delta
t=1 processes. LHC data will constrain Delta F=2 contributions via same-sign
tops signal, with a model independent exclusion region of 0.08 TeV (1.0 TeV).
However, in this case, stronger bounds are found from the study of CP violation
in D-bar D mixing with a scale of 0.57 TeV (7.2 TeV). In addition, we apply our
analysis to models of supersymmetry and warped extra dimension. The minimal
flavor violation framework is also discussed, where the formalism allows to
distinguish between the linear and generic non-linear limits within this class
of models.Comment: 24 pages, 6 figures. Some corrections and clarifications; references
added. Matches published versio
Strange and charm HVP contributions to the muon (g â 2) including QED corrections with twisted-mass fermions
The hadronic vacuum polarization contribution to the muon g â 2 from lattice QCD
We present a calculation of the hadronic vacuum polarization contribution to
the muon anomalous magnetic moment, , in lattice QCD
employing dynamical up and down quarks. We focus on controlling the infrared
regime of the vacuum polarization function. To this end we employ several
complementary approaches, including Pad\'e fits, time moments and the
time-momentum representation. We correct our results for finite-volume effects
by combining the Gounaris-Sakurai parameterization of the timelike pion form
factor with the L\"uscher formalism. On a subset of our ensembles we have
derived an upper bound on the magnitude of quark-disconnected diagrams and
found that they decrease the estimate for by at most 2%.
Our final result is , where the first error is statistical, and the second denotes the
combined systematic uncertainty. Based on our findings we discuss the prospects
for determining with sub-percent precision.Comment: 42 pages, 7 figures, version published in JHE
Charged-Higgs phenomenology in the Aligned two-Higgs-doublet model
The alignment in flavour space of the Yukawa matrices of a general
two-Higgs-doublet model results in the absence of tree-level flavour-changing
neutral currents. In addition to the usual fermion masses and mixings, the
aligned Yukawa structure only contains three complex parameters, which are
potential new sources of CP violation. For particular values of these three
parameters all known specific implementations of the model based on discrete
Z_2 symmetries are recovered. One of the most distinctive features of the
two-Higgs-doublet model is the presence of a charged scalar. In this work, we
discuss its main phenomenological consequences in flavour-changing processes at
low energies and derive the corresponding constraints on the parameters of the
aligned two-Higgs-doublet model.Comment: 46 pages, 19 figures. Version accepted for publication in JHEP.
References added. Discussion slightly extended. Conclusions unchange
Heavy-light mesons in the epsilon-regime
We study the finite-size scaling of heavy-light mesons in the static limit.
We compute two-point functions of chiral current densities as well as
pseudoscalar densities in the epsilon-regime of heavy meson Chiral Perturbation
Theory (HMChPT). As expected, finite volume dependence turns out to be
significant in this regime and can be predicted in the effective theory in
terms of the infinite-volume low-energy couplings. These results might be
relevant for extraction of heavy-meson properties from lattice simulations.Comment: 32 pages, 4 figure
Isospin breaking corrections to meson masses and the hadronic vacuum polarization: a comparative study
We calculate the strong isospin breaking and QED corrections to meson masses
and the hadronic vacuum polarization in an exploratory study on a
lattice with an inverse lattice spacing of GeV and
an isospin symmetric pion mass of MeV. We include QED in an
electro-quenched setup using two different methods, a stochastic and a
perturbative approach. We find that the electromagnetic correction to the
leading hadronic contribution to the anomalous magnetic moment of the muon is
smaller than for the up quark and for the strange quark, although
it should be noted that this is obtained using unphysical light quark masses.
In addition to the results themselves, we compare the precision which can be
reached for the same computational cost using each method. Such a comparison is
also made for the meson electromagnetic mass-splittings.Comment: 49 pages, 20 figure