16,236 research outputs found
Higgs-Yukawa model on the lattice
We present results from two projects on lattice calculations for the
Higgs-Yukawa model. First we report progress on the search of first-order
thermal phase transitions in the presence of a dimension-six operator, with the
choices of bare couplings that lead to viable phenomenological predictions. In
this project the simulations are performed using overlap fermions to implement
the required chiral symmetry. Secondly, our study for applying finite-size
scaling techniques near the Gaussian fixed point of the Higgs-Yukawa model is
presented. We discuss the analytical formulae for the Higgs Yukawa model and
show results for a first numerical study in the pure scalar sector of
the theory.Comment: 8 pages, 4 figures; Contribution to the proceedings of the 35th
International Symposium on Lattice Field Theory, 18 - 24 June 2017, Granada,
Spai
The Yang-Mills gradient flow and SU(3) gauge theory with 12 massless fundamental fermions in a colour-twisted box
We perform the step-scaling investigation of the running coupling constant,
using the gradient-flow scheme, in SU(3) gauge theory with twelve massless
fermions in the fundamental representation. The Wilson plaquette gauge action
and massless unimproved staggered fermions are used in the simulations. Our
lattice data are prepared at high accuracy, such that the statistical error for
the renormalised coupling, g_GF, is at the subpercentage level. To investigate
the reliability of the continuum extrapolation, we employ two different lattice
discretisations to obtain g_GF. For our simulation setting, the corresponding
gauge-field averaging radius in the gradient flow has to be almost half of the
lattice size, in order to have this extrapolation under control. We can
determine the renormalisation group evolution of the coupling up to g^2_GF ~ 6,
before the onset of the bulk phase structure. In this infrared regime, the
running of the coupling is significantly slower than the two-loop perturbative
prediction, although we cannot draw definite conclusion regarding possible
infrared conformality of this theory. Furthermore, we comment on the issue
regarding the continuum extrapolation near an infrared fixed point. In addition
to adopting the fit ansatz a'la Symanzik for performing this task, we discuss a
possible alternative procedure inspired by properties derived from low-energy
scale invariance at strong coupling. Based on this procedure, we propose a
finite-size scaling method for the renormalised coupling as a means to search
for infrared fixed point. Using this method, it can be shown that the behaviour
of the theory around g^2_GF ~ 6 is still not governed by possible infrared
conformality.Comment: 24 pages, 6 figures; Published version; Appendix A added for
tabulating data; One reference included; Typos correcte
A lattice study of a chirally invariant Higgs-Yukawa model including a higher dimensional -term
We discuss the non-thermal phase structure of a chirally invariant
Higgs-Yukawa model on the lattice in the presence of a higher dimensional
-term. For the exploration of the phase diagram we use analytical,
lattice perturbative calculations of the constraint effectice potential as well
as numerical simulations. We also present first results of the effects of the
-term on the lower Higgs boson mass bounds
Lattice study of infrared behaviour in SU(3) gauge theory with twelve massless flavours
We present details of a lattice study of infrared behaviour in SU(3) gauge
theory with twelve massless fermions in the fundamental representation. Using
the step-scaling method, we compute the coupling constant in this theory over a
large range of scale. The renormalisation scheme in this work is defined by the
ratio of Polyakov loops in the directions with different boundary conditions.
We closely examine systematic effects, and find that they are dominated by
errors arising from the continuum extrapolation. Our investigation suggests
that SU(3) gauge theory with twelve flavours contains an infrared fixed point.Comment: 29 pages, 15 figures, 4 tables. Minor revision. Published versio
Deep-inelastic scattering and the operator product expansion in lattice QCD
We discuss the determination of deep-inelastic hadron structure in lattice
QCD. By using a fictitious heavy quark, direct calculations of the Compton
scattering tensor can be performed in Euclidean space that allow the extraction
of the moments of structure functions. This overcomes issues of operator mixing
and renormalisation that have so far prohibited lattice computations of higher
moments. This approach is especially suitable for the study of the twist-two
contributions to isovector quark distributions, which is practical with current
computing resources. While we focus on the isovector unpolarised distribution,
our method is equally applicable to other quark distributions and to
generalised parton distributions. By looking at matrix elements such as
(where and are vector
and axial-vector heavy-light currents) within the same formalism, moments of
meson distribution amplitudes can also be extracted.Comment: 10 pages, 5 figures, version accepted for publicatio
Stabilizing the electroweak vacuum by higher dimensional operators in a Higgs-Yukawa model
The Higgs boson discovery at the LHC with a mass of approximately 126 GeV
suggests, that the electroweak vacuum of the standard model may be metastable
at very high energies. However, any new physics beyond the standard model can
change this picture. We want to address this important question within a
lattice Higgs-Yukawa model as the limit of the standard model (SM). In this
framework we will probe the effect of a higher dimensional operator for which
we take a -term. Such a term could easily originate as
a remnant of physics beyond the SM at very large scales.
As a first step we investigate the phase diagram of the model including such
a operator. Exploratory results suggest the existence
of regions in parameter space where first order transitions turn to second
order ones, indicating the existence of a tri-critical line. We will explore
the phase structure and the consequences for the stability of the SM, both
analytically by investigating the constraint effective potential in lattice
perturbation theory, and by studying the system non-perturbatively using
lattice simulations.Comment: 7 pages, 6 figures; Proceedings of the 31st International Symposium
on Lattice Field Theory - LATTICE 201
Heavy meson chiral perturbation theory in finite volume
We present the first step towards the estimation of finite volume effects in
heavy-light meson systems using heavy meson chiral perturbation theory. We
demonstrate that these effects can be amplified in both light-quark and
heavy-quark mass extrapolations (interpolations) in lattice calculations. As an
explicit example, we perform a one-loop calculation for the neutral B meson
mixing system and show that finite volume effects, which can be comparable with
currently quoted errors, are not negligible in both quenched and partially
quenched QCD.Comment: Talk presented at Lattice2004(heavy), Fermilab, June 21st-26th, 2004.
Three pages, two figure
Matrix elements of the complete set of \Delta B = 2 and \Delta C = 2 operators in heavy meson chiral perturbation theory
Using heavy meson chiral perturbation theory, we consider the light
quark-mass and spatial volume dependence of the matrix elements of \Delta B=2
and \Delta C=2 four-quark operators relevant for
B^{0}_{(s)}{-}\bar{B}^{0}_{(s)} and D^{0}{-}\bar{D}^{0} mixing, and the B_{s}
meson width difference. Our results for these matrix elements are obtained in
the N_{f}=2+1 partially quenched theory, which becomes full QCD in the limit
where sea and valence quark masses become equal. They can be used in
extrapolation of lattice calculations of these matrix elements to the physical
light quark masses and to infinite volume. An important conclusion of this
paper is that the chiral extrapolations for matrix elements of heavy-light
meson mixing beyond the Standard Model, and those relevant for the B_s width
difference are more complicated than that for the Standard Model mixing matrix
elements.Comment: 13 pages; version accepted for publicatio
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