360 research outputs found
Phase structure and Higgs boson mass in a Higgs-Yukawa model with a dimension-6 operator
We investigate the impact of a term included in a
chirally invariant lattice Higgs-Yukawa model. Such a term could emerge from
BSM physics at some larger energy scale. We map out the phase structure of the
Higgs-Yukawa model with positive and negative quartic self coupling
of the scalar fields. To this end, we evaluate the constraint effective
potential in lattice perturbation theory and also determine the magnetization
of the model via numerical simulations which allow us to reach also
non-perturbative values of the couplings. As a result, we find a complex phase
structure with first and second order phase transitions identified through the
magnetization. Further we analyze the effect of such a term on the
lower Higgs boson mass bound to see, whether the standard model lower mass
bound can be altered.Comment: proceedings for The 32nd International Symposium on Lattice Field
Theor
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
Higgs boson mass bounds in the presence of a heavy fourth quark family
We present Higgs boson mass bounds in a lattice regularization allowing thus
for non-perturbative investigations. In particular, we employ a lattice
modified chiral invariant Higgs-Yukawa model using the overlap operator. We
show results for the upper and lower Higgs boson mass bounds in the presence of
a heavy mass-degenerate quark doublet with masses ranging up to 700 GeV. We
perform infinite volume extrapolations in most cases, and examine several
values of the lattice cutoff. Furthermore, we argue that the lower Higgs boson
mass bound is stable with respect to the addition of higher dimensional
operators to the scalar field potential. Our results have severe consequences
for the phenomenology of a fourth generation of quarks if a light Higgs boson
is discovered at the LHC
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
Constraining a fourth generation of quarks: non-perturbative Higgs boson mass bounds
We present a non-perturbative determination of the upper and lower Higgs
boson mass bounds with a heavy fourth generation of quarks from numerical
lattice computations in a chirally symmetric Higgs-Yukawa model. We find that
the upper bound only moderately rises with the quark mass while the lower bound
increases significantly, providing additional constraints on the existence of a
straight-forward fourth quark generation. We examine the stability of the lower
bound under the addition of a higher dimensional operator to the scalar field
potential using perturbation theory, demonstrating that it is not significantly
altered for small values of the coupling of this operator. For a Higgs boson
mass of we find that the maximum value of the fourth
generation quark mass is , which is already in conflict
with bounds from direct searches.Comment: 6 pages, 2 figure
The phase structure of a chirally invariant lattice Higgs-Yukawa model - numerical simulations
The phase diagram of a chirally invariant lattice Higgs-Yukawa model is
explored by means of numerical simulations. The results revealing a rich phase
structure are compared to analytical large Nf calculations which we performed
earlier. The analytical and numerical results are in excellent agreement at
large values of Nf. In the opposite case the large Nf computation still gives a
good qualitative description of the phase diagram. In particular we find
numerical evidence for the predicted ferrimagnetic phase at intermediate values
of the Yukawa coupling constant and for the symmetric phase at strong Yukawa
couplings. Emphasis is put on the finite size effects which can hide the
existence of the latter symmetric phase.Comment: 14 pages, 11 figure
Fermion-Higgs model with strong Wilson-Yukawa coupling in two dimensions
The fermion mass spectrum is studied in the quenched approximation in the
strong coupling vortex phase (VXS) of a globally U(1)U(1)
symmetric scalar-fermion model in two dimensions. In this phase fermion
doublers can be completely removed from the physical spectrum by means of a
strong Wilson-Yukawa coupling. The lowest lying fermion spectrum in this phase
consists most probably only of a massive Dirac fermion which has charge zero
with respect to the group. We give evidence that the fermion which is
charged with respect to that subgroup is absent in the VXS phase. When the
gauge fields are turned on, the neutral fermion may couple chirally to
the massive vector boson state in the confinement phase. The outcome is very
similar to our findings in the strong coupling symmetric phase (PMS) of
fermion-Higgs models with Wilson-Yukawa coupling in four dimensions, with the
exception that in four dimensions the neutral fermion does most probably
decouple from the bosonic bound states.Comment: 21 pages, 6 postscript figures (appended), Amsterdam ITFA 92-21, HLRZ
J\"ulich 92-5
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