929 research outputs found
Higher-order scalar interactions and SM vacuum stability
Investigation of the structure of the Standard Model effective potential at
very large field strengths opens a window towards new phenomena and can reveal
properties of the UV completion of the SM. The map of the lifetimes of the
vacua of the SM enhanced by nonrenormalizable scalar couplings has been
compiled to show how new interactions modify stability of the electroweak
vacuum. Whereas it is possible to stabilize the SM by adding Planck scale
suppressed interactions and taking into account running of the new couplings,
the generic effect is shortening the lifetime and hence further destabilisation
of the SM electroweak vacuum. These findings have been illustrated with phase
diagrams of modified SM-like models. It has been demonstrated that
stabilisation can be achieved by lowering the suppression scale of higher order
operators while picking up such combinations of new couplings, which do not
deepen the new minima of the potential. Our results show the dependence of the
lifetime of the electroweak minimum on the magnitude of the new couplings,
including cases with very small couplings (which means very large effective
suppression scale) and couplings vastly different in magnitude (which
corresponds to two different suppression scales).Comment: plain Latex, 9 figure
Features of electroweak symmetry breaking in five dimensional SUSY models
We explore the phenomenological predictions of a supersymmetric standard
model, with a large extra dimension and unifying gauge couplings. The modified
five dimensional renormalisation group equations make it possible to obtain
light, maximally mixed stops, with a low scale of supersymmetry breaking and a
low unification scale. This allows the fine-tuning to be lowered right down to
the barrier coming directly from experimental lower limits on the stop masses.
We also show that attempts at modifying the SUSY breaking pattern to obtain
more natural soft terms at the high scale do not give the expected fine-tuning
relaxation, and only RGE effects turn out to be effective in generating a lower
fine-tuning
The impact of non-minimally coupled gravity on vacuum stability
We consider vacuum decay in the presence of a non-minimal coupling to
gravity. We extend the usual thin-wall solution to include the non-minimal
coupling. We also perform a full numerical study and discuss the validity of
the new thin-wall approximation. Implications of a large cosmological constant,
whose influence on the geometry boosts the tunnelling rate, are discussed. Our
results show that the influence of the non-minimal coupling differs
significantly between the cases of Minkowski and deSitter backgrounds. In the
latter the decay probability quickly decreases when the coupling grows and in
fact the vacuum can be made absolutely stable simply due to introduction of the
non-minimal coupling. In the case of Minkowski background the effect is much
weaker and the decay rate even increases for small values of the non-minimal
coupling
Higgs domain walls in the thermal background
Most cosmological models predict that the universe was hot and dense at the
early stages of it's evolution. In this paper we analyse the influence of the
thermal bath of Standard Model particles on the dynamics of cosmological Higgs
domain walls. This manuscript poses an~extension of our earlier work in which
we investigated the evolution of networks of Higgs domain walls neglecting the
impact of temperature variation.
Using the thermally corrected effective potential of Standard Model we have
found that both the position of the local maximum separating minima
and the width of domain walls strongly depend on temperature . For
temperatures higher than they respectively increase
proportionally and decrease inverse proportionally to the increasing
temperature. Thus, the energy scale of the problem follows the value of
temperature.
Our numerical lattice simulations based on the PRS algorithm reveal that
Higgs domain walls in the presence of the background thermal bath are highly
unstable and decay shortly after formation. Moreover we have found that the
fraction of horizons produced by inflation in which Higgs field expectation
value is higher then needs to be very low in order for the evolution
of the~network of the domain walls to end in the electroweak vacuum. This means
that Higgs domain walls necessarily were very rare objects and their average
energy density was very small. As a result, the domain walls can not
significantly effect cosmological observables
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