121 research outputs found
Massive scalar field evolution in de Sitter
The behaviour of a massive, non-interacting and non-minimally coupled
quantised scalar field in an expanding de Sitter background is investigated by
solving the field evolution for an arbitrary initial state. In this approach
there is no need to choose a vacuum in order to provide a definition for
particle states. We conclude that the expanding de Sitter space is a stable
equilibrium configuration under small perturbations of the initial conditions.
Depending on the initial state, the energy density can approach its asymptotic
value from above or below, the latter of which implies a violation of the weak
energy condition. The backreaction of the quantum corrections can therefore
lead to a phase of super-acceleration also in the non-interacting massive case.Comment: 22 pages, 5 figures. v2: References added. v3: Expanded text, added
references. Version accepted by JHE
Standard Model vacuum decay with gravity
We present a calculation of the decay rate of the electroweak vacuum, fully
including all gravitational effects and a possible non-minimal Higgs-curvature
coupling , and using the three-loop Standard Model effective potential.
Without a non-minimal coupling, we find that the effect of the gravitational
backreaction is small and less significant than previous calculations
suggested. The gravitational effects are smallest, and almost completely
suppressed, near the conformal value of the non-minimal coupling.
Moving away from this value in either direction universally suppresses
the decay rate.Comment: 23 pages, 7 figure
Lattice calculation of non-Gaussianity from preheating
If light scalar fields are present at the end of inflation, their
non-equilibrium dynamics such as parametric resonance or a phase transition can
produce non-Gaussian density perturbations. We show how these perturbations can
be calculated using non-linear lattice field theory simulations and the
separate universe approximation. In the massless preheating model, we find that
some parameter values are excluded while others lead to acceptable but
observable levels of non-Gaussianity. This shows that preheating can be an
important factor in assessing the viability of inflationary models.Comment: 4 pages, 1 figure; erratum adde
Higgs-curvature coupling and post-inflationary vacuum instability
We study the post-inflationary dynamics of the Standard Model (SM) Higgs
field in the presence of a non-minimal coupling to gravity, both
with and without the electroweak gauge fields coupled to the Higgs. We assume a
minimal scenario in which inflation and reheating are caused by chaotic
inflation with a quadratic potential, and no additional new physics is relevant
below the Planck scale. By using classical real-time lattice simulations with a
renormalisation group improved effective Higgs potential and by demanding the
stability of the Higgs vacuum after inflation, we obtain upper bounds for
, taking into account the experimental uncertainty of the top-Yukawa
coupling. We compare the bounds in the absence and presence of the electroweak
gauge bosons, and conclude that the addition of gauge interactions has a rather
minimal impact. In the unstable cases, we parametrize the time when such
instability develops. For a top-quark mass , the
Higgs vacuum instability is triggered for , although a
slightly lower mass of pushes up this limit to
. This, together with the estimation
for stability during inflation, provides tight constraints to the
Higgs-curvature coupling within the SM.Comment: 15 pages, 13 figures. Minor changes to match version published in PR
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