513 research outputs found
Vector-like Fields, Messenger Mixing and the Higgs mass in Gauge Mediation
In order to generate, in the context of gauge mediation, a Higgs mass around
126 GeV that avoids the little hierarchy problem, we explore a set of models
where the messengers are directly coupled to new vector-like fields at the TeV
scale in addition to the usual low energy degrees of freedom. We find that in
this context, stop masses lighter than 2 TeV and large -terms are generated,
thereby improving issues of fine tuning.Comment: 17 pages. V3: Version accepted for publication at JHE
Fluctuations of large-scale jets in the stochastic 2D Euler equation
Two-dimensional turbulence in a rectangular domain self-organises into
large-scale unidirectional jets. While several results are present to
characterize the mean jets velocity profile, much less is known about the
fluctuations. We study jets dynamics in the stochastically forced
two-dimensional Euler equations. In the limit where the average jets velocity
profile evolves slowly with respect to turbulent fluctuations, we employ a
multi-scale (kinetic theory) approach, which relates jet dynamics to the
statistics of Reynolds stresses. We study analytically the Gaussian
fluctuations of Reynolds stresses and predict the spatial structure of the jets
velocity covariance. Our results agree qualitatively well with direct numerical
simulations, clearly showing that the jets velocity profile are enhanced away
from the stationary points of the average velocity profile. A numerical test of
our predictions at quantitative level seems out of reach at the present day
Kinetic theory of jet dynamics in the stochastic barotropic and 2D Navier-Stokes equations
We discuss the dynamics of zonal (or unidirectional) jets for barotropic
flows forced by Gaussian stochastic fields with white in time correlation
functions. This problem contains the stochastic dynamics of 2D Navier-Stokes
equation as a special case. We consider the limit of weak forces and
dissipation, when there is a time scale separation between the inertial time
scale (fast) and the spin-up or spin-down time (large) needed to reach an
average energy balance. In this limit, we show that an adiabatic reduction (or
stochastic averaging) of the dynamics can be performed. We then obtain a
kinetic equation that describes the slow evolution of zonal jets over a very
long time scale, where the effect of non-zonal turbulence has been integrated
out. The main theoretical difficulty, achieved in this work, is to analyze the
stationary distribution of a Lyapunov equation that describes quasi-Gaussian
fluctuations around each zonal jet, in the inertial limit. This is necessary to
prove that there is no ultraviolet divergence at leading order in such a way
that the asymptotic expansion is self-consistent. We obtain at leading order a
Fokker--Planck equation, associated to a stochastic kinetic equation, that
describes the slow jet dynamics. Its deterministic part is related to well
known phenomenological theories (for instance Stochastic Structural Stability
Theory) and to quasi-linear approximations, whereas the stochastic part allows
to go beyond the computation of the most probable zonal jet. We argue that the
effect of the stochastic part may be of huge importance when, as for instance
in the proximity of phase transitions, more than one attractor of the dynamics
is present
A Singlet Extension of the MSSM with a Dark Matter Portal
The minimal extension of the MSSM (NMSSM) has been widely studied in the
search for a natural solution to the problem. In this work, we consider a
variation of the NMSSM where an extra singlet is added and a Peccei-Quinn
symmetry is imposed. We study its neutralino sector and compute the
annihilation cross section of the lightest neutralino. We use existent
cosmological and collider data to constrain the parameter space and consider
the lightest neutralino, which is very light, as a dark matter candidate.Comment: 26 pages, 8 figures . v4: minor corrections; version accepted for
publicatio
Dynamics of Relaxed Inflation
The cosmological relaxation of the electroweak scale has been proposed as a
mechanism to address the hierarchy problem of the Standard Model. A field, the
relaxion, rolls down its potential and, in doing so, scans the squared mass
parameter of the Higgs, relaxing it to a parametrically small value. In this
work, we promote the relaxion to an inflaton. We couple it to Abelian gauge
bosons, thereby introducing the necessary dissipation mechanism which slows
down the field in the last stages. We describe a novel reheating mechanism,
which relies on the gauge-boson production leading to strong electromagnetic
fields, and proceeds via the vacuum production of electron-positron pairs
through the Schwinger effect. We refer to this mechanism as Schwinger
reheating. We discuss the cosmological dynamics of the model and the
phenomenological constraints from CMB and other experiments. We find that a
cutoff close to the Planck scale may be achieved. In its minimal form, the
model does not generate sufficient curvature perturbations and additional
ingredients, such as a curvaton field, are needed.Comment: 39 pages, 3 figures, appendices D and E added, published in JHE
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