751 research outputs found
OpenCell - Status and plans
Update on the current status of OpenCell ("www.opencell.org":http://www.opencell.org) and discussion of our plans for a new version of OpenCell
Renormalization out of equilibrium in a superrenormalizable theory
We discuss the renormalization of the initial value problem in Nonequilibrium
Quantum Field Theory within a simple, yet instructive, example and show how to
obtain a renormalized time evolution for the two-point functions of a scalar
field and its conjugate momentum at all times. The scheme we propose is
applicable to systems that are initially far from equilibrium and compatible
with non-secular approximation schemes which capture thermalization. It is
based on Kadanoff-Baym equations for non-Gaussian initial states, complemented
by usual vacuum counterterms. We explicitly demonstrate how various
cutoff-dependent effects peculiar to nonequilibrium systems, including
time-dependent divergences or initial-time singularities, are avoided by taking
an initial non-Gaussian three-point vacuum correlation into account.Comment: 5 pages, 2 figure
Interplay of super-WIMP and freeze-in production of dark matter
Non-thermalized dark matter is a cosmologically valid alternative to the
paradigm of weakly interacting massive particles. For dark matter belonging to
a -odd sector that contains in addition a thermalized mediator particle,
dark matter production proceeds in general via both the freeze-in and superWIMP
mechanism. We highlight their interplay and emphasize the connection to
long-lived particles at colliders. For the explicit example of a colored
t-channel mediator model we map out the entire accessible parameter space,
cornered by bounds from the LHC, big bang nucleosynthesis and Lyman-alpha
forest observations, respectively. We discuss prospects for the HL- and HE-LHC.Comment: 9 pages + references, 2 figures; v2: title changed, matches journal
versio
Medium corrections to the CP-violating parameter in leptogenesis
In two recent papers, arXiv:0909.1559 and arXiv:0911.4122, it has been
demonstrated that one can obtain quantum corrected Boltzmann kinetic equations
for leptogenesis using a top-down approach based on the
Schwinger-Keldysh/Kadanoff-Baym formalism. These "Boltzmann-like" equations are
similar to the ones obtained in the conventional bottom-up approach but differ
in important details. In particular there is a discrepancy between the
CP-violating parameter obtained in the first-principle derivation and in the
framework of thermal field theory. Here we demonstrate that the two approaches
can be reconciled if causal n-point functions are used in the thermal field
theory approach. The new result for the medium correction to the CP-violating
parameter is qualitatively different from the conventional one. The analogy to
a toy model considered earlier enables us to write down consistent quantum
corrected Boltzmann equations for thermal leptogenesis in the Standard Model
(supplemented by three right-handed neutrinos) which include quantum
statistical terms and medium corrected expressions for the CP-violating
parameter.Comment: 13 pages, 9 figure
Cosmological perturbation theory at three-loop order
We analyze the dark matter power spectrum at three-loop order in standard
perturbation theory of large scale structure. We observe that at late times the
loop expansion does not converge even for large scales (small momenta) well
within the linear regime, but exhibits properties compatible with an asymptotic
series. We propose a technique to restore the convergence in the limit of small
momentum, and use it to obtain a perturbative expansion with improved
convergence for momenta in the range where baryonic acoustic oscillations are
present. Our results are compared with data from N-body simulations at
different redshifts, and we find good agreement within this range.Comment: 29 pages, 8 figures, 1 table; v2 Typos corrected, references added.
Matches published versio
Signatures of Majorana dark matter with t-channel mediators
Three main strategies are being pursued to search for non-gravitational dark
matter signals: direct detection, indirect detection and collider searches.
Interestingly, experiments have reached sensitivities in these three search
strategies which may allow detection in the near future. In order to take full
benefit of the wealth of experimental data, and in order to confirm a possible
dark matter signal, it is necessary to specify the nature of the dark matter
particle and of the mediator to the Standard Model. In this paper, we focus on
a simplified model where the dark matter particle is a Majorana fermion that
couples to a light Standard Model fermion via a Yukawa coupling with a scalar
mediator. We review the observational signatures of this model and we discuss
the complementarity among the various search strategies, with emphasis in the
well motivated scenario where the dark matter particles are produced in the
early Universe via thermal freeze-out.Comment: 40+11 pages, 19 figures, review article, v2: matches published
versio
Leptogenesis: The Other Cuts
For standard leptogenesis from the decay of singlet right-handed neutrinos,
we derive source terms for the lepton asymmetry that are present in a finite
density background but absent in the vacuum. These arise from cuts through the
vertex correction to the decay asymmetry, where in the loop either the Higgs
boson and the right-handed neutrino or the left-handed lepton and the
right-handed neutrino are simultaneously on shell. We evaluate the source terms
numerically and use them to calculate the lepton asymmetry for illustrative
points in parameter space, where we consider only two right-handed neutrinos
for simplicity. Compared to calculations where only the standard cut through
the propagators of left-handed lepton and Higgs boson is included, sizable
corrections arise when the masses of the right-handed neutrinos are of the same
order, but the new sources are found to be most relevant when the decaying
right-handed neutrino is heavier than the one in the loop. In that situation,
they can yield the dominant contribution to the lepton asymmetry.Comment: 22 pages, 4 figure
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