73 research outputs found
Electroweak Baryogenesis and the Standard Model Effective Field Theory
We investigate electroweak baryogenesis within the framework of the Standard
Model Effective Field Theory. The Standard Model Lagrangian is supplemented by
dimension-six operators that facilitate a strong first-order electroweak phase
transition and provide sufficient CP violation. Two explicit scenarios are
studied that are related via the classical equations of motion and are
therefore identical at leading order in the effective field theory expansion.
We demonstrate that formally higher-order dimension-eight corrections lead to
large modifications of the matter-antimatter asymmetry. The effective field
theory expansion breaks down in the modified Higgs sector due to the
requirement of a first-order phase transition. We investigate the source of the
breakdown in detail and show how it is transferred to the CP-violating sector.
We briefly discuss possible modifications of the effective field theory
framework.Comment: 21 pages + appendices. V2: Corrected a factor-2 mistake which has
changed the results for the baryon asymmetry quantitatively. Main conclusions
of the v1 still hol
Renormalization Group Equations of Higgs- Inflation
We derive one- and two-loop renormalization group equations (RGEs) of
Higgs- inflation. This model has a non-minimal coupling between the Higgs
and the Ricci scalar and a Ricci scalar squared term on top of the standard
model. The RGEs derived in this paper are valid as long as the energy scale of
interest (in the Einstein frame) is below the Planck scale. We also discuss
implications to the inflationary predictions and the electroweak vacuum
metastability.Comment: 35 pages, 1 figure; v2: references added, version accepted by JHE
Model-independent energy budget of cosmological first-order phase transitions
We study the energy budget of a first-order cosmological phase transition,
which is an important factor in the prediction of the resulting gravitational
wave spectrum. Formerly, this analysis was based mostly on simplified models as
for example the bag equation of state. Here, we present a model-independent
approach that is exact up to the temperature dependence of the speed of sound
in the broken phase. We find that the only relevant quantities that enter in
the hydrodynamic analysis are the speed of sound in the broken phase and a
linear combination of the energy and pressure differences between the two
phases which we call pseudotrace (normalized to the enthalpy in the broken
phase). The pseudotrace quantifies the strength of the phase transition and
yields the conventional trace of the energy-momentum tensor for a relativistic
plasma (with speed of sound squared of one third). We study this approach in
several realistic models of the phase transition and also provide a code
snippet that can be used to determine the efficiency coefficient for a given
phase transition strength and speed of sound. It turns out that our approach is
accurate to the percent level for moderately strong phase transitions, while
former approaches give at best the right order of magnitude.Comment: 24 pages, 2 figure
Resummation and cancellation of the VIA source in electroweak baryogenesis
We re-derive the vev-insertion approximation (VIA) source in electroweak
baryogenesis. In contrast to the original derivation, we rely solely on
1-particle-irreducible self-energy diagrams. We solve the Green's function
equations both perturbatively and resummed over all vev-insertions. The VIA
source corresponds to the leading order contribution in the gradient expansion
of the Kadanoff-Baym (KB) equations. We find that it vanishes both for bosons
and fermions, both in the perturbative and in the resummed approach.
Interestingly, the non-existence of the source is a result of a cancellation
between different terms in the KB equations, and not of a pathology in the
vev-insertion approximation itself.Comment: 29 Page
Model-independent bubble wall velocities in local thermal equilibrium
Accurately determining bubble wall velocities in first-order phase
transitions is of great importance for the prediction of gravitational wave
signals and the matter-antimatter asymmetry. However, it is a challenging task
which typically depends on the underlying particle physics model. Recently, it
has been shown that assuming local thermal equilibrium can provide a good
approximation when calculating the bubble wall velocity. In this paper, we
provide a model-independent determination of bubble wall velocities in local
thermal equilibrium. Our results show that, under the reasonable assumption
that the sound speeds in the plasma are approximately uniform, the
hydrodynamics can be fully characterized by four quantities: the phase strength
, the ratio of the enthalpies in the broken and symmetric phases,
, and the sound speeds in both phases, and . We provide a
code snippet that allows for a determination of the wall velocity and energy
fraction in local thermal equilibrium in any model. In addition, we present a
fit function for the wall velocity in the case .Comment: 34 pages, 6 figures; v2 matches published versio
Ultrametricity increases the predictability of cultural dynamics
A quantitative understanding of societies requires useful combinations of empirical data and mathematical models. Models of cultural dynamics aim at explaining the emergence of culturally homogeneous groups through social influence. Traditionally, the initial cultural traits of individuals are chosen uniformly at random, the emphasis being on characterizing the model outcomes that are independent of these (`annealed') initial conditions. Here, motivated by an increasing interest in forecasting social behavior in the real world, we reverse the point of view and focus on the effect of specific (`quenched') initial conditions, including those obtained from real data, on the final cultural state. We study the predictability, rigorously defined in an information-theoretic sense, of the \emphsocial content of the final cultural groups (i.e. who ends up in which group) from the knowledge of the initial cultural traits. We find that, as compared to random and shuffled initial conditions, the hierarchical ultrametric-like organization of empirical cultural states significantly increases the predictability of the final social content by largely confining cultural convergence within the lower levels of the hierarchy. Moreover, predictability correlates with the compatibility of short-term social coordination and long-term cultural diversity, a property that has been recently found to be strong and robust in empirical data. We also introduce a null model generating initial conditions that retain the ultrametric representation of real data. Using this ultrametric model, predictability is highly enhanced with respect to the random and shuffled cases, confirming the usefulness of the empirical hierarchical organization of culture for forecasting the outcome of social influence models
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