1,870 research outputs found
Affleck-Dine baryogenesis just after inflation
We propose a new scenario of Affleck-Dine baryogenesis where a flat direction
in the MSSM generates B-L asymmetry just after the end of inflation. The
resulting amount of baryon asymmetry is independent of low-energy
supersymmetric models but is dependent on inflation models. We consider the
hybrid and chaotic inflation models and find that reheating temperature is
required to be higher than that in the conventional scenario of Affleck-Dine
baryogenesis. In particular, non-thermal gravitino-overproduction problem is
naturally avoided in the hybrid inflation model. Our results imply that
Affleck-Dine baryogenesis can be realized in a broader range of supersymmetry
and inflation models than expected in the literature.Comment: 35 pages, 7 figure
Anthropic Bound on Dark Radiation and its Implications for Reheating
We derive an anthropic bound on the extra neutrino species, , based on the observation that a positive suppresses
the growth of matter fluctuations due to the prolonged radiation dominated era,
which reduces the fraction of matter that collapses into galaxies, hence, the
number of observers. We vary and the positive cosmological
constant while fixing the other cosmological parameters. We then show that the
probability of finding ourselves in a universe satisfying the current bound is
of order a few percents for a flat prior distribution. If
is found to be close to the current upper bound or the value suggested by the
tension, the anthropic explanation is not very unlikely. On the other
hand, if the upper bound on is significantly improved by
future observations, such simple anthropic consideration does not explain the
small value of . We also study simple models where dark
radiation consists of relativistic particles produced by heavy scalar decays,
and show that the prior probability distribution sensitively depends on the
number of the particle species.Comment: 14 pages, 4 figures; V2: Added references; V3: Published version,
Added the anthropic bound on the number of neutrino flavor
Hessian eigenvalue distribution in a random Gaussian landscape
The energy landscape of multiverse cosmology is often modeled by a
multi-dimensional random Gaussian potential. The physical predictions of such
models crucially depend on the eigenvalue distribution of the Hessian matrix at
potential minima. In particular, the stability of vacua and the dynamics of
slow-roll inflation are sensitive to the magnitude of the smallest eigenvalues.
The Hessian eigenvalue distribution has been studied earlier, using the saddle
point approximation, in the leading order of expansion, where is the
dimensionality of the landscape. This approximation, however, is insufficient
for the small eigenvalue end of the spectrum, where sub-leading terms play a
significant role. We extend the saddle point method to account for the
sub-leading contributions. We also develop a new approach, where the eigenvalue
distribution is found as an equilibrium distribution at the endpoint of a
stochastic process (Dyson Brownian motion). The results of the two approaches
are consistent in cases where both methods are applicable. We discuss the
implications of our results for vacuum stability and slow-roll inflation in the
landscape.Comment: 33 pages, 10 figure
Primordial Black Holes from Polynomial Potentials in Single Field Inflation
Within canonical single field inflation models, we provide a method to
reverse engineer and reconstruct the inflaton potential from a given power
spectrum. This is not only a useful tool to find a potential from observational
constraints, but also gives insight into how to generate a large amplitude
spike in density perturbations, especially those that may lead to primordial
black holes (PBHs). In accord with other works, we find that the usual
slow-roll conditions need to be violated in order to generate a significant
spike in the spectrum. We find that a way to achieve a very large amplitude
spike in single field models is for the classical roll of the inflaton to
over-shoot a local minimum during inflation. We provide an example of a quintic
polynomial potential that implements this idea and leads to the observed
spectral index, observed amplitude of fluctuations on large scales, significant
PBH formation on small scales, and is compatible with other observational
constraints. We quantify how much fine-tuning is required to achieve this in a
family of random polynomial potentials, which may be useful to estimate the
probability of PBH formation in the string landscape.Comment: 13 pages in double column format, 5 figures. V2: Added references and
small clarification
Vacuum Decay in Real Time and Imaginary Time Formalisms
We analyze vacuum tunneling in quantum field theory in a general formalism by
using the Wigner representation. In the standard instanton formalism, one
usually approximates the initial false vacuum state by an eigenstate of the
field operator, imposes Dirichlet boundary conditions on the initial field
value, and evolves in imaginary time. This approach does not have an obvious
physical interpretation. However, an alternative approach does have a physical
interpretation: in quantum field theory, tunneling can happen via classical
dynamics, seeded by initial quantum fluctuations in both the field and its
momentum conjugate, which was recently implemented in Ref. [1]. We show that
the Wigner representation is a useful framework to calculate and understand the
relationship between these two approaches. We find there are two, related,
saddle point approximations for the path integral of the tunneling process: one
corresponds to the instanton solution in imaginary time and the other one
corresponds to classical dynamics from initial quantum fluctuations in real
time. The classical approximation for the dynamics of the latter process is
justified only in a system with many degrees of freedom, as can appear in field
theory due to high occupancy of nucleated bubbles, while it is not justified in
single particle quantum mechanics, as we explain. We mention possible
applications of the real time formalism, including tunneling when the instanton
vanishes, or when the imaginary time contour deformation is not possible, which
may occur in cosmological settings.Comment: 10 pages in double column format, 2 figures. V2: Further
clarifications. Updated to resemble version published in PR
- β¦