11,855 research outputs found

### Towards observable signatures of other bubble universes II: Exact solutions for thin-wall bubble collisions

We assess the effects of a collision between two vacuum bubbles in the
thin-wall limit. After describing the outcome of a generic collision possessing
the expected hyperbolic symmetry, we focus on collisions experienced by a
bubble containing positive vacuum energy, which could in principle contain our
observable universe. We provide criteria governing whether the post-collision
domain wall accelerates towards or away from this "observation" bubble, and
discuss the implications for observers located at various positions inside of
the bubble. Then, we identify the class of solutions which have minimal impact
on the interior of the observation bubble, and derive a simple formula for the
energy density of a shell of radiation emitted from such a collision. In the
context of a universe undergoing false vacuum eternal inflation, these
solutions are perhaps the most promising candidates for collisions that could
exist within our past light cone, and therefore in principle be observable.Comment: 18 PRD-style pages, 12 figures. Added appendix on the expected number
of collisions, added references, minor correction to Appendix C, conclusions
unchanged. Replaced to match published versio

### Hurdles for Recent Measures in Eternal Inflation

In recent literature on eternal inflation, a number of measures have been
introduced which attempt to assign probabilities to different pocket universes
by counting the number of each type of pocket according to a specific
procedure. We give an overview of the existing measures, pointing out some
interesting connections and generic predictions. For example, pairs of vacua
that undergo fast transitions between themselves will be strongly favored. The
resultant implications for making predictions in a generic potential landscape
are discussed. We also raise a number of issues concerning the types of
transitions that observers in eternal inflation are able to experience.Comment: 15 PRD-style pages, 5 figures, expanded discussion of measures in
Sec. II, added reference

### Eternal Inflation With Non-Inflationary Pocket Universes

Eternal inflation produces pocket universes with all physically allowed vacua
and histories. Some of these pocket universes might contain a phase of
slow-roll inflation, some might undergo cycles of cosmological evolution and
some might look like the galilean genesis or other "emergent" universe
scenarios. Which one of these types of universe we are most likely to inhabit
depends on the measure we choose in order to regulate the infinities inherent
in eternal inflation. We show that the currently leading measure proposals,
namely the global light-cone cut-off and its local counterpart, the causal
diamond measure, as well as closely related proposals, all predict that we
should live in a pocket universe that starts out with a small Hubble rate, thus
favoring emergent and cyclic models. Pocket universes which undergo cycles are
further preferred, because they produce habitable conditions repeatedly inside
each pocket.Comment: 13 pages, 2 figures, v2: replaced with PRD versio

### Suspension flow: do particles act as mixers?

Recently, Roht et al. [J. Contam. Hydrol. 145, 10-16 (2013)] observed that
the presence of suspended non-Brownian macroscopic particles decreased the
dispersivity of a passive solute, for a pressure-driven flow in a narrow
parallel-plates channel at low Reynolds number. This result contradicts the
idea that the streamline distortion caused by the random diffusive motion of
the particles increases the dispersion and mixing of the solute. Therefore, to
estimate the influence of this motion on the dispersivity of the solute, and
investigate the origin of the reported decrease, we experimentally studied the
probability density functions (pdf) of the particle velocities, and
spatio-temporal correlations, in the same experimental configuration. We
observed that, as the mean suspension velocity exceeds a critical value, the
pdf of the streamwise velocities of the particles markedly changes from a
symmetric distribution to an asymmetric one strongly skewed to high velocities
and with a peak of most probable velocity close to the maximum velocity. The
latter observations and the analysis of suspension microstructure indicate that
the observed decrease in the dispersivity of the solute is due to particle
migration to the mid-plane of the channel, and consequent flattening of the
velocity profile. Moreover, we estimated the contribution of particle diffusive
motion to the solute dispersivity to be three orders of magnitude smaller than
the reported decrease, and thus negligible. Solute dispersion is then much more
affected by how particles modify the flow velocity profile across the channel,
than by their diffusive random motion

### Propagation of mesons in asymmetric nuclear matter in a density dependent coupling model

We study the propagation of the light mesons sigma, omega, rho, and a0(980)
in dense hadronic matter in an extended derivative scalar coupling model.
Within the scheme proposed it is possible to unambiguously define effective
density-dependent couplings at the Lagrangian level. We first apply the model
to study asymmetric nuclear matter with fixed isospin asymmetry, and then we
pay particular attention to hypermatter in beta-equilibrium. The equation of
state and the potential contribution to the symmetry coefficient arising from
the mean field approximation are investigated.Comment: 17 pages, 15 PostScript figure

### A supersymmetric exotic field theory in (1+1) dimensions. One loop soliton quantum mass corrections

We consider one loop quantum corrections to soliton mass for the ${\cal N}=1$
supersymmetric extension of the (1+1)-dimensional scalar field theory with the
potential $U(\phi) = \phi^2 \cos^2\left(\ln \phi^2\right)$. First, we compute
the one loop quantum soliton mass correction of the bosonic sector. To do that,
we regularize implicitly such quantity by subtracting and adding its
corresponding tadpole graph contribution, and use the renormalization
prescription that the added term vanishes with the corresponding counterterms.
As a result we get a finite unambiguous formula for the soliton quantum mass
corrections up to one loop order. Afterwards, the computation for the
supersymmetric case is extended straightforwardly and we obtain for the one
loop quantum correction of the SUSY kink mass the expected value previously
derived for the SUSY sine-Gordon and $\phi^4$ models. However, we also have
found that for a particular value of the parameters, contrary to what was
expected, the introduction of supersymmetry in this model worsens ultraviolet
divergences rather than improving them.Comment: 16 pages, 8 figures; Major modifications included to match version
published in JHE

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