32 research outputs found
Time Evolution of Temperature and Entropy of Various Collapsing Domain Walls
We investigate the time evolution of the temperature and entropy of
gravitationally collapsing domain walls as seen by an asymptotic observer. In
particular, we seek to understand how topology and the addition of a
cosmological constant affect the gravitational collapse. Previous work has
shown that the entropy of a spherically symmetric collapsing domain approaches
a constant. In this paper, we reproduce these results, using both a fully
quantum and a semi-classical approach, then we repeat the process for a de
Sitter Schwarzschild domain wall (spherical with cosmological constant) and a
(3+1) BTZ domain wall (cylindrical). We do this by coupling a scalar field to
the background of the domain wall and analyzing the spectrum of radiation as a
function of time. We find that the spectrum is quasi-thermal, with the degree
of thermality increasing as the domain wall approaches the horizon. The thermal
distribution allows for the determination of the temperature as a function of
time, and we find that the late time temperature is very close to the Hawking
temperature and that it also exhibits the proper scaling with the mass. From
the temperature we find the entropy. Since the collapsing domain wall is what
forms a black hole, we can compare the results to those of the standard
entropy-area relation. We find that the entropy does in fact approach a
constant that is close to the Hawking entropy. However, both the de Sitter
Schwarzschild domain wall and the (3+1) BTZ domain wall show periods of
decreasing entropy, which suggests that spontaneous collapse may be prevented.Comment: This paper is a merging of two previously submitted papers: Time
Evolution of Temperature and Entropy of a Gravitationally Collapsing Cylinder
[arXiv:1106.2278]; Time Evolution of Temperature and Entropy of a
Gravitationally Collapsing de Sitter Schwarzschild Domain Wal
Dark energy, the electroweak vacua and collider phenomenology
Higher dimensional non-renormalizable operators may modify the Standard Model
Higgs potential in many interesting ways. Here, we consider the appearance of a
second vacuum which may play an important role in cosmology. For the certain
range of parameters, the usual second order electroweak phase transition is
followed by a first order phase transition that may drive the late time
accelerated expansion of the universe. Such a potential contains kink-like
solutions which in turn can play a crucial role in reconstructing the global
shape of the potential in colliders, as we explicitly demonstrate.Comment: Expanded version. Published in Phys. Rev.
Classical and Quantum Equations of Motion for a BTZ Black String in AdS Space
We investigate gravitational collapse of a -dimensional BTZ black
string in AdS space in the context of both classical and quantum mechanics.
This is done by first deriving the conserved mass per unit length of the
cylindrically symmetric domain wall, which is taken as the classical
Hamiltonian of the black string. In the quantum mechanical context, we take
primary interest in the behavior of the collapse near the horizon and near the
origin (classical singularity) from the point of view of an infalling observer.
In the absence of radiation, quantum effects near the horizon do not change the
classical conclusions for an infalling observer, meaning that the horizon is
not an obstacle for him/her. The most interesting quantum mechanical effect
comes in when investigating near the origin. First, quantum effects are able to
remove the classical singularity at the origin, since the wave function is
non-singular at the origin. Second, the Schr\"odinger equation describing the
behavior near the origin displays non-local effects, which depend on the energy
density of the domain wall. This is manifest in that derivatives of the
wavefunction at one point are related to the value of the wavefunction at some
other distant point.Comment: 9 pages, 1 figure. Minor Clarification and corrections. Accepted for
Publication in JHE
Priority research needs to inform amphibian conservation in the Anthropocene
The problem of global amphibian declines has prompted extensive research over the last three decades. Initially, the focus was on identifying and characterizing the extent of the problem, but more recently efforts have shifted to evidenceâbased research designed to identify best solutions and to improve conservation outcomes. Despite extensive accumulation of knowledge on amphibian declines, there remain knowledge gaps and disconnects between science and action that hamper our ability to advance conservation efforts. Using input from participants at the ninth World Congress of Herpetology, a U.S. Geological Survey Powell Center symposium, amphibian onâline forums for discussion, the International Union for Conservation of Nature Assisted Reproductive Technologies and Gamete Biobanking group, and respondents to a survey, we developed a list of 25 priority research questions for amphibian conservation at this stage of the Anthropocene. We identified amphibian conservation research priorities while accounting for expected tradeoffs in geographic scope, costs, and the taxonomic breadth of research needs. We aimed to solicit views from individuals rather than organizations while acknowledging inequities in participation. Emerging research priorities (i.e., those underârepresented in recently published amphibian conservation literature) were identified, and included the effects of climate change, communityâlevel (rather than single speciesâlevel) drivers of declines, methodological improvements for research and monitoring, genomics, and effects of landâuse change. Improved inclusion of underârepresented members of the amphibian conservation community was also identified as a priority. These research needs represent critical knowledge gaps for amphibian conservation although filling these gaps may not be necessary for many conservation actions