5,045 research outputs found
Attractor Explosions and Catalyzed Vacuum Decay
We present a mechanism for catalyzed vacuum bubble production obtained by
combining moduli stabilization with a generalized attractor phenomenon in which
moduli are sourced by compact objects. This leads straightforwardly to a class
of examples in which the Hawking decay process for black holes unveils a bubble
of a different vacuum from the ambient one, generalizing the new endpoint for
Hawking evaporation discovered recently by Horowitz. Catalyzed vacuum bubble
production can occur for both charged and uncharged bodies, including
Schwarzschild black holes for which massive particles produced in the Hawking
process can trigger vacuum decay. We briefly discuss applications of this
process to the population and stability of metastable vacua.Comment: 26 pages harvmac big; 2 figure
Difficulties with Recollapsing models in Closed Isotropic Loop Quantum Cosmology
The use of techniques from loop quantum gravity for cosmological models may
solve some difficult problems in quantum cosmology. The solutions under a
number of circumstances have been well studied. We will analyse the behaviour
of solutions in the closed model, focusing on the behaviour of a universe
containing a massless scalar field. The asymptotic behaviour of the solutions
is examined, and is used to determine requirements of the initial conditions.Comment: 10 pages, accepted to Phys. Rev.
The moss Bryum argenteum var. muticum Brid. is well adapted to cope with high light in continental Antarctica
The net photosynthetic rate (NP), chlorophyll fluorescence, carotenoid content and chlorophyll content of the cosmopolitan moss Bryum argenteum were measured in the field at Botany Bay, southern Victoria Land, continental Antarctica (77°S). Comparisons were made between sun- and shade-adapted forms, and changes were followed as the moss emerged from under the snow and during exposure of shade and sun forms to ambient light. Shade forms had lower light compensation and saturation values for NP but little difference in maximal NP rates. Shade forms exposed to ambient light changed rapidly (within five days) towards the performance of the sun forms. Surprisingly, this change was not by acclimation of shoots but by the production of new shoots. Chlorophyll and carotenoid levels measured on a molar chlorophyll basis showed no difference between sun and shade forms and also little change during emergence. The constant molar relationship between carotenoids and chlorophyll plus the high levels of the xanthophyll cycle pigments suggest that protection of the chlorophyll antenna was constitutive. This is an adaptation to the very high light levels that occur when the plants are active in continental Antarctica and contrasts to the situation in more temperate areas where high light is normally avoided by desiccation
Rape and Posttraumatic Stress Disorder (PTSD): Examining the Mediating Role of Explicit Sex-Power Beliefs for Men Versus Women
Many rape survivors exhibit symptoms of post-traumatic stress disorder (PTSD), and recent literature suggests survivors\u27 beliefs about sex and control may affect PTSD symptoms. The present study examined beliefs about sex and power as potential mediators of the relationship between rape and PTSD symptoms for men versus women. Participants (N = 782) reported lifetime history of rape, current PTSD symptoms, and beliefs about sex and power. Women reported higher levels of lifetime history of rape than men (19.7% for women; 9.7% for men). While rape history predicted PTSD symptoms for both genders, beliefs about sex and power were shown to be a significant partial mediator of this relationship for men, but not for women. Results extend the literature on rape and PTSD by suggesting that survivors\u27 beliefs about sex and power are connected and can affect their PTSD symptoms. Additionally, results illustrate how sexual violence against men may reaffirm male gender roles that entail power and aggression, and ultimately affect trauma recovery
A Comment on Zero-brane Quantum Mechanics
We consider low energy, non-relativistic scattering of two Dirichlet
zero-branes as an exercise in quantum mechanics. For weak string coupling and
sufficiently small velocity, the dynamics is governed by an effective U(2)
gauge theory in 0+1 dimensions. At low energies, D-brane scattering can
reliably probe distances much shorter than the string scale. The only length
scale in the quantum mechanics problem is the eleven dimensional Planck length.
This provides evidence for the role of scales shorter than the string length in
the weakly coupled dynamics of type IIA strings.Comment: 9 pages, harvmac, improved treatment of 2+1 proble
Curvature Perturbations From Stochastic Particle Production During Inflation
We calculate the curvature power spectrum sourced by spectator fields that
are excited repeatedly and non-adiabatically during inflation. In the absence
of detailed information of the nature of spectator field interactions, we
consider an ensemble of models with intervals between the repeated interactions
and interaction strengths drawn from simple probabilistic distributions. We
show that the curvature power spectra of each member of the ensemble shows rich
structure with many features, and there is a large variability between
different realizations of the same ensemble. Such features can be probed by the
cosmic microwave background (CMB) and large scale structure observations. They
can also have implications for primordial black hole formation and CMB spectral
distortions.
The geometric random walk behavior of the spectator field allows us to
calculate the ensemble-averaged power spectrum of curvature perturbations
semi-analytically. For sufficiently large stochastic sourcing, the
ensemble-averaged power spectrum shows a scale dependence arising from the time
spent by modes outside the horizon during the period of particle production, in
spite of there being no preferred scale in the underlying model. We find that
the magnitude of the ensemble-averaged power spectrum overestimates the typical
power spectra in the ensemble because the ensemble distribution of the power
spectra is highly non-Gaussian with fat tails.Comment: 68 pages, 23 figure
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