1,101 research outputs found
Treaty Exit in the United States: Insights from the United Kingdom or South Africa?
This essay, a contribution to an AJIL Unbound symposium on âTreaty Exit at the Interface of Domestic and International Law,â compares treaty exit in the United States, the United Kingdom, and South Africa. After examining the longstanding practice of unilateral presidential withdrawals from treaties in the United States and the refusal to date of U.S. courts to review the constitutionality of that practice, the essay summarizes recent judicial decisions in the United Kingdom and South Africa holding that parliamentary approval was required before these nations could withdraw from treaties committing them, respectively, to the European Union and the International Criminal Court. We conclude that these decisionsâwhile important and interesting in their own rightâoffer limited insights for debates in the United States over whether the President has unilateral treaty withdrawal authority and how such withdrawals might affect statutes implementing international agreements
Moving Mirrors and Thermodynamic Paradoxes
Quantum fields responding to "moving mirrors" have been predicted to give
rise to thermodynamic paradoxes. I show that the assumption in such work that
the mirror can be treated as an external field is invalid: the exotic
energy-transfer effects necessary to the paradoxes are well below the scales at
which the model is credible. For a first-quantized point-particle mirror, it
appears that exotic energy-transfers are lost in the quantum uncertainty in the
mirror's state. An accurate accounting of these energies will require a model
which recognizes the mirror's finite reflectivity, and almost certainly a model
which allows for the excitation of internal mirror modes, that is, a
second-quantized model.Comment: 7 pages, Revtex with Latex2
Gravitational Wave Emission from Collisions of Compact Scalar Solitons
We numerically investigate the gravitational waves generated by the head-on
collision of equal-mass, self-gravitating, real scalar field solitons
(oscillatons) as a function of their compactness . We show that
there exist three different possible outcomes for such collisions: (1) an
excited stable oscillaton for low , (2) a merger and formation of
a black-hole for intermediate , and (3) a pre-merger collapse of
both oscillatons into individual black-holes for large . For (1),
the excited, aspherical oscillaton continues to emit gravitational waves. For
(2), the total energy in gravitational waves emitted increases with
compactness, and possesses a maximum which is greater than that from the merger
of a pair of equivalent mass black-holes. The initial amplitudes of the
quasi-normal modes in the post-merger ring-down in this case are larger than
that of corresponding mass black-holes -- potentially a key observable to
distinguish black-hole mergers with their scalar mimics. For (3), the
gravitational wave output is indistinguishable from a similar mass,
black-hole--black-hole merger.Comment: 8 Pages, 8 figures, movies :
https://www.youtube.com/playlist?list=PLSkfizpQDrcahgvc5TvBk5qtXAzkSyHP
Formation of Relativistic Axion Stars
Axions and axion-like particles are compelling candidates for the missing
dark matter of the universe. As they undergo gravitational collapse, they can
form compact objects such as axion stars or even black holes. In this paper, we
study the formation and distribution of such objects. First, we simulate the
formation of compact axion stars using numerical relativity with aspherical
initial conditions that could represent the final stages of axion dark matter
structure formation. We show that the final states of such collapse closely
follow the known relationship of initial mass and axion decay constant .
Second, we demonstrate with a toy model how this information can be used to
scan a model density field to predict the number densities and masses of such
compact objects. In addition to being detectable by the LIGO/VIRGO
gravitational wave interferometer network for axion mass of eV, we show using peak statistics that for , there
exists a "mass gap" between the masses of axion stars and black holes formed
from collapse
The electromagnetic field near a dielectric half-space
We compute the expectations of the squares of the electric and magnetic
fields in the vacuum region outside a half-space filled with a uniform
non-dispersive dielectric. This gives predictions for the Casimir-Polder force
on an atom in the `retarded' regime near a dielectric. We also find a positive
energy density due to the electromagnetic field. This would lead, in the case
of two parallel dielectric half-spaces, to a positive, separation-independent
contribution to the energy density, besides the negative, separation-dependent
Casimir energy. Rough estimates suggest that for a very wide range of cases,
perhaps including all realizable ones, the total energy density between the
half-spaces is positive.Comment: Latex2e, IOP macros, 15 pages, 2 eps figure
General Relativistic Polarized Proca Stars
Massive vector fields can form spatially localized, non-relativistic,
stationary field configurations supported by gravitational interactions. The
ground state configurations (p-solitons/vector solitons/dark photon
stars/polarized Proca stars) have a time-dependent vector field pointing in the
same spatial direction throughout the configuration at any instant of time, can
carry macroscopic amounts of spin angular momentum, and are spherically
symmetric and monotonic in the energy density. In this paper, we include
general relativistic effects, and numerically investigate the stability of
compact polarized Proca stars (linear and circularly polarized) and compare
them to hedgehog-like field configurations (with radially pointing field
directions). Starting with approximate field profiles of such stars, we evolve
the system numerically using 3+1 dimensional numerical simulations in general
relativity. We find that these initial conditions lead to stable
configurations. However, at sufficiently large initial compactness, they can
collapse to black holes. We find that the initial compactness that leads to
black hole formation is higher for circularly polarized stars (which carry
macroscopic spin angular momentum), compared to linearly polarized ones, which
in turn is higher than that for hedgehog configurations.Comment: 10 pages, 6 figure
Non-Gaussian curvature distribution of actin-propelled biomimetric colloid trajectories
We analyze the motion of colloids propelled by a comet-like tail of polymerizing actin filaments. The curvature of the particle trajectories deviates strongly from a Gaussian distribution, implying that the underlying microscopic processes are fluctuating in a non-independent manner. Trajectories for beads of different size all showed the same non-Gaussian behavior, while the mean curvature decreased weakly with size. A stochastic simulation that includes nucleation, force-dependent dissociation, growth, and capping of filaments, shows that the non-Gaussian curvature distribution can be explained by a positive feedback mechanism in which attached chains under higher tension are more likely to sna
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