1,355 research outputs found
Yet Another Model of Soft Gamma Repeaters
We develop a model of SGR in which a supernova leaves planets orbiting a
neutron star in intersecting eccentric orbits. These planets will collide in
years if their orbits are coplanar. Some fragments of debris lose
their angular momentum in the collision and fall onto the neutron star,
producing a SGR. The initial accretion of matter left by the collision with
essentially no angular momentum may produce a superburst like that of March 5,
1979, while debris fragments which later lose their angular momentum produce an
irregular pattern of smaller bursts.Comment: 16pp, Tex, WU-JIK-94-
Inappropriateness of the Rindler quantization
It is argued that the Rindler quantization is not a correct approach to study
the effects of acceleration on quantum fields. First, the "particle"-detector
approach based on the Minkowski quantization is not equivalent to the approach
based on the Rindler quantization. Second, the event horizon, which plays the
essential role in the Rindler quantization, cannot play any physical role for a
local noninertial observer.Comment: 3 pages, accepted for publication in Mod. Phys. Lett.
Dynamics and symmetries of a field partitioned by an accelerated frame
The canonical evolution and symmetry generators are exhibited for a
Klein-Gordon (K-G) system which has been partitioned by an accelerated
coordinate frame into a pair of subsystems. This partitioning of the K-G system
is conveyed to the canonical generators by the eigenfunction property of the
Minkowski Bessel (M-B) modes. In terms of the M-B degrees of freedom, which are
unitarily related to those of the Minkowski plane waves, a near complete
diagonalization of these generators can be realized.Comment: 14 pages, PlainTex. Related papers on accelerated frames available at
http://www.math.ohio-state.edu/~gerlac
Interpolating between the Bose-Einstein and the Fermi-Dirac distributions in odd dimensions
We consider the response of a uniformly accelerated monopole detector that is
coupled to a superposition of an odd and an even power of a quantized, massless
scalar field in flat spacetime in arbitrary dimensions. We show that, when the
field is assumed to be in the Minkowski vacuum, the response of the detector is
characterized by a Bose-Einstein factor in even spacetime dimensions, whereas a
Bose-Einstein as well as a Fermi-Dirac factor appear in the detector response
when the dimension of spacetime is odd. Moreover, we find that, it is possible
to interpolate between the Bose-Einstein and the Fermi-Dirac distributions in
odd spacetime dimensions by suitably adjusting the relative strengths of the
detector's coupling to the odd and the even powers of the scalar field. We
point out that the response of the detector is always thermal and we, finally,
close by stressing the apparent nature of the appearance of the Fermi-Dirac
factor in the detector response.Comment: RevTeX, 7 page
Influence Functionals and the Accelerating Detector
The influence functional is derived for a massive scalar field in the ground
state, coupled to a uniformly accelerating DeWitt monopole detector in
dimensional Minkowski space. This confirms the local nature of the Unruh
effect, and provides an exact solution to the problem of the accelerating
detector without invoking a non-standard quantization. A directional detector
is presented which is efficiently decohered by the scalar field vacuum, and
which illustrates an important difference between the quantum mechanics of
inertial and non-inertial frames. From the results of these calculations, some
comments are made regarding the possibility of establishing a quantum
equivalence principle, so that the Hawking effect might be derived from the
Unruh effect.Comment: 32 page
Complete Insecurity of Quantum Protocols for Classical Two-Party Computation
A fundamental task in modern cryptography is the joint computation of a
function which has two inputs, one from Alice and one from Bob, such that
neither of the two can learn more about the other's input than what is implied
by the value of the function. In this Letter, we show that any quantum protocol
for the computation of a classical deterministic function that outputs the
result to both parties (two-sided computation) and that is secure against a
cheating Bob can be completely broken by a cheating Alice. Whereas it is known
that quantum protocols for this task cannot be completely secure, our result
implies that security for one party implies complete insecurity for the other.
Our findings stand in stark contrast to recent protocols for weak coin tossing,
and highlight the limits of cryptography within quantum mechanics. We remark
that our conclusions remain valid, even if security is only required to be
approximate and if the function that is computed for Bob is different from that
of Alice.Comment: v2: 6 pages, 1 figure, text identical to PRL-version (but reasonably
formatted
Radiation from a uniformly accelerating harmonic oscillator
We consider a radiation from a uniformly accelerating harmonic oscillator
whose minimal coupling to the scalar field changes suddenly. The exact time
evolutions of the quantum operators are given in terms of a classical solution
of a forced harmonic oscillator. After the jumping of the coupling constant
there occurs a fast absorption of energy into the oscillator, and then a slow
emission follows. Here the absorbed energy is independent of the acceleration
and proportional to the log of a high momentum cutoff of the field. The emitted
energy depends on the acceleration and also proportional to the log of the
cutoff. Especially, if the coupling is comparable to the natural frequency of
the detector () enormous energies are radiated away
from the oscillator.Comment: 26 pages, 1 eps figure, RevTeX, minor correction in grammar, add a
discussio
Quantum buoyancy, generalized second law, and higher-dimensional entropy bounds
Bekenstein has presented evidence for the existence of a universal upper
bound of magnitude to the entropy-to-energy ratio of an
arbitrary {\it three} dimensional system of proper radius and negligible
self-gravity. In this paper we derive a generalized upper bound on the
entropy-to-energy ratio of a -dimensional system. We consider a box full
of entropy lowered towards and then dropped into a -dimensional black
hole in equilibrium with thermal radiation. In the canonical case of three
spatial dimensions, it was previously established that due to quantum buoyancy
effects the box floats at some neutral point very close to the horizon. We find
here that the significance of quantum buoyancy increases dramatically with the
number of spatial dimensions. In particular, we find that the neutral
(floating) point of the box lies near the horizon only if its length is
large enough such that , where is the Compton length of the
body and for . A consequence is that quantum
buoyancy severely restricts our ability to deduce the universal entropy bound
from the generalized second law of thermodynamics in higher-dimensional
spacetimes with . Nevertheless, we find that the universal entropy bound
is always a sufficient condition for operation of the generalized second law in
this type of gedanken experiments.Comment: 6 page
Measurement of Time-of-Arrival in Quantum Mechanics
It is argued that the time-of-arrival cannot be precisely defined and
measured in quantum mechanics. By constructing explicit toy models of a
measurement, we show that for a free particle it cannot be measured more
accurately then , where is the initial kinetic
energy of the particle. With a better accuracy, particles reflect off the
measuring device, and the resulting probability distribution becomes distorted.
It is shown that a time-of-arrival operator cannot exist, and that approximate
time-of-arrival operators do not correspond to the measurements considered
here.Comment: References added. To appear in Phys. Rev.
Fluctuation-dissipation theorem and the Unruh effect of scalar and Dirac fields
We present a simple and systematic method to calculate the Rindler noise,
which is relevant to the analysis of the Unruh effect, by using the
fluctuation-dissipative theorem. To do this, we calculate the dissipative
coefficient explicitly from the equations of motion of the detector and the
field. This method gives not only the correct answer but also a hint as to the
origin of the apparent statistics inversion effect. Moreover, this method is
generalized to the Dirac field, by using the fermionic fluctuation-dissipation
theorem. We can thus confirm that the fermionic fluctuation-dissipation theorem
is working properly.Comment: 26 page
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