791 research outputs found
Black-Hole Uncertainty Entails an Intrinsic Time Arrow. a Note on the Hawking-Penrose Controversy
Any theory that states that the basic laws of physics are time-symmetric must
be strictly deterministic. Only determinism enables time reversal of entropy
increase. A contradiction therefore arises between two statements of Hawking. A
simulation of a system under time reversal shows how an intrinsic time arrow
re-emerges, destroying the time reversal, when even slight failure of
determinism occurs.Comment: 9 pages, 4 figure
OH 1720 MHz Masers in Supernova Remnants --- C-Shock Indicators
Recent observations show that the OH 1720 MHz maser is a powerful probe of
the shocked region where a supernova remnant strikes a molecular cloud. We
perform a thorough study of the pumping of this maser and find tight
constraints on the physical conditions needed for its production. The presence
of the maser implies moderate temperatures (50 -- 125 K) and densities (), and OH column densities of order . We show
that these conditions can exist only if the shocks are of C-type. J-shocks fail
by such a wide margin that the presence of this maser could become the most
powerful indicator of C-shocks. These conditions also mean that the 1720 MHz
maser will be inherently weak compared to the other ground state OH masers. All
the model predictions are in good agreement with the observations.Comment: 16 pages, 5 Postscript figures (included), uses aaspp4.sty. To appear
in the Astrophysical Journa
On Induced Gravity in 2-d Topological Theories
We study 2-d gauge theories with the objective to understand, also
at the quantum level, the emergence of induced gravity. The wave functionals -
representing the eigenstates of a vanishing flat potential - are obtained in
the representation. The composition of the space they describe is then
analyzed: the state corresponding to the singlet representation of the gauge
group describes a topological universe. For other representations a metric
which is invariant under the residual gauge group is induced, apart from
possible topological obstructions. Being inherited from the group metric it is
rather rigid.Comment: 38, tex, 160/93/e
Analytical Results for Abelian Projection
Analytic methods for Abelian projection are developed, and a number of
results related to string tension measurements are obtained. It is proven that
even without gauge fixing, Abelian projection yields string tensions of the
underlying non-Abelian theory. Strong arguments are given for similar results
in the case where gauge fixing is employed. The subgroup used for projection
need only contain the center of the gauge group, and need not be Abelian. While
gauge fixing is shown to be in principle unnecessary for the success of Abelian
projection, it is computationally advantageous for the same reasons that
improved operators, e.g., the use of fat links, are advantageous in Wilson loop
measurements.Comment: LATTICE98(confine), 3 pages, 1 eps figur
Nonlocal Effects of Partial Measurements and Quantum Erasure
Partial measurement turns the initial superposition not into a definite
outcome but into a greater probability for it. The probability can approach
100%, yet the measurement can undergo complete quantum erasure. In the EPR
setting, we prove that i) every partial measurement nonlocally creates the same
partial change in the distant particle; and ii) every erasure inflicts the same
erasure on the distant particle's state. This enables an EPR experiment where
the nonlocal effect does not vanish after a single measurement but keeps
"traveling" back and forth between particles. We study an experiment in which
two distant particles are subjected to interferometry with a partial "which
path" measurement. Such a measurement causes a variable amount of correlation
between the particles. A new inequality is formulated for same-angle
polarizations, extending Bell's inequality for different angles. The resulting
nonlocality proof is highly visualizable, as it rests entirely on the
interference effect. Partial measurement also gives rise to a new form of
entanglement, where the particles manifest correlations of multiple
polarization directions. Another novelty in that the measurement to be erased
is fully observable, in contrast to prevailing erasure techniques where it can
never be observed. Some profound conceptual implications of our experiment are
briefly pointed out.Comment: To be published in Phys. Rev. A 63 (2001). 19 pages, 12 figures,
RevTeX 3.
The Nature of Deeply Buried Ultraluminous Infrared Galaxies: A Unified Model for Highly Obscured Dusty Galaxy Emission
We present models of deeply buried ultraluminous infrared galaxy (ULIRG)
spectral energy distributions (SEDs) and use them to construct a
three-dimensional diagram for diagnosing the nature of observed ULIRGs. Our
goal is to construct a suite of SEDs for a very simple model ULIRG structure,
and to explore how well this simple model can (by itself) explain the full
range of observed ULIRG properties. We use our diagnostic to analyze archival
Spitzer Space Telescope IRS spectra of ULIRGs and find that: (1) In general,
our model does provide a comprehensive explanation of the distribution of
mid-IR ULIRG properties; (2) >75% (in some cases 100%) of the bolometric
luminosities of the most deeply buried ULIRGs must be powered by a
dust-enshrouded active galactic nucleus; (3) an unobscured "keyhole" view
through <~10% of the obscuring medium surrounding a deeply buried ULIRG is
sufficient to make it appear nearly unobscured in the mid-IR; and (4) the
observed absence of deeply buried ULIRGs with large PAH equivalent widths is
naturally explained by our models showing that deep absorption features are
"filled-in" by small quantities of foreground unobscured PAH emission (e.g.,
from the host galaxy disk) at the level of ~1% the bolometric nuclear
luminosity. The modeling and analysis we present will also serve as a powerful
tool for interpreting the high angular resolution spectra of high-redshift
sources to be obtained with the James Webb Space Telescope.Comment: 20 pages, 14 figures. Accepted for publication in the Ap
Type I Superconductivity upon Monopole Condensation in Seiberg-Witten Theory
We study the confinement scenario in N=2 supersymmetric SU(2) gauge theory
near the monopole point upon breaking of N=2 supersymmetry by the adjoint
matter mass term. We confirm claims made previously that the
Abrikosov-Nielsen-Olesen string near the monopole point fails to be a BPS state
once next-to-leading corrections in the adjoint mass parameter taken into
account. Our results shows that type I superconductivity arises upon monopole
condensation. This conclusion allows us to make qualitative predictions on the
structure of the hadron mass spectrum near the monopole point.Comment: LaTex, 25 pages. Minor changes. To be published in NP
Fractional Branes, Confinement, and Dynamically Generated Superpotentials
We examine the effects of instantons in four dimensional N=1 supersymmetric
gauge theory by including D0-branes in type IIA brane constructions. We examine
instanton generated superpotentials in supersymmetric QCD and find that they
are due to a repulsive force between D4-branes bound to D0-branes ending on NS
5-branes. We study situations where instanton effects break supersymmetry such
as the Intriligator-Thomas-Izawa-Yangagida model and relate this to a IIA brane
construction. We also argue how confinement due to a condensate of fractional
instantons manifests itself in Super Yang-Mills theory using fractional D0
branes, D4 branes, and NS strings.Comment: 19 pages, 2 figures, uses harvmac. References adde
Lattice Supersymmetry and Topological Field Theory
It is known that certain theories with extended supersymmetry can be
discretized in such a way as to preserve an exact fermionic symmetry. In the
simplest model of this kind, we show that this residual supersymmetric
invariance is actually a BRST symmetry associated with gauge fixing an
underlying local shift symmetry. Furthermore, the starting lattice action is
then seen to be entirely a gauge fixing term. The corresponding continuum
theory is known to be a topological field theory. We look, in detail, at one
example - supersymmetric quantum mechanics which possesses two such BRST
symmetries. In this case, we show that the lattice theory can be obtained by
blocking out of the continuum in a carefully chosen background metric. Such a
procedure will not change the Ward identities corresponding to the BRST
symmetries since they correspond to topological observables. Thus, at the
quantum level, the continuum BRST symmetry is preserved in the lattice theory.
Similar conclusions are reached for the two-dimensional complex Wess-Zumino
model and imply that all the supersymmetric Ward identities are satisfied {\it
exactly} on the lattice. Numerical results supporting these conclusions are
presented.Comment: 18 pages, 2 figure
On rolling, tunneling and decaying in some large N vector models
Various aspects of time-dependent processes are studied within the large N
approximation of O(N) vector models in three dimensions. These include the
rolling of fields, the tunneling and decay of vacua. We present an exact
solution for the quantum conformal case and find a solution for more general
potentials when the total change of the value of the field is small.
Characteristic times are found to be shorter when the time dependence of the
field is taken into account in constructing the exact large N effective
potentials. We show that the different approximations yield the same answers in
the regions of the overlap of the validity. A numerical solution of this
potential reveals a tunneling in which the bubble that separates the true
vacuum from the false one is thick
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