8,113 research outputs found
Complements of tori and Klein bottles in the 4-sphere that have hyperbolic structure
Many noncompact hyperbolic 3-manifolds are topologically complements of links
in the 3-sphere. Generalizing to dimension 4, we construct a dozen examples of
noncompact hyperbolic 4-manifolds, all of which are topologically complements
of varying numbers of tori and Klein bottles in the 4-sphere. Finite covers of
some of those manifolds are then shown to be complements of tori and Klein
bottles in other simply-connected closed 4-manifolds. All the examples are
based on a construction of Ratcliffe and Tschantz, who produced 1171 noncompact
hyperbolic 4-manifolds of minimal volume. Our examples are finite covers of
some of those manifolds.Comment: Published by Algebraic and Geometric Topology at
http://www.maths.warwick.ac.uk/agt/AGTVol5/agt-5-41.abs.htm
Late-time structure of the Bunch-Davies de Sitter wavefunction
We examine the late time behavior of the Bunch-Davies wavefunction for interacting light fields in a de Sitter background. We use perturbative techniques developed in the framework of AdS/CFT, and analytically continue to compute tree and loop level contributions to the Bunch-Davies wavefunction. We consider self-interacting scalars of general mass, but focus especially on the massless and conformally coupled cases. We show that certain contributions grow logarithmically in conformal time both at tree and loop level. We also consider gauge fields and gravitons. The four-dimensional Fefferman-Graham expansion of classical asymptotically de Sitter solutions is used to show that the wavefunction contains no logarithmic growth in the pure graviton sector at tree level. Finally, assuming a holographic relation between the wavefunction and the partition function of a conformal field theory, we interpret the logarithmic growths in the language of conformal field theory
The Three Loop Equation of State of QED at High Temperature
We present the three loop contribution (order ) to the pressure of
massless quantum electrodynamics at nonzero temperature. The calculation is
performed within the imaginary time formalism. Dimensional regularization is
used to handle the usual, intermediate stage, ultraviolet and infrared
singularities, and also to prevent overcounting of diagrams during resummation.Comment: ANL-HEP-PR-94-02, SPhT/94-054 (revised final version
Holographic Normal Ordering and Multi-particle States in the AdS/CFT Correspondence
The general correlator of composite operators of N=4 supersymmetric gauge
field theory is divergent. We introduce a means for renormalizing these
correlators by adding a boundary theory on the AdS space correcting for the
divergences. Such renormalizations are not equivalent to the standard normal
ordering of current algebras in two dimensions. The correlators contain contact
terms that contribute to the OPE; we relate them diagrammatically to
correlation functions of compound composite operators dual to multi-particle
states.Comment: 18 pages, one equation corr., further comments and refs. adde
New Results of Observations of the Only Supernova Remnant in the IC1613 Galaxy
The new results of a study of the kinematics of the supernova remnant S8 in
the IC1613 galaxy are reported. The expansion velocity of the bright optical
nebula is determined based on observations made with the 6-m telescope of the
Special Astrophysical Observatory of the Russian Academy of Sciences using MPSF
field spectrograph and SCORPIO focal reducer operating in the scanning
Fabry--Perot interferometer mode. An analysis of 21-cm line VLA observations of
the galaxy corroborates our earlier proposed model of a SN exploding inside a
cavern surrounded by a dense shell and S8 colliding with the wall of the HI
shell.Comment: 8 pages, 7 figures; accepted for publication in Astronomy Letter
Ammonia as a tracer of chemical equilibrium in the T7.5 dwarf Gliese 570D
We present the first analysis of an optical to mid-infrared spectrum of the
T7.5 dwarf Gliese 570D with model atmospheres, synthetic spectra, and brown
dwarf evolution sequences. We obtain precise values for the basic parameters of
Gl 570D: Teff=800 - 820K, log g (cm/s^2)=5.09 - 5.23, and log L/Lsun= -5.525 to
-5.551. The Spitzer IRS spectrum shows prominent features of ammonia (NH3) that
can only be fitted by reducing the abundance of NH3 by about one order of
magnitude from the value obtained with chemical equilibrium models. We model
departures from chemical equilibrium in the atmosphere of Gl 570D by
considering the kinetics of nitrogen and carbon chemistry in the presence of
vertical mixing. The resulting model spectrum reproduces the data very well.Comment: Accepted for publication in the ApJ. 10 pages, including 3 figure
Improved Thermoelectric Cooling Based on the Thomson Effect
Traditional thermoelectric Peltier coolers exhibit a cooling limit which is
primarily determined by the figure of merit, zT. Rather than a fundamental
thermodynamic limit, this bound can be traced to the difficulty of maintaining
thermoelectric compatibility. Self-compatibility locally maximizes the cooler's
coefficient of performance for a given zT and can be achieved by adjusting the
relative ratio of the thermoelectric transport properties that make up zT. In
this study, we investigate the theoretical performance of thermoelectric
coolers that maintain self-compatibility across the device. We find such a
device behaves very differently from a Peltier cooler, and term self-compatible
coolers "Thomson coolers" when the Fourier heat divergence is dominated by the
Thomson, as opposed to the Joule, term. A Thomson cooler requires an
exponentially rising Seebeck coefficient with increasing temperature, while
traditional Peltier coolers, such as those used commercially, have
comparatively minimal change in Seebeck coefficient with temperature. When
reasonable material property bounds are placed on the thermoelectric leg, the
Thomson cooler is predicted to achieve approximately twice the maximum
temperature drop of a traditional Peltier cooler with equivalent figure of
merit (zT). We anticipate the development of Thomson coolers will ultimately
lead to solid state cooling to cryogenic temperatures.Comment: The Manuscript has been revised for publication in PR
Calibration of the distance scale from galactic Cepheids: I Calibration based on the GFG sample
New estimates of the distances of 36 nearby galaxies are presented based on
accurate distances of galactic Cepheids obtained by Gieren, Fouque and Gomez
(1998) from the geometrical Barnes-Evans method.
The concept of 'sosie' is applied to extend the distance determination to
extragalactic Cepheids without assuming the linearity of the PL relation. Doing
so, the distance moduli are obtained in a straightforward way.
The correction for extinction is made using two photometric bands (V and I)
according to the principles introduced by Freedman and Madore (1990). Finally,
the statistical bias due to the incompleteness of the sample is corrected
according to the precepts introduced by Teerikorpi (1987) without introducing
any free parameters (except the distance modulus itself in an iterative
scheme).
The final distance moduli depend on the adopted extinction ratio {R_V}/{R_I}
and on the limiting apparent magnitude of the sample. A comparison with the
distance moduli recently published by the Hubble Space Telescope Key Project
(HSTKP) team reveals a fair agreement when the same ratio {R_V}/{R_I} is used
but shows a small discrepancy at large distance.
In order to bypass the uncertainty due to the metallicity effect it is
suggested to consider only galaxies having nearly the same metallicity as the
calibrating Cepheids (i.e. Solar metallicity). The internal uncertainty of the
distances is about 0.1 magnitude but the total uncertainty may reach 0.3
magnitude.Comment: 12 pages, 4 figures, access to a database of extragalactic Cepheids.
Astronomy & Astrophysics (in press) 200
Sum rules and three point functions
Sum rules constraining the R-current spectral densities are derived
holographically for the case of D3-branes, M2-branes and M5-branes all at
finite chemical potentials. In each of the cases the sum rule relates a certain
integral of the spectral density over the frequency to terms which depend both
on long distance physics, hydrodynamics and short distance physics of the
theory. The terms which which depend on the short distance physics result from
the presence of certain chiral primaries in the OPE of two R-currents which are
turned on at finite chemical potential. Since these sum rules contain
information of the OPE they provide an alternate method to obtain the structure
constants of the two R-currents and the chiral primary. As a consistency check
we show that the 3 point function derived from the sum rule precisely matches
with that obtained using Witten diagrams.Comment: 41 page
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