1,160 research outputs found
Alternative symplectic structures for SO(3,1) and SO(4) four-dimensional BF theories
The most general action, quadratic in the B fields as well as in the
curvature F, having SO(3,1) or SO(4) as the internal gauge group for a
four-dimensional BF theory is presented and its symplectic geometry is
displayed. It is shown that the space of solutions to the equations of motion
for the BF theory can be endowed with symplectic structures alternative to the
usual one. The analysis also includes topological terms and cosmological
constant. The implications of this fact for gravity are briefly discussed.Comment: 13 pages, LaTeX file, no figure
Geometric thermodynamics: black holes and the meaning of the scalar curvature
In this paper we show that the vanishing of the scalar curvature of
Ruppeiner-like metrics does not characterize the ideal gas. Furthermore, we
claim through an example that flatness is not a sufficient condition to
establish the absence of interactions in the underlying microscopic model of a
thermodynamic system, which poses a limitation on the usefulness of Ruppeiner's
metric and conjecture. Finally, we address the problem of the choice of
coordinates in black hole thermodynamics. We propose an alternative energy
representation for Kerr-Newman black holes that mimics fully Weinhold's
approach. The corresponding Ruppeiner's metrics become degenerate only at
absolute zero and have non-vanishing scalar curvatures.Comment: LaTeX file, no figure
Real sector of the nonminimally coupled scalar field to self-dual gravity
A scalar field nonminimally coupled to gravity is studied in the canonical
framework, using self-dual variables. The corresponding constraints are first
class and polynomial. To identify the real sector of the theory, reality
conditions are implemented as second class constraints, leading to three real
configurational degrees of freedom per space point. Nevertheless, this
realization makes non-polynomial some of the constraints. The original complex
symplectic structure reduces to the expected real one, by using the appropriate
Dirac brackets. For the sake of preserving the simplicity of the constraints,
an alternative method preventing the use of Dirac brackets, is discussed. It
consists of converting all second class constraints into first class by adding
extra variables. This strategy is implemented for the pure gravity case.Comment: Latex file, 22 pages, no figure
Evidence for a circumplanetary disk around protoplanet PDS 70 b
We present the first observational evidence for a circumplanetary disk around
the protoplanet PDS~70~b, based on a new spectrum in the band acquired with
VLT/SINFONI. We tested three hypotheses to explain the spectrum: Atmospheric
emission from the planet with either (1) a single value of extinction or (2)
variable extinction, and (3) a combined atmospheric and circumplanetary disk
model. Goodness-of-fit indicators favour the third option, suggesting
circumplanetary material contributing excess thermal emission --- most
prominent at m. Inferred accretion rates (-- yr) are compatible with observational
constraints based on the H and Br lines. For the planet, we
derive an effective temperature of 1500--1600 K, surface gravity , radius , mass , and possible thick clouds.
Models with variable extinction lead to slightly worse fits. However, the
amplitude (mag) and timescale of variation
(~years) required for the extinction would also suggest
circumplanetary material.Comment: 8 pages, 2 figures, 1 table. This is a pre-copyedited,
author-produced PDF of an article accepted for publication in ApJL on 2019
May 1
HD 169142 in the eyes of ZIMPOL/SPHERE
We present new data of the protoplanetary disc surrounding the Herbig Ae/Be
star HD 169142 obtained in the very broad-band (VBB) with the Zurich imaging
polarimeter (ZIMPOL), a sub-system of the Spectro-Polarimetric High-contrast
Exoplanet REsearch instrument (SPHERE) at the Very Large Telescope (VLT). Our
Polarimetric Differential Imaging (PDI) observations probe the disc as close as
0.03" (3.5au) to the star and are able to trace the disc out to ~1.08"
(~126au). We find an inner hole, a bright ring bearing substructures around
0.18" (21au), and an elliptically shaped gap stretching from 0.25" to 0.47"
(29-55au). Outside of 0.47", the surface brightness drops off, discontinued
only by a narrow annular brightness minimum at ~0.63"-0.74" (74-87au). These
observations confirm features found in less-well resolved data as well as
reveal yet undetected indications for planet-disc interactions, such as
small-scale structures, star-disk offsets, and potentially moving shadows.Comment: Accepted for publication in MNRA
VocaLiST: An Audio-Visual Synchronisation Model for Lips and Voices
In this paper, we address the problem of lip-voice synchronisation in videos
containing human face and voice. Our approach is based on determining if the
lips motion and the voice in a video are synchronised or not, depending on
their audio-visual correspondence score. We propose an audio-visual cross-modal
transformer-based model that outperforms several baseline models in the
audio-visual synchronisation task on the standard lip-reading speech benchmark
dataset LRS2. While the existing methods focus mainly on the lip
synchronisation in speech videos, we also consider the special case of singing
voice. Singing voice is a more challenging use case for synchronisation due to
sustained vowel sounds. We also investigate the relevance of lip
synchronisation models trained on speech datasets in the context of singing
voice. Finally, we use the frozen visual features learned by our lip
synchronisation model in the singing voice separation task to outperform a
baseline audio-visual model which was trained end-to-end. The demos, source
code, and the pre-trained model will be made available on
https://ipcv.github.io/VocaLiST/Comment: Submitted to Interspeech 2022; Project Page:
https://ipcv.github.io/VocaLiST
A new look inside Planetary Nebula LoTr 5: A long-period binary with hints of a possible third component
LoTr 5 is a planetary nebula with an unusual long-period binary central star.
As far as we know, the pair consists of a rapidly rotating G-type star and a
hot star, which is responsible for the ionization of the nebula. The rotation
period of the G-type star is 5.95 days and the orbital period of the binary is
now known to be 2700 days, one of the longest in central star of
planetary nebulae. The spectrum of the G central star shows a complex H
double-peaked profile which varies with very short time scales, also reported
in other central stars of planetary nebulae and whose origin is still unknown.
We present new radial velocity observations of the central star which allow us
to confirm the orbital period for the long-period binary and discuss the
possibility of a third component in the system at 129 days to the G star.
This is complemented with the analysis of archival light curves from SuperWASP,
ASAS and OMC. From the spectral fitting of the G-type star, we obtain a
effective temperature of = 5410250 K and surface gravity of
= 2.70.5, consistent with both giant and subgiant stars. We also
present a detailed analysis of the H double-peaked profile and conclude
that it does not present correlation with the rotation period and that the
presence of an accretion disk via Roche lobe overflow is unlikely.Comment: 12 pages, 12 figures, accepted for publication in MNRA
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