965 research outputs found
BRST Analysis of Physical Fields and States for 4D Quantum Gravity on R x S^3
We consider the background-free quantum gravity based on conformal gravity
with the Riegert-Wess-Zumino action, which is formulated in terms of a
conformal field theory. Employing the background in practice, we
construct the nilpotent BRST operator imposing diffeomorphism invariance.
Physical fields and states are analyzed, which are given only by real primary
scalars with a definite conformal weight. With attention to the presence of
background charges, various significant properties, such as the state-operator
correspondence and the norm structure, are clarified with some examples.Comment: 29 pages, several descriptions written using CFT terminology are
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The expressions for the 2nd-order mixed partial derivatives of Slater-Koster matrix elements at spherical coordinate singularities
In a recent publication it has been shown how to generate derivatives with
respect to atom coordinates of Slater-Koster matrix elements for the tight
binding (TB) modelling of a system. For the special case of a mixed second
partial derivative at coordinate singularities only the results were stated in
that publication. In this work, the derivation of these results is given in
detail. Though it may seem rather `technical' and only applicable to a very
special case, atomic configurations where the connecting vector between the two
atoms involved in a two-centre matrix element is aligned along the z-axis (in
the usual approach) require results for precisely this case. The expressions
derived in this work have been implemented in the DINAMO code.Comment: 9 pages, no figure
The Odd-Parity CMB Bispectrum
Measurement of the cosmic microwave background (CMB) bispectrum, or
three-point correlation function, has now become one of the principle efforts
in early-Universe cosmology. Here we show that there is a odd-parity component
of the CMB bispectrum that has been hitherto unexplored. We argue that
odd-parity temperature-polarization bispectra can arise, in principle, through
weak lensing of the CMB by chiral gravitational waves or through cosmological
birefringence, although the signals will be small even in the best-case
scenarios. Measurement of these bispectra requires only modest modifications to
the usual data-analysis algorithms. They may be useful as a consistency test in
searches for the usual bispectrum and to search for surprises in the data.Comment: 5 pages, 1 figur
Does the proton-to-electron mass ratio vary in the course of cosmological evolution?
The possible cosmological variation of the proton-to-electron mass ratio was
estimated by measuring the H_2 wavelengths in the high-resolution spectrum of
the quasar Q~0347-382. Our analysis yielded an estimate for the possible
deviation of \mu value in the past, 10 Gyr ago: for the unweighted value
; for the weighted value Since the significance of the both
results does not exceed 3, further observations are needed to increase
the statistical significance. In any case, this result may be considered as the
most stringent estimate on an upper limit of a possible variation of \mu (95%
C.L.): This value serves as an
effective tool for selection of models determining a relation between possible
cosmological deviations of the fine-structure constant \alpha and the
elementary particle masses (m, m, etc.).Comment: 6 pages, 1 figure. Talk presented at the JENAM 2002 Workshop on
Varying Fundamental Constants, Porto, 4th September 2002. To be published in
the Conference Proceeding
Testing cosmological variability of fundamental constants
One of the topical problems of contemporary physics is a possible variability
of the fundamental constants. Here we consider possible variability of two
dimensionless constants which are most important for calculation of atomic and
molecular spectra (in particular, the X-ray ones): the fine-structure constant
\alpha=e^2/\hbar c and the proton-to-electron mass ratio \mu=m_p/m_e. Values of
the physical constants in the early epochs are estimated directly from
observations of quasars - the most powerful sources of radiation, whose spectra
were formed when the Universe was several times younger than now. A critical
analysis of the available results leads to the conclusion that present-day data
do not reveal any statistically significant evidence for variations of the
fundamental constants under study. The most reliable upper limits to possible
variation rates at the 95% confidence level, obtained in our work, read:
|\dot\alpha/\alpha| < (1.4e-14)/yr,
|\dot\mu/\mu| < (1.5e-14)/yr
on the average over the last ten billion years.Comment: 9 pages, 2 figures, 2 tables, LaTeX using aipproc.sty (included). In:
X-ray and Inner-Shell Processes, R.W. Dunford, D.S. Gemmel, E.P. Kanter, B.
Kraessig, S.H. Southworth, L. Young (eds.), AIP Conf. Proc. (AIP, Melville,
2000) vol. 506, p. 50
Asymmetric Beams and CMB Statistical Anisotropy
Beam asymmetries result in statistically-anisotropic cosmic microwave
background (CMB) maps. Typically, they are studied for their effects on the CMB
power spectrum, however they more closely mimic anisotropic effects such as
gravitational lensing and primordial power asymmetry. We discuss tools for
studying the effects of beam asymmetry on general quadratic estimators of
anisotropy, analytically for full-sky observations as well as in the analysis
of realistic data. We demonstrate this methodology in application to a
recently-detected 9 sigma quadrupolar modulation effect in the WMAP data,
showing that beams provide a complete and sufficient explanation for the
anomaly.Comment: updated to match PRD version + typo correction in Eq. B
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