73,540 research outputs found
The spectral problem of the ABJ Fermi gas
The partition function on the three-sphere of ABJ theory can be rewritten
into a partition function of a non-interacting Fermi gas, with an accompanying
one-particle Hamiltonian. We study the spectral problem defined by this
Hamiltonian. We determine the exact WKB quantization condition, which involves
quantities from refined topological string theory, and test it successfully
against numerical calculations of the spectrum.Comment: 31 page
Lectures on the topological recursion for Higgs bundles and quantum curves
© 2018 World Scientific Publishing Co. Pte. Ltd. This chapter aims at giving an introduction to the notion of quantum curves. The main purpose is to describe the new discovery of the relation between the following two disparate subjects: one is the topological recursion, that has its origin in random matrix theory and has been effectively applied to many enumerative geometry problems; and the other is the quantization of Hitchin spectral curves associated with Higgs bundles. Our emphasis is on explaining the motivation and examples. Concrete examples of the direct relation between Hitchin spectral curves and enumeration problems are given. A general geometric framework of quantum curves is also discussed
A Volume-limited Sample of 63 M7-M9.5 Dwarfs II. Activity, magnetism, and the fade of the rotation-dominated dynamo
In a volume-limited sample of 63 ultracool dwarfs of spectral type M7-M9.5,
we have obtained high-resolution spectroscopy with UVES at the Very Large
Telescope and HIRES at Keck Observatory. In this second paper, we present
projected rotation velocities, average magnetic field strengths, and
chromospheric emission from the Halpha line. We confirm earlier results that
the mean level of normalized Halpha luminosity decreases with lower
temperature, and we find that the scatter among Halpha luminosities is larger
at lower temperature. We measure average magnetic fields between 0 and 4kG with
no indication for a dependence on temperature between M7 and M9.5. For a given
temperature, Halpha luminosity is related to magnetic field strength,
consistent with results in earlier stars. A few very slowly rotating stars show
very weak magnetic fields and Halpha emission, all stars rotating faster than
our detection limit show magnetic fields of at least a few hundred Gauss. In
contrast to earlier-type stars, we observe magnetic fields weaker than 1kG in
stars rotating faster than ~3km/s, but we find no correlation between rotation
and magnetic flux generation among them. We interpret this as a fundamental
change in the dynamo mechanism; in ultracool dwarfs, magnetic field generation
is predominantly achieved by a turbulent dynamo, while other mechanisms can
operate more efficiently at earlier spectral type.Comment: accepted by Ap
The Bulk Channel in Thermal Gauge Theories
We investigate the thermal correlator of the trace of the energy-momentum
tensor in the SU(3) Yang-Mills theory. Our goal is to constrain the spectral
function in that channel, whose low-frequency part determines the bulk
viscosity. We focus on the thermal modification of the spectral function,
. Using the operator-product expansion we give
the high-frequency behavior of this difference in terms of thermodynamic
potentials. We take into account the presence of an exact delta function
located at the origin, which had been missed in previous analyses. We then
combine the bulk sum rule and a Monte-Carlo evaluation of the Euclidean
correlator to determine the intervals of frequency where the spectral density
is enhanced or depleted by thermal effects. We find evidence that the thermal
spectral density is non-zero for frequencies below the scalar glueball mass
and is significantly depleted for .Comment: (1+25) pages, 6 figure
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