8,278 research outputs found
A reciprocity formula from abelian BF and Turaev-Viro theories
In this article we show that the use of Deligne-Beilinson cohomology in the
context of the BF theory on a closed 3-manifold yields a discrete
BF theory whose partition function is an abelian TV invariant of . By
comparing the expectation values of the and holonomies in
both BF theories we obtain a reciprocity formula
- Glueball Spectrum within a Constituent Picture
The quantum numbers and mass hierarchy of the glueballs observed in
-dimensional lattice QCD with gauge group SU() are shown to be in
agreement with a constituent picture. The agreement is maintained when going
from glueballs to gluelumps, and when the gauge group SO() is taken
instead of SU()
String deformations induced by retardation effects
The rotating string model is an effective model of mesons, in which the quark
and the antiquark are linked by a straight string. We previously developed a
new framework to include the retardation effects in the rotating string model,
but the string was still kept straight. We now go a step further and show that
the retardation effects cause a small deviation of the string from the straight
line. We first give general arguments constraining the string shape. Then, we
find analytical and numerical solutions for the string deformation induced by
retardation effects. We finally discuss the influence of the curved string on
the energy spectrum of the model.Comment: 3 figure
Recognizing well-parenthesized expressions in the streaming model
Motivated by a concrete problem and with the goal of understanding the sense
in which the complexity of streaming algorithms is related to the complexity of
formal languages, we investigate the problem Dyck(s) of checking matching
parentheses, with different types of parenthesis.
We present a one-pass randomized streaming algorithm for Dyck(2) with space
\Order(\sqrt{n}\log n), time per letter \polylog (n), and one-sided error.
We prove that this one-pass algorithm is optimal, up to a \polylog n factor,
even when two-sided error is allowed. For the lower bound, we prove a direct
sum result on hard instances by following the "information cost" approach, but
with a few twists. Indeed, we play a subtle game between public and private
coins. This mixture between public and private coins results from a balancing
act between the direct sum result and a combinatorial lower bound for the base
case.
Surprisingly, the space requirement shrinks drastically if we have access to
the input stream in reverse. We present a two-pass randomized streaming
algorithm for Dyck(2) with space \Order((\log n)^2), time \polylog (n) and
one-sided error, where the second pass is in the reverse direction. Both
algorithms can be extended to Dyck(s) since this problem is reducible to
Dyck(2) for a suitable notion of reduction in the streaming model.Comment: 20 pages, 5 figure
X rays from old open clusters: M 67 and NGC 188
We have observed the old open clusters M 67 and NGC 188 with the ROSAT PSPC.
In M 67 we detect a variety of X-ray sources. The X-ray emission by a
cataclysmic variable, a single hot white dwarf, two contact binaries, and some
RS CVn systems is as expected. The X-ray emission by two binaries located below
the subgiant branch in the Hertzsprung Russell diagram of the cluster, by a
circular binary with a cool white dwarf, and by two eccentric binaries with
orbital period > 700 d is puzzling. Two members of NGC 188 are detected,
including the FK Com type star D719. Another possible FK Com type star,
probably not a member of NGC 188, is also detected.Comment: 10 pages, 5 figures. Accepted for publication on Astronomy &
Astrophysic
Constituent gluon interpretation of glueballs and gluelumps
Arguments are given that support the interpretation of the lattice QCD
glueball and gluelump spectra in terms of bound states of massless constituent
gluons with helicity-1. In this scheme, the mass hierarchy of the currently
known gluelumps and glueballs is mainly due to the number of constituent gluons
and can be understood within a simple flux tube model. It is also argued that
the lattice QCD glueball should be seen as a four-gluon bound state.
The flux tube model allows for a parameter-free computation of its mass, which
is in good agreement with lattice QCD.Comment: 3 figures, use of package youngta
Characters of graded parafermion conformal field theory
The graded parafermion conformal field theory at level k is a close cousin of
the much-studied Z_k parafermion model. Three character formulas for the graded
parafermion theory are presented, one bosonic, one fermionic (both previously
known) and one of spinon type (which is new). The main result of this paper is
a proof of the equivalence of these three forms using q-series methods combined
with the combinatorics of lattice paths. The pivotal step in our approach is
the observation that the graded parafermion theory -- which is equivalent to
the coset osp(1,2)_k/ u(1) -- can be factored as (osp(1,2)_k/ su(2)_k) x
(su(2)_k/ u(1)), with the two cosets on the right equivalent to the minimal
model M(k+2,2k+3) and the Z_k parafermion model, respectively. This
factorisation allows for a new combinatorial description of the graded
parafermion characters in terms of the one-dimensional configuration sums of
the (k+1)-state Andrews--Baxter--Forrester model.Comment: 36 page
Probing Quantum Optical Excitations with Fast Electrons
Probing optical excitations with nanometer resolution is important for
understanding their dynamics and interactions down to the atomic scale.
Electron microscopes currently offer the unparalleled ability of rendering
spatially-resolved electron spectra with combined meV and sub-nm resolution,
while the use of ultrafast optical pulses enables fs temporal resolution and
exposure of the electrons to ultraintense confined optical fields. Here, we
theoretically investigate fundamental aspects of the interaction of fast
electrons with localized optical modes that are made possible by these
advances. We use a quantum-optics description of the optical field to predict
that the resulting electron spectra strongly depend on the statistics of the
sample excitations (bosonic or fermionic) and their population (Fock, coherent,
or thermal), whose autocorrelation functions are directly retrieved from the
ratios of electron gain intensities. We further explore feasible experimental
scenarios to probe the quantum characteristics of the sampled excitations and
their populations.Comment: 13 pages, 6 figures, 56 reference
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