371 research outputs found
Holographic Non-equilibrium Heating
We study the holographic entanglement entropy evolution after a global sharp
quench of thermal state. After the quench, the system comes to equilibrium and
the temperature increases from to . Holographic dual of this process
is provided by an injection of a thin shell of matter in the black hole
background. The quantitative characteristics of the evolution depend
substantially on the size of the initial black hole. We show that
characteristic regimes during non-equilibrium heating do not depend on the
initial temperature and are the same as in thermalization. Namely these regimes
are pre-local-equilibration quadratic growth, linear growth and saturation
regimes of the time evolution of the holographic entanglement entropy. We study
the initial temperature dependence of quantitative characteristics of these
regimes and find that the critical exponents do not depend on the temperature,
meanwhile the prefactors are the functions on the temperature.Comment: v1:12 pages, 9 figures; v2:The title and abstract are slightly
changed, the discussion is enlarged, the pictures are changed to make
presentation more clear and refs. added , 22 pages, 4 figures; v3: typos
correcte
Have Pentaquark States Been seen?
The status of the search for pentaquark baryons is reviewed in light of new
results from the first two dedicated experiments from CLAS at Jefferson Lab and
of new analyses from several laboratories on the . Evidence for
and against two heavier pentaquark states is also discussed.Comment: Added some references, corrected typo
The Covering Homotopy Extension Problem for Compact Transformation Groups
It is shown that the orbit space of universal (in the sense of Palais) G-spaces classifies G-spaces. Theorems on the extension of covering homotopy for G-spaces and on a homotopy representation of the isovariant category ISOV are proved
Preserving -sets by Dranishnikov's resolution
We prove that Dranishnikov's -dimensional resolution is a UV-divider of Chigogidze's -dimensional resolution .
This fact implies that preserves -sets. A further development of
the concept of UV-dividers permits us to find sufficient conditions for
to be homeomorphic to the N\"{o}beling space or the
universal pseudoboundary . We also obtain some other applications
Spin and orbital angular momentum of the proton
Since the announcement of the proton spin crisis by the European Muon
Collaboration there has been considerable progress in unravelling the
distribution of spin and orbital angular momentum within the proton. We review
the current status of the problem, showing that not only have strong upper
limits have been placed on the amount of polarized glue in the proton but that
the experimental determination of the spin content has become much more
precise. It is now clear that the origin of the discrepancy between experiment
and the naive expectation of the fraction of spin carried by the quarks and
anti-quarks in the proton lies in the non-perturbative structure of the proton.
We explain how the features expected in a modern, relativistic and chirally
symmetric description of nucleon structure naturally explain the current data.
The consequences of this explanation for the presence of orbital angular
momentum on quarks and gluons is reviewed and comparison made with recent
results from lattice QCD and experimental data.Comment: Lectures at Aligarh University (4th DAE-BRNS Workshop on Hadron
Physics, Feb 18-21, 200
Entanglement entropy in de Sitter: no pure states for conformal matter
In this paper, we consider the entanglement entropy of conformal matter for
finite and semi-infinite entangling regions, as well as the formation of
entanglement islands in four-dimensional de Sitter spacetime partially reduced
to two dimensions. We analyze complementarity and pure state condition of the
entanglement entropy of pure states and show that they never hold in the given
setup. We consider two different types of Cauchy surfaces in the extended
static patch and flat coordinates, correspondingly. For former, we found that
entanglement entropy of a pure state is always bounded from below by a constant
and never becomes zero, as required by quantum mechanics. In turn, the
difference between the entropies for some region and its complement, which
should be zero for a pure state, in direct calculations essentially depends on
how the boundaries of these regions evolve with time. Regarding the flat
coordinates, it is impossible to regularize spacelike infinity in a way that
would be compatible with complementarity and pure state condition, as opposed,
for instance, to two-sided Schwarzschild black hole. Finally, we discuss the
information paradox in de Sitter and show that the island formula does not
resolve it. Namely, we give examples of a region with a time-limited growth of
entanglement entropy, for which there is no island solution, and the region,
for which entanglement entropy does not grow, but the island solution exists.Comment: v1: 25 pages, 10 figures; v2: 25 pages, 10 figures, references added,
notation clarifie
Stable marriage and roommates problems with restricted edges: complexity and approximability
In the Stable Marriage and Roommates problems, a set of agents is given, each of them having a strictly ordered preference list over some or all of the other agents. A matching is a set of disjoint pairs of mutually acceptable agents. If any two agents mutually prefer each other to their partner, then they block the matching, otherwise, the matching is said to be stable. We investigate the complexity of finding a solution satisfying additional constraints on restricted pairs of agents. Restricted pairs can be either forced or forbidden. A stable solution must contain all of the forced pairs, while it must contain none of the forbidden pairs.
Dias et al. (2003) gave a polynomial-time algorithm to decide whether such a solution exists in the presence of restricted edges. If the answer is no, one might look for a solution close to optimal. Since optimality in this context means that the matching is stable and satisfies all constraints on restricted pairs, there are two ways of relaxing the constraints by permitting a solution to: (1) be blocked by as few as possible pairs, or (2) violate as few as possible constraints n restricted pairs.
Our main theorems prove that for the (bipartite) Stable Marriage problem, case (1) leads to View the MathML source-hardness and inapproximability results, whilst case (2) can be solved in polynomial time. For non-bipartite Stable Roommates instances, case (2) yields an View the MathML source-hard but (under some cardinality assumptions) 2-approximable problem. In the case of View the MathML source-hard problems, we also discuss polynomially solvable special cases, arising from restrictions on the lengths of the preference lists, or upper bounds on the numbers of restricted pairs
Entanglement Islands and Infrared Anomalies in Schwarzschild Black Hole
In this paper, island formation for entangling regions of finite size in the
asymptotically flat eternal Schwarzschild black hole is considered. We check
the complementarity property of entanglement entropy which was implicitly
assumed in previous studies for semi-infinite regions. This check reveals the
emergence of infrared anomalies after regularization of a Cauchy surface. A
naive infrared regularization based on ``mirror symmetry'' is considered and
its failure is shown. We introduce an improved regularization that gives a
correct limit agreed with the semi-infinite results from previous studies. As
the time evolution goes, the endpoints of a finite region compatible with the
improved regularization become separated by a timelike interval. We call this
phenomenon the ``Cauchy surface breaking''. Shortly before the Cauchy surface
breaking, finite size configurations generate asymmetric entanglement islands
in contrast to the semi-infinite case. Depending on the size of the finite
regions, qualitatively new behaviour arises, such as discontinuous evolution of
the entanglement entropy and the absence of island formation. Finally, we show
that the island prescription does not help us to solve the information paradox
for certain finite size regions.Comment: v1: 55 pages, 19 figures; v2: 57 pages, 19 figures, references added,
Sec. 5 presentation improve
Very high quality factor measured in annealed fused silica
We present the results of quality factor measurements for rod samples made of
fused silica. To decrease the dissipation we annealed our samples. The highest
quality factor that we observed was for a mode at
384 Hz. This is the highest published value of in fused silica measured to
date.Comment: 8 pages, 2 figure
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