29,336 research outputs found
Graphical description of local Gaussian operations for continuous-variable weighted graph states
The form of a local Clifford (LC, also called local Gaussian (LG)) operation
for the continuous-variable (CV) weighted graph states is presented in this
paper, which is the counterpart of the LC operation of local complementation
for qubit graph states. The novel property of the CV weighted graph states is
shown, which can be expressed by the stabilizer formalism. It is distinctively
different from the qubit weighted graph states, which can not be expressed by
the stabilizer formalism. The corresponding graph rule, stated in purely graph
theoretical terms, is described, which completely characterizes the evolution
of CV weighted graph states under this LC operation. This LC operation may be
applied repeatedly on a CV weighted graph state, which can generate the
infinite LC equivalent graph states of this graph state. This work is an
important step to characterize the LC equivalence class of CV weighted graph
states.Comment: 5 pages, 6 figure
The Conformal Window of deformed CFT's in the planar limit
We discuss in the planar approximation the effect of double-trace
deformations on CFT's. We show that this large class of models posses a
conformal window describing a non-trivial flow between two fixed points of the
renormalization group, and reveal the presence of a resonance which we
associate to the remnant of a dilaton pole. As the conformal window shrinks to
zero measure the theory undergoes a conformal phase transition separating a
symmetric from a nonsymmetric phase. The recently conjectured strongly coupled
branch of non-supersymmetric, non-abelian gauge theories with a large number of
flavors is analyzed in light of these results, and a model for the strong
branch is proposed. Some phenomenological implications in the context of
unparticle physics are also emphasized.Comment: 15 pages PRD class, 2 figures, to be published in PR
Supersonic quantum communication
When locally exciting a quantum lattice model, the excitation will propagate
through the lattice. The effect is responsible for a wealth of non-equilibrium
phenomena, and has been exploited to transmit quantum information through spin
chains. It is a commonly expressed belief that for local Hamiltonians, any such
propagation happens at a finite "speed of sound". Indeed, the Lieb-Robinson
theorem states that in spin models, all effects caused by a perturbation are
limited to a causal cone defined by a constant speed, up to exponentially small
corrections. In this work we show that for translationally invariant bosonic
models with nearest-neighbor interactions, this belief is incorrect: We prove
that one can encounter excitations which accelerate under the natural dynamics
of the lattice and allow for reliable transmission of information faster than
any finite speed of sound. The effect is only limited by the model's range of
validity (eventually by relativity). It also implies that in non-equilibrium
dynamics of strongly correlated bosonic models far-away regions may become
quickly entangled, suggesting that their simulation may be much harder than
that of spin chains even in the low energy sector.Comment: 4+3 pages, 1 figure, some material added, typographic error fixe
Evaluation of the Free Energy of Two-Dimensional Yang-Mills Theory
The free energy in the weak-coupling phase of two-dimensional Yang-Mills
theory on a sphere for SO(N) and Sp(N) is evaluated in the 1/N expansion using
the techniques of Gross and Matytsin. Many features of Yang-Mills theory are
universal among different gauge groups in the large N limit, but significant
differences arise in subleading order in 1/N.Comment: 10 pages; no figures; LaTe
Experimental and Theoretical Search for a Phase Transition in Nuclear Fragmentation
Phase transitions of small isolated systems are signaled by the shape of the
caloric equation of state e^*(T), the relationship between the excitation
energy per nucleon e^* and temperature. In this work we compare the
experimentally deduced e^*(T) to the theoretical predictions. The
experimentally accessible temperature was extracted from evaporation spectra
from incomplete fusion reactions leading to residue nuclei. The experimental
e^*(T) dependence exhibits the characteristic S-shape at e^* = 2-3 MeV/A. Such
behavior is expected for a finite system at a phase transition. The observed
dependence agrees with predictions of the MMMC-model, which simulates the total
accessible phase-space of fragmentation
The stability of the spectator, Dirac, and Salpeter equations for mesons
Mesons are made of quark-antiquark pairs held together by the strong force.
The one channel spectator, Dirac, and Salpeter equations can each be used to
model this pairing. We look at cases where the relativistic kernel of these
equations corresponds to a time-like vector exchange, a scalar exchange, or a
linear combination of the two. Since the model used in this paper describes
mesons which cannot decay physically, the equations must describe stable
states. We find that this requirement is not always satisfied, and give a
complete discussion of the conditions under which the various equations give
unphysical, unstable solutions
Ambiguities in statistical calculations of nuclear fragmentation
The concept of freeze out volume used in many statistical approaches for
disassembly of hot nuclei leads to ambiguities. The fragmentation pattern and
the momentum distribution (temperature) of the emanated fragments are
determined by the phase space at the freeze-out volume where the interaction
among the fragments is supposedly frozen out. However, to get coherence with
the experimental momentum distribution of the charged particles, one introduces
Coulomb acceleration beyond this freeze-out. To be consistent, we investigate
the effect of the attractive nuclear force beyond this volume and find that the
possible recombination of the fragments alters the physical observables
significantly casting doubt on the consistency of the statistical model.Comment: 11 pages+3 figure
An Exact Prediction of N=4 SUSYM Theory for String Theory
We propose that the expectation value of a circular BPS-Wilson loop in N=4
SUSYM can be calculated exactly, to all orders in a 1/N expansion and to all
orders in g^2 N. Using the AdS/CFT duality, this result yields a prediction of
the value of the string amplitude with a circular boundary to all orders in
alpha' and to all orders in g_s. We then compare this result with string
theory. We find that the gauge theory calculation, for large g^2 N and to all
orders in the 1/N^2 expansion does agree with the leading string theory
calculation, to all orders in g_s and to lowest order in alpha'. We also find a
relation between the expectation value of any closed smooth Wilson loop and the
loop related to it by an inversion that takes a point along the loop to
infinity, and compare this result, again successfully, with string theory.Comment: LaTeX, 22 pages, 3 figures. Argument corrected and two new sections
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