31,760 research outputs found
Colour strings vs. hard pomeron in perturbative QCD
Average multiplicities and transverse momenta in AA collisions are studied in
the soft and hard regions, in fusing string and perturbative QCD scenarios
respectively. Striking similarities are found between the predictions of the
two approaches. Multiplicities per string and average p_t^2 are found to,
respectively, drop and rise with A in a very similar manner, so that their
product is nearly a constant. In both approaches total multiplicities grow as
A, that is as the number of participants. The high tail of the p_t distribution
is found to behave as A^1.1 in the perturbative QCD scenario.Comment: 10 pages, 8 figure
- dependence of the flow coefficients for pp collisions in the color string scenario. Monte-Carlo simulations
In the color string picture with fusion and percolation the dependence of the
flow coefficients on the transverse momentum is studied for pp collisions
the LHC energy respectively. Monte-Carlo simulations are used to locate simple
strings and their fused clusters. The results favorably agree with the CMS data
in the region GeV/c appropriate for the string scenario.Comment: 10 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1407.459
Fusion of strings vs. percolation and the transition to the quark-gluon plasma
In most of the models of hadronic collisions the number of exchanged colour
strings grows with energy and atomic numbers of the projectile and target. At
high string densities interaction between them should melt them into the
quark-gluon plasma state. It is shown that under certain assumptions about the
the string interaction, a phase transition to the quark gluon plasma indeed
takes place in the system of many colour strings. It may be of the first or
second order (percolation), depending on the particular mechanism of the
interaction. The critical string density is about unity in both cases. The
critical density may have been already reached in central Pb-Pb collisions at
158 A GeV.Comment: 16 pages, 3 Postscript figure
coupling constant in light cone QCD sum rules
We employ the light cone QCD sum rules to calculate coupling
constant by studying the two point correlation function between the vacuum and
the pion state. Our result is consistent with the traditional QCD sum rules
calculations and it is in agreement with the experimental value.Comment: 8 pages, latex, 2 figure
Helioseismic holography of simulated sunspots: magnetic and thermal contributions to travel times
Wave propagation through sunspots involves conversion between waves of
acoustic and magnetic character. In addition, the thermal structure of sunspots
is very different than that of the quiet Sun. As a consequence, the
interpretation of local helioseismic measurements of sunspots has long been a
challenge. With the aim of understanding these measurements, we carry out
numerical simulations of wave propagation through sunspots. Helioseismic
holography measurements made from the resulting simulated wavefields show
qualitative agreement with observations of real sunspots. We use additional
numerical experiments to determine, separately, the influence of the thermal
structure of the sunspot and the direct effect of the sunspot magnetic field.
We use the ray approximation to show that the travel-time shifts in the thermal
(non-magnetic) sunspot model are primarily produced by changes in the wave path
due to the Wilson depression rather than variations in the wave speed. This
shows that inversions for the subsurface structure of sunspots must account for
local changes in the density. In some ranges of horizontal phase speed and
frequency there is agreement (within the noise level in the simulations)
between the travel times measured in the full magnetic sunspot model and the
thermal model. If this conclusion proves to be robust for a wide range of
models, it would suggest a path towards inversions for sunspot structure.Comment: Accepted for publication in The Astrophysical Journa
Sample-to-sample fluctuations and bond chaos in the -component spin glass
We calculate the finite size scaling of the sample-to-sample fluctuations of
the free energy of the component vector spin glass in the
large- limit. This is accomplished using a variant of the interpolating
Hamiltonian technique which is used to establish a connection between the free
energy fluctuations and bond chaos. The calculation of bond chaos then shows
that the scaling of the free energy fluctuaions with system size is with , and very likely
exactly.Comment: 12 pages, 1 figur
Prospects for the Detection of the Deep Solar Meridional Circulation
We perform helioseismic holography to assess the noise in p-mode travel-time
shifts which would form the basis of inferences of large-scale flows throughout
the solar convection zone. We also derive the expected travel times from a
parameterized return (equatorward) flow component of the meridional circulation
at the base of the convection zone from forward models under the assumption of
the ray and Born approximations. From estimates of the signal-to-noise ratio
for measurements focused near the base of the convection zone, we conclude that
the helioseismic detection of the deep meridional flow including the return
component may not be possible using data spanning an interval less than a solar
cycle
On the relation between Differential Privacy and Quantitative Information Flow
Differential privacy is a notion that has emerged in the community of
statistical databases, as a response to the problem of protecting the privacy
of the database's participants when performing statistical queries. The idea is
that a randomized query satisfies differential privacy if the likelihood of
obtaining a certain answer for a database is not too different from the
likelihood of obtaining the same answer on adjacent databases, i.e. databases
which differ from for only one individual. Information flow is an area of
Security concerned with the problem of controlling the leakage of confidential
information in programs and protocols. Nowadays, one of the most established
approaches to quantify and to reason about leakage is based on the R\'enyi min
entropy version of information theory. In this paper, we analyze critically the
notion of differential privacy in light of the conceptual framework provided by
the R\'enyi min information theory. We show that there is a close relation
between differential privacy and leakage, due to the graph symmetries induced
by the adjacency relation. Furthermore, we consider the utility of the
randomized answer, which measures its expected degree of accuracy. We focus on
certain kinds of utility functions called "binary", which have a close
correspondence with the R\'enyi min mutual information. Again, it turns out
that there can be a tight correspondence between differential privacy and
utility, depending on the symmetries induced by the adjacency relation and by
the query. Depending on these symmetries we can also build an optimal-utility
randomization mechanism while preserving the required level of differential
privacy. Our main contribution is a study of the kind of structures that can be
induced by the adjacency relation and the query, and how to use them to derive
bounds on the leakage and achieve the optimal utility
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