Acta Physica

Fast Scramblers and Non-commutative Gauge Theories. (arXiv:1204.5748v1 [hep-th])

Fri, 27 Apr 2012 19:29:36 +0000

Fast scramblers are quantum systems which thermalize in a time scale
logarithmic in the number of degrees of freedom of the system. Non-locality has
been argued to be an essential feature of fast scramblers. We provide evidence
in support of the crucial role of non-locality in such systems by considering
the approach to thermalization in a (strongly-coupled) high temperature
non-commutative gauge theory. We show that non-locality inherent to
non-commutative gauge theories does indeed accelerate the rate of dissipation
in the heat bath in stark contrast to the slow random walk diffusive behavior
prevalent in local field theories.

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Turkey earthquake reveals a new active fault zone

Mon, 24 Oct 2011 14:08:40 +0000

Recent earthquakes in Turkey have occurred along one or other of the country’s two main faults. Yesterday’s quake struck near their meeting point

New Scientist – Physics & Math… Continue reading ...

Shear modulus of the hadron-quark mixed phase. (arXiv:1110.4650v1 [astro-ph.SR])

Mon, 24 Oct 2011 12:59:43 +0000

Robust arguments predict that a hadron-quark mixed phase may exist in the
cores of some “neutron” stars. Such a phase forms a crystalline lattice with a
shear modulus higher than that of the crust due to the high density and charge
separation, even allowing for the effects of charge screening. This may lead to
strong continuous gravitational-wave emission from rapidly rotating neutron
stars and gravitational-wave bursts associated with magnetar flares and pulsar
glitches. We present the first detailed calculation of the shear modulus of the
mixed phase. We describe the quark phase using the bag model plus first-order
quantum chromodynamics corrections and the hadronic phase using relativistic
mean-field models with parameters allowed by the most massive pulsar. Most of
the calculation involves treating the “pasta phases” of the lattice via
dimensional continuation, and we give a general method for computing
dimensionally continued lattice sums including the Debye model of charge
screening. We compute all the shear components of the elastic modulus tensor
and angle average them to obtain the effective (scalar) shear modulus for the
case where the mixed phase is a polycrystal. We include the contributions from
changing the cell size, which are necessary for the stability of the
lower-dimensional portions of the lattice. Stability also requires a minimum
surface tension, generally tens of MeV/fm^2 depending on the equation of state.
We find that the shear modulus can be a few times 10^33 erg/cm^3, two orders of
magnitude higher than the first estimate, over a significant fraction of the
maximum mass stable star for certain parameter choices.

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Origin and meaning of quantum nonlocality. (arXiv:1110.4641v1 [quant-ph])

Mon, 24 Oct 2011 11:06:44 +0000

Quantum nonlocality is revisited from a novel point of view by studying the
problem of an originally classical particle immersed in the stochastic
zero-point radiation field (zpf). The entire system is left to evolve until it
reaches a state in which the radiative terms cancel each other in the mean in a
first approximation. The ensuing approximate statistical description reduced to
the particle’s configuration space contains a nonclassical term due to the
dispersion of the momentum, which depends on the density of particles {\rho}(x)
and thus is nonlocal. This description is shown to be equivalent to
Schr\”odinger’s equation and its complex conjugate. The nonlocal term is
recognized as the so-called quantum potential, thus solving the long standing
problem of the origin and meaning of this term. Further, the relationship
between the Wigner function and a true Kolmogorovian probability density in
phase space is discussed from the perspective provided by this theory.

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SLAC software developer discusses physics simulation tool to make cancer therapy safer

Mon, 24 Oct 2011 07:10:03 +0000

Tiny particles are making a big difference in the world of cancer therapy. And SLAC physicists—experts in particle transport—are using computer simulations to make those therapies safer.
PHYSorg.com: Physics News

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Quantum Mechanics, Spacetime Locality, and Gravity. (arXiv:1110.4630v1 [hep-th])

Mon, 24 Oct 2011 02:06:34 +0000

Quantum mechanics introduces the concept of probability at the fundamental
level, yielding the measurement problem. On the other hand, recent progress in
cosmology has led to the “multiverse” picture, in which our observed universe
is only one of the many, bringing an apparent arbitrariness in defining
probabilities, called the measure problem.

In this paper, we discuss how these two problems are intimately related with
each other, developing a complete picture for quantum measurement and
cosmological histories in the quantum mechanical universe. On one hand, quantum
mechanics eliminates the arbitrariness of defining probabilities in the
multiverse, as discussed in arXiv:1104.2324. On the other hand, the multiverse
allows for understanding why we observe an ordered world obeying consistent
laws of physics, by providing an infinite-dimensional Hilbert space. This
results in the irreversibility of quantum measurement, despite the fact that
the evolution of the multiverse state is unitary.

In order to describe the cosmological dynamics correctly, we need to identify
the structure of the Hilbert space for a system with gravity. We argue that in
order to keep spacetime locality, the Hilbert space for dynamical spacetime
must be defined only in restricted spacetime regions: in and on the (stretched)
apparent horizon as viewed from a fixed reference frame. This requirement
arises from eliminating all the redundancies and overcountings in a general
relativistic, global spacetime description of nature. It is responsible for
horizon complementarity as well as the “observer dependence” of
horizons/spacetime—these phenomena arise to represent changes of the
reference frame in the relevant Hilbert space. This can be viewed as an
extension of the Poincare transformation in the quantum gravitational context,
as the Lorentz transformation is viewed as an extension of the Galilean
transformation.

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rapidshare covariant derivative

Vote Now! Top Space Stories of the Week – Oct. 23, 2011

Mon, 24 Oct 2011 00:08:53 +0000

Was it the doomed falling satellite, the possibilities of vacations to space or something else?

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The Dark Matter & Dark Energy [1/5]

Sun, 23 Oct 2011 17:15:58 +0000

Dark matter are invisible objects that react with matter by gravitational force. Scientists believe that the dark matter is made up of exotic particles like WIMPs(Weakly Interacting Massive Particles).In physical cosmology, dark energy is an exotic form of energy that permeates all of space and tends to increase the rate of expansion of the universe.Dark energy is the most popular way to explain recent observations that the universe appears to be expanding at an accelerating rate. In the standard model of cosmology, dark energy currently accounts for 73% of the total mass-energy of the universe.

History Channel The Universe Dark Matter

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Vehicle Preps, Inspections, Plumbing and Science for Station Crew

Sun, 23 Oct 2011 17:09:10 +0000

The Expedition 29 crew wrapped up its work week conducting inspection and plumbing work. They performed ongoing science and readied a supply ship for undocking. Meanwhile in Russia, the ISS Progress 45 resupply craft is being prepared for launch with docking planned for Nov. 2.

Commander Mike Fossum spent time on the Binary Colloidal Alloy Test experiment which observes microscopic particles, or colloids, suspended in a liquid. He photographed samples from the experiment that could lead to i [...]

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Dark Matter after BESS-Polar II. (arXiv:1110.4376v1 [hep-ph])

Sun, 23 Oct 2011 17:06:31 +0000

The BESS-Polar collaboration has recently performed a precise measurement of
the local antiproton flux which is consistent with a pure secondary production
of antiprotons. We constrain a possible primary component originating from dark
matter pair-annihilations. We derive limits on the annihilation cross section
which are stronger than or comparable to those from the PAMELA satellite
experiment for dark matter masses up to 200 GeV. Especially, we exclude thermal
WIMPs with masses in the range 3-20 GeV if they annihilate dominantly into
quark pairs unless their cross section is velocity suppressed.

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