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

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

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

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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Heavy Quark Dynamics in the QGP. (arXiv:1110.4138v1 [hep-ph])

We assess transport properties of heavy quarks in the Quark-Gluon Plasma
(QGP) that show a strong non-perturbative behavior. A T-matrix approach based
on a potential taken from lattice QCD hints at the presence of heavy-quark (HQ)
resonant scattering with an increasing strength as the temperature, $ T$ ,
reaches the critical temperature, $ T_c \simeq 170 \; \MeV$ for deconfinement
from above. The implementation of HQ resonance scattering along with a
hadronization via quark coalescence under the conditions of the plasma created
in heavy-ion collisions has been shown to correctly describe both the nuclear
modification factor, $ R_{AA}$ , and the elliptic flow, $ v_2$ , of single
electrons at RHIC and have correctly predicted the $ R_{AA}$ of D mesons at LHC
energy.

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Stability of nodal structures in graph eigenfunctions and its relation to the nodal domain count. (arXiv:1110.3802v1 [math-ph])

The nodal domains of eigenvectors of the discrete Schrodinger operator on
simple, finite and connected graphs are considered. Courant’s well known nodal
domain theorem applies in the present case, and sets an upper bound to the
number of nodal domains of eigenvectors: Arranging the spectrum as a non
decreasing sequence, and denoting by $ \nu_n$ the number of nodal domains of the
$ n$ ‘th eigenvector, Courant’s theorem guarantees that the nodal deficiency
$ n-\nu_n$ is non negative. (The above applies for generic eigenvectors. Special
care should be exercised for eigenvectors with vanishing components.) The main
result of the present work is that the nodal deficiency for generic
eigenvectors equals to a Morse index of an energy functional whose value at its
relevant critical points coincides with the eigenvalue. The association of the
nodal deficiency to the stability of an energy functional at its critical
points was recently discussed in the context of quantum graphs
[arXiv:1103.1423] and Dirichlet Laplacian in bounded domains in $ R^d$
[arXiv:1107.3489]. The present work adapts this result to the discrete case.
The definition of the energy functional in the discrete case requires a special
setting, substantially different from the one used in
[arXiv:1103.1423,arXiv:1107.3489] and it is presented here in detail.

math-ph updates on arXiv.org

Incoming search terms:

• courant nodal deficiency
• Graph Laplacians and Nodal Domains

… Continue reading …

Studying Deeply Virtual Compton Scattering with Neural Networks. (arXiv:1110.3798v1 [physics.data-an])

Neural networks are utilized to fit Compton form factor H to HERMES data on
deeply virtual Compton scattering off unpolarized protons. We used this result
to predict the beam charge-spin assymetry for muon scattering off proton at the
kinematics of the COMPASS II experiment.

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The magnetic mass of transverse gluon, the B-meson weak decay vertex and the triality symmetry of octonion. (arXiv:1110.3857v1 [hep-ph])

With an assumption that in the Yang-Mills Lagrangian, a left-handed fermion
and a right-handed fermion both expressed as quaternion make an octonion which
possesses the triality symmetry, I calculate the magnetic mass of the
transverse self-dual gluon from three loop diagram, in which a heavy quark pair
is created and two self-dual gluons are interchanged.

The magnetic mass of the transverse gluon depends on the mass of the pair
created quarks, and in the case of charmed quark pair creation, the magnetic
mass $ m_{mag}$ becomes approximately equal to $ T_c$ at $ T=T_c\sim
1.14\Lambda_{\bar{MS}}\sim 260$ MeV. Corrections in the B-meson weak decay
vertex from the two self-dual gluon exchange is also evaluated.

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Gauge Field Production in Axion Inflation: Consequences for Monodromy, non-Gaussianity in the CMB, and Gravitational Waves at Interferometers. (arXiv:1110.3327v1 [astro-ph.CO])

Models of inflation based on axions, which owe their popularity to the
robustness against UV corrections, have also a very distinct class of
signatures. The relevant interactions of the axion are a non-perturbative
oscillating contribution to the potential and a shift-symmetric coupling to
gauge fields. We review how these couplings affect the cosmological
perturbations via a unified study based on the in-in formalism. We then note
that, when the inflaton coupling to gauge fields is high enough to lead to
interesting observational results, the backreaction of the produced gauge
quanta on the inflaton dynamics becomes relevant during the final stage of
inflation, and prolongs its duration by about 10 e-foldings. We extend existing
results on gravity wave production in these models to account for this late
inflationary phase. The strong backreaction phase results in an enhancement of
the gravity wave signal at the interferometer scales. As a consequence, the
signal is potentially observable at Advanced LIGO/VIRGO for the most natural
duration of inflation in such models. Finally, we explicitly compute the axion
couplings to gauge fields in string theory construction of axion monodromy
inflation and identify cases where they can trigger interesting
phenomenological effects.

hep-th updates on arXiv.org

Incoming search terms:

• bizon rostworowski instability anti de sitter

… Continue reading …

Hadron production in pA collisions at the LHC from the Color Glass Condensate. (arXiv:1110.2810v1 [hep-ph])

We investigate the contribution of inelastic and elastic processes to single
inclusive hadron production in proton-proton and proton (deuteron)-nucleus
collisions at RHIC and the LHC. Using the hybrid formulation which includes
both elastic and inelastic contributions, supplemented with the
running-coupling Balitsky-Kovchegov equation, we get a good description of RHIC
data. It is shown that inclusion of the inelastic terms makes the transverse
momentum dependence of the production cross section steeper in the mid-rapidity
region but does not affect the cross section in the very forward region. The
inelastic processes also lead to a sharper increase of the nuclear modification
factor R_{pA} with increasing p_T. We also make predictions for the nuclear
modification factor in proton-nucleus collisions at the LHC (\sqrt{s}=4.4 and
8.8 TeV) at forward rapidities using the Color-Glass-Condensate framework.

hep-ex updates on arXiv.org… Continue reading …

Hawking radiation for a Proca field in D-dimensions. (arXiv:1110.2485v1 [gr-qc])

We study the wave equation of a massive vector boson in the background of a
D-dimensional Schwarzschild black hole. The mass term introduces a coupling
between two physical degrees of freedom of the field, and we solve the
resulting system of ODEs numerically, without decoupling. We show how to define
decoupled transmission factors from an S-matrix and compute them for various
modes, masses and space-time dimensions. The mass term lifts the degeneracy
between transverse modes, in D=4, and excites the longitudinal modes, in
particular the s-wave. Moreover, it increases the contribution of waves with
larger angular momentum, which can be dominant at intermediate energies. The
transmission factors are then used to obtain the Hawking fluxes in this
channel. Our results alert for the importance of modelling the longitudinal
modes correctly, instead of treating them as decoupled scalars as in current
black hole event generators; thus they can be used to improve such generators
for phenomenological studies of TeV gravity scenarios.

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