Heavy Quark Dynamics in the QGP. (arXiv:1110.4138v1 [hep-ph])
October 20, 2011 by Actaphysica
Filed under High-Energy Physics
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.
hep-ph updates on arXiv.org… Continue reading …
Stability of nodal structures in graph eigenfunctions and its relation to the nodal domain count. (arXiv:1110.3802v1 [math-ph])
October 19, 2011 by Actaphysica
Filed under High-Energy Physics
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.
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Studying Deeply Virtual Compton Scattering with Neural Networks. (arXiv:1110.3798v1 [physics.data-an])
October 19, 2011 by Actaphysica
Filed under High-Energy Physics
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])
October 18, 2011 by Actaphysica
Filed under High-Energy Physics
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.
hep-lat updates on arXiv.org… Continue reading …
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])
October 18, 2011 by Actaphysica
Filed under High-Energy Physics
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.
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Luttinger Liquid Physics and Spin-Flip Scattering on Helical Edges. (arXiv:1110.3322v1 [cond-mat.str-el])
October 18, 2011 by Actaphysica
Filed under Condensed Matter Physics
We investigate electronic correlation effects on edge states of quantum spin
Hall insulators within the Kane-Mele-Hubbard model by means of quantum Monte
Carlo simulations. In accordance with Luttinger liquid theory, we find dominant
transverse spin fluctuations with an interaction dependent power law and the
expected doping dependence. For strong electronic correlations, bulk states
become important, and high-energy spectral features beyond Luttinger liquid
theory emerge. Inelastic spin-flip scattering leads to graphene-like edge state
signatures, and transfers spectral weight from low to high energies causing a
suppression of charge transport.
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Spectra of Harmonium in a magnetic field using an initial value representation of the semiclassical propagator. (arXiv:1110.2900v1 [quant-ph])
October 16, 2011 by Actaphysica
Filed under Quantum Physics
For two Coulombically interacting electrons in a quantum dot with harmonic
confinement and a constant magnetic field, we show that time-dependent
semiclassical calculations using the Herman-Kluk initial value representation
of the propagator lead to eigenvalues of the same accuracy as WKB calculations
with Langer correction. The latter are restricted to integrable systems,
however, whereas the time-dependent initial value approach allows for
applications to high-dimensional, possibly chaotic dynamics and is extendable
to arbitrary shapes of the potential.
quant-ph updates on arXiv.org… Continue reading …
Bubble oscillations and motion under vibration. (arXiv:1110.2777v1 [physics.flu-dyn])
October 16, 2011 by Actaphysica
Filed under General Physics
Bubbles under vibration can behave in unusual ways, e.g., moving downward
against the force of buoyancy. While the bubble downward motion due to the
Bjerknes force is well known at acoustic frequencies close to the bubble
resonant frequency, these experiments demonstrate that these effects can be
observed at relatively low frequencies as well. Experiments were performed in a
thin, quasi-two-dimensional rectangular acrylic box partially filled with
20-cSt PDMS silicone oil with overlying ambient air. The apparatus was
subjected to sinusoidal axial vibration that produced breakup of the gas-liquid
free surface, producing liquid jets into the air, droplets pinching off from
these jets, gas cavities in the liquid from impacts of these droplets, and
bubble transport below the interface. Vibration conditions for the attached
videos are 280 Hz frequency, 15 g acceleration, and 94 micron peak-to-peak
displacement. Behaviors shown in the videos include the following. 1. Free
surface breakup into jets and droplets, and formation of bubbles under the free
surface. 2. Bubbles thus generated moving downward in the cell. 3. Bubbles
attracted to the first bubble deep in the cell and eventually merging to form a
large bubble at the base of the cell. 4. Bubble cluster at the base of the cell
merging to form a larger bubble, which stabilizes at a levitated location below
the free surface and acts to damp out the surface breakup. 5. The levitated
bubble interface and its breakup are similar to the free surface breakup into
jets and droplets, but the jets in the bubble are facing downward. Sandia
National Laboratories is a multi-program laboratory managed and operated by
Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation,
for the U.S. Department of Energy’s National Nuclear Security Administration
under contract DE-AC04-94AL85000.
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Light Loop Echoes and Blinking Black Holes. (arXiv:1110.2789v1 [astro-ph.HE])
October 15, 2011 by Actaphysica
Filed under GR-QC
Radiation emitted near a black hole reaches the observer by multiple paths;
and when this radiation varies in time, the time-delays between the various
paths generate a “blinking” effect in the observed light curve L(t) or its
auto-correlation function xi(T)= <L(t)L(t-T)>. For the particularly important
“face-on” configuration (in which the hole is viewed roughly along its spin
axis, while the emission comes roughly from its equatorial plane — e.g. from
the inner edge of its accretion disk, or from the violent flash of a
nearby/infalling star) we calculate the blinking in detail by computing the
time delay Delta t_{j}(r,a) and magnification mu_{j}(r,a) of the jth path
(j=1,2,3,…), relative to the primary path (j=0), as a function of the
emission radius r and black hole spin 0<a/M<1. The particular geometry and
symmetry of the nearly-face-on configuration enhances and “protects” the
blinking signal, making it more detectable and more independent of certain
astrophysical and observational details. The effect can be surprisingly strong:
e.g. for radiation from the innermost stable circular orbit (“ISCO”) of a black
hole of critical spin (a_{crit}/M = 0.853), the j=1,2,3 fluxes are,
respectively, 27%, 2% and 0.1% of the j=0 flux.
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Resonant multi-photon IR dissociation spectroscopy of a trapped and sympathetically cooled biomolecular ion species. (arXiv:1110.2774v1 [physics.chem-ph])
October 15, 2011 by Actaphysica
Filed under General Physics
In this work we demonstrate vibrational spectroscopy of polyatomic ions that
are trapped and sympathetically cooled by laser-cooled atomic ions. We use the
protonated dipeptide tryptophane-alanine (HTyrAla+) as a model system, cooled
by Barium ions to less than 800mK secular temperature. The spectroscopy is
performed on the fundamental vibrational transition of a local vibrational mode
at 2.74 {\mu}m using a continuous-wave optical parametric oscillator (OPO).
Resonant multi-photon IR dissociation spectroscopy (without the use of a UV
laser) generates charged molecular fragments, which are sympathetically cooled
and trapped, and subsequently released from the trap and counted. We measured
the cross section for R-IRMPD under conditions of low intensity, and found it
to be approximately two orders smaller than the vibrational excitation cross
section. The observed rotational bandwidth of the vibrational transition is
larger than the one expected from the combined effects of 300 K black-body
temperature, conformer-dependent line shifts, and intermolecular vibrational
relaxation broadening (J. Stearns et al., J. Chem. Phys., 127, 154322-7
(2007)). This indicates that as the internal energy of the molecule grows, an
increase of the rotational temperature of the molecular ions well above room
temperature (up to on the order of 1000K), and/or an appreciable shift of the
vibrational transition frequency (approx. 6-8 cm$ ^{-1}$ ) occurs.
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