3,018 research outputs found
Meson Excitation at Finite Chemical Potential
We consider a probe stable meson in the holographic quark-gluon plasma at
zero temperature and chemical potential. Due to the energy injection into the
plasma, the temperature and chemical potential are increased to arbitrary
finite values and the meson is also excited. Excitation time tex is the time at
which the meson falls into the final excited state. We study the effect of
various parameters of theory on the excitation time and observe that for larger
values of final temperature and chemical potential the excitation time
increases. Furthermore, our outcomes show that the more stable mesons are
excited sooner.Comment: 10 pages, 9 figures, references added, appendix added, typos
correcte
Dark polariton-solitons in semiconductor microcavities
We report the existence, symmetry breaking and other instabilities of dark
polariton-solitons in semiconductor microcavities operating in the strong
coupling regime. These half-light half-matter solitons are potential candidates
for applications in all-optical signal processing. Their excitation time and
required pump powers are a few orders of magnitude less than those of their
weakly coupled light-only counterparts.Comment: submitted to PR
Impulse-induced localized nonlinear modes in an electrical lattice
Intrinsic localized modes, also called discrete breathers, can exist under
certain conditions in one-dimensional nonlinear electrical lattices driven by
external harmonic excitations. In this work, we have studied experimentally the
efectiveness of generic periodic excitations of variable waveform at generating
discrete breathers in such lattices. We have found that this generation
phenomenon is optimally controlled by the impulse transmitted by the external
excitation (time integral over two consecutive zerosComment: 5 pages, 8 figure
Electron spin orientation under in-plane optical excitation in GaAs quantum wells
We study the optical orientation of electron spins in GaAs/AlGaAs quantum
wells for excitation in the growth direction and for in-plane excitation. Time-
and polarization-resolved photoluminescence excitation measurements show, for
resonant excitation of the heavy-hole conduction band transition, a negligible
degree of electron spin polarization for in-plane excitation and nearly 100%
for excitation in the growth direction. For resonant excitation of the
light-hole conduction band transition, the excited electron spin polarization
has the same (opposite) direction for in-plane excitation (in the growth
direction) as for excitation into the continuum. The experimental results are
well explained by an accurate multiband theory of excitonic absorption taking
fully into account electron-hole Coulomb correlations and heavy-hole light-hole
coupling.Comment: 10 pages, 4 figures, final versio
Terahertz Photoacoustic Spectroscopy Using an MEMS Cantilever Sensor
In this paper, a microelectromechanical systems cantilever sensor was designed, modeled, and fabricated to measure the photoacoustic (PA) response of gases under very low vacuum conditions. The micromachined devices were fabricated using silicon-on-insulator wafers and then tested in a custom-built, miniature, vacuum chamber during this first-ever demonstration. Terahertz radiation was amplitude modulated to excite the gas under test and perform PA molecular spectroscopy. Experimental data show a predominantly linear response that directly correlates measured cantilever deflection to PA signals. Excellent low pressure (i.e., 2-40 mTorr) methyl cyanide PA spectral data were collected resulting in a system sensitivity of 1.97 Ă— 10 -5 cm -1 and a normalized noise equivalent absorption coefficient of 1.39 Ă— 10 -9 cm -1 W Hz -1/2
Origin theories for the eccentricities of extrasolar planets
Half the known extrasolar planets have orbital eccentricities in excess of
0.3. Such large eccentricities are surprising as it is thought that planets
form in a protoplanetary disk on nearly circular orbits much like the current
states of the solar system planets. Possible explanations for the large
planetary eccentricities include the perturbations that accompany planet-planet
scattering, the tidal interaction between the gas disk and the planets, Kozai's
secular eccentricity cycles, the eccentricity excitation during planetary pair
migration in mean motion resonance, the perturbations by stellar encounters,
stellar-like relaxation that occurs if planets formed through gravitational
instability, and the relative acceleration by the stellar jet system of the
host star with respect to the companion. In this chapter, we comment on the
relevance and characteristics of the various eccentricity origin theories.Comment: 23 pages, 8 figures. Review lecture at the 2006 Aussois Winter School
"Open Problems in Celestial Mechanics". To appear in Lecture Notes in
Physics, Springe
Double Relaxation via AdS/CFT
We exploit the AdS/CFT correspondence to investigate thermalization in an N=2
strongly coupled gauge theory including massless fundamental matter (quark).
More precisely, we consider the response of a zero temperature state of the
gauge theory under variation of an external electric field leading to a
time-dependent current. The holographic dual of the above set-up is given by
introducing a time-dependent electric field on the probe D7-brane embedded in
an AdS_5 X S^5 background. In the dual gravity theory, due to a time-dependent
electric field an apparent horizon forms on the brane which, according to
AdS/CFT dictionary, is the counterpart of the thermalization process in the
gauge theory. We classify different functions for time-dependent electric field
and study their effect on the apparent horizon formation. In the case of pulse
functions where the electric field varies from zero to zero, apart from
non-equilibrium phase, we observe that two apparent horizons form on the brane.
On the gauge theory side, it means that the state of the gauge theory
experiences two different temperatures during the time evolution.Comment: 28 pages, 13 figures, published versio
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