68,197 research outputs found
Charmonium moving through a strongly coupled QCD plasma: a holographic perspective
We study the properties of charmonium in a strongly coupled QCD-like plasma
at finite momentum. As a basis for this study, a "bottom-up" holographic model
is used which has been previously shown to reproduce charmonium phenomenology
in vacuum and give a reasonable dissociation temperature at zero momentum. The
finite momentum spectral functions are presented and found to be consistent
with recent lattice results. The in-medium dispersion relation and momentum
dependence of decay width of J/Psi have also been studied. We find no signature
of a subluminal limiting velocity from the dispersion relation, while we note
that the dissociation temperature decreases with momentum faster than previous
holographic models. Based upon the dissociation temperature, a maximum momentum
for J/Psi in medium is identified and its phenomenological implications on
J/Psi suppression are discussed.Comment: 23 pages, 8 figures. References added. Published versio
The Inverse Spectral Transform for the Dunajski hierarchy and some of its reductions, I: Cauchy problem and longtime behavior of solutions
In this paper we apply the formal Inverse Spectral Transform for integrable
dispersionless PDEs arising from the commutation condition of pairs of
one-parameter families of vector fields, recently developed by S. V. Manakov
and one of the authors, to one distinguished class of equations, the so-called
Dunajski hierarchy. We concentrate, for concreteness, i) on the system of PDEs
characterizing a general anti-self-dual conformal structure in neutral
signature, ii) on its first commuting flow, and iii) on some of their basic and
novel reductions. We formally solve their Cauchy problem and we use it to
construct the longtime behavior of solutions, showing, in particular, that
unlike the case of soliton PDEs, different dispersionless PDEs belonging to the
same hierarchy of commuting flows evolve in time in very different ways,
exhibiting either a smooth dynamics or a gradient catastrophe at finite time
Dynamical Response of Fermi Condensate to Varying Magnetic Fields
We investigate the dynamical response of strongly interacting ultra-cold
fermionic atoms near Feshbach resonance to varying magnetic fields. Following
the experimental practices, we calculate the response of the atoms to
oscillating and to linearly ramped magnetic fields respectively. For
oscillating magnetic fields, depending on the frequencies and the amplitudes of
the oscillations, the response of the pair excitation gap shows either linear
or rich non-linear behaviour. In addition, both the spectral studies through
the linear response theory and the time-domain simulations suggest the
existence of a resonant frequency corresponding to the pair dissociation
threshold. For linearly ramped magnetic fields, the response of the excitation
gap shows damped oscillations. The final value of the excitation gap depends on
the rate of the field sweep.Comment: 6 pages, 6 figure
K-essence Explains a Lorentz Violation Experiment
Recently, a state of the art experiment shows evidence for Lorentz violation
in the gravitational sector. To explain this experiment, we investigate a
spontaneous Lorentz violation scenario with a generalized scalar field. We find
that when the scalar field is nonminimally coupled to gravity, the Lorentz
violation induces a deformation in the Newtonian potential along the direction
of Lorentz violation.Comment: 8 pages, the final version, discussion and references adde
Comment on "Critical and slow dynamics in a bulk metallic glass exhibiting strong random magnetic anisotropy" [Appl. Phys. Lett. 92, 011923 (2008)]
In this comment, by using Monte Carlo simulation, we show that the
perpendicular shift of hysteresis loops reported in the commented work is
nothing special but simply due to the fact that the range of field does not
surpass the reversible field beyond which the two branches of the loop merge.
If the reversible field is exceeded, the shift is no longer observed. Moreover,
we point out that even using a small range of field, the shift will not be
observed if the observation time is long enough for the reversible field to
drop within the range.Comment: 2 pages, 2 figures, accepted for publication in Applied Physics
Letters Volume 94, Issue 15, Issue date 13 April 200
A pure-carbon ring transistor: The role of topology and structure
We report results on the rectification properties of a carbon nanotube (CNT)
ring transistor, contacted by CNT leads, whose novel features have been
recently communicated by Watanabe et al. [Appl. Phys. Lett. 78, 2928 (2001)].
This paper contains results which are validated by the experimental
observations. Moreover, we report on additional features of the transmission of
this ring device which are associated with the possibility of breaking the lead
inversion symmetry. The linear conductance displays a "chessboard"-like
behavior alternated with anomalous zero-lines which should be directly
observable in experiments. We are also able to discriminate in our results
structural properties (quasi-onedimensional confinement) from pure topological
effects (ring configuration), thus helping to gain physical intuition on the
rich ring phenomenology.Comment: 3 pages, 4 figure
An ac field probe for the magnetic ordering of magnets with random anisotropy
A Monte Carlo simulation is carried out to investigate the magnetic ordering
in magnets with random anisotropy (RA). Our results show peculiar similarities
to recent experiments that the real part of ac susceptibility presents two
peaks for weak RA and only one for strong RA regardless of glassy critical
dynamics manifested for them. We demonstrate that the thermodynamic nature of
the low-temperature peak is a ferromagnetic-like dynamic phase transition to
quasi-long range order (QLRO) for the former. Our simulation, therefore, is
able to be incorporated with the experiments to help clarify the existence of
the QLRO theoretically predicted so far.Comment: 10 pages, 4 figures, to appear in Appl. Phys. Lett. volume 95, Issue
22, Isue date: 30 November 200
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