155 research outputs found
Structural transitions and nonmonotonic relaxation processes in liquid metals
Structural transitions in melts as well as their dynamics are considered. It
is supposed that liquid represents the solution of relatively stable solid-like
locally favored structures (LFS) in the surrounding of disordered normal-liquid
structures. Within the framework of this approach the step changes of liquid Co
viscosity are considered as liquid-liquid transitions. It is supposed that this
sort of transitions represents the cooperative medium-range bond ordering, and
corresponds to the transition of the "Newtonian fluid" to the "structured
fluid". It is shown that relaxation processes with oscillating-like time
behavior (~) of viscosity are possibly close to
this point
Critical Temperature of the Deconfining Phase Transition in (2+1)d Georgi-Glashow Model
We find the temperature of the phase transition in the (2+1)d Georgi-Glashow
model. The critical temperature is shown to depend on the gauge coupling and on
the ratio of Higgs and gauge boson masses. In the BPS limit of light Higgs the
previous result by Dunne, Kogan, Kovner, and Tekin is reproduced.Comment: 17 pages, 3 figures, REVTeX
The Hydrodynamics of M-Theory
We consider the low energy limit of a stack of N M-branes at finite
temperature. In this limit, the M-branes are well described, via the AdS/CFT
correspondence, in terms of classical solutions to the eleven dimensional
supergravity equations of motion. We calculate Minkowski space two-point
functions on these M-branes in the long-distance, low-frequency limit, i.e. the
hydrodynamic limit, using the prescription of Son and Starinets
[hep-th/0205051]. From these Green's functions for the R-currents and for
components of the stress-energy tensor, we extract two kinds of diffusion
constant and a viscosity. The N dependence of these physical quantities may
help lead to a better understanding of M-branes.Comment: 1+19 pages, references added, section 5 clarified, eq. (72) correcte
Reheating and thermalization in a simple scalar model
We consider a simple model for the Universe reheating, which consists of a
single self--interacting scalar field in Minkowskian space--time. Making use of
the existence of an additional small parameter proportional to the amplitude of
the initial spatially homogeneous field oscillations, we show that the behavior
of the field can be found reliably. We describe the evolution of the system
from the homogeneous oscillations to the moment when thermalization is
completed. We compare our results with the Hartree--Fock approximation and
argue that some properties found for this model may be the common features of
realistic theories.Comment: Some changes in Introduction and Discussion, comparison with the
Hartree--Fock results added. 37 pages, 2 postscript figures attache
Sound Waves in (2+1) Dimensional Holographic Magnetic Fluids
We use the AdS/CFT correspondence to study propagation of sound waves in
strongly coupled (2+1) dimensional conformal magnetic fluids. Our computation
provides a nontrivial consistency check of the viscous magneto-hydrodynamics of
Hartnoll-Kovtun-Muller-Sachdev to leading order in the external field.
Depending on the behavior of the magnetic field in the hydrodynamic limit, we
show that it can lead to further attenuation of sound waves in the (2+1)
dimensional conformal plasma, or reduce the speed of sound. We present both
field theory and dual supergravity descriptions of these phenomena. While to
the leading order in momenta the dispersion of the sound waves obtained from
the dual supergravity description agrees with the one predicted from field
theory, we find a discrepancy at higher order. This suggests that further
corrections to HKMS magneto-hydrodynamics are necessary.Comment: 32 pages, LaTeX; minor corrections, references added; an error in the
boundary conditions fixed, a slight change in the result
Null energy condition and superluminal propagation
We study whether a violation of the null energy condition necessarily implies
the presence of instabilities. We prove that this is the case in a large class
of situations, including isotropic solids and fluids relevant for cosmology. On
the other hand we present several counter-examples of consistent effective
field theories possessing a stable background where the null energy condition
is violated. Two necessary features of these counter-examples are the lack of
isotropy of the background and the presence of superluminal modes. We argue
that many of the properties of massive gravity can be understood by associating
it to a solid at the edge of violating the null energy condition. We briefly
analyze the difficulties of mimicking in scalar tensor theories of
gravity.Comment: 46 pages, 6 figure
Homogeneous Fermion Superfluid with Unequal Spin Populations
For decades, the conventional view is that an s-wave BCS superfluid can not
support uniform spin polarization due to a gap in the quasiparticle
excitation spectrum. We show that this is an artifact of the dismissal of
quasiparticle interactions in the conventional approach at the
outset. Such interactions can cause triplet fluctuations in the ground state
and hence non-zero spin polarization at "magnetic field" . The
resulting ground state is a pairing state of quasiparticles on the ``BCS
vacuum". For sufficiently large , the spin polarization of at unitarity
has the simple form . Our study is motivated by the recent
experiments at Rice which found evidence of a homogenous superfluid state with
uniform spin polarization.Comment: 4 pages, 3 figure
The Second Sound of SU(2)
Using the AdS/CFT correspondence, we calculate the transport coefficients of
a strongly interacting system with a non-abelian SU(2) global symmetry near a
second order phase transition. From the behavior of the poles in the Green's
functions near the phase transition, we determine analytically the speed of
second sound, the conductivity, and diffusion constants. We discuss
similarities and differences between this and other systems with vector order
parameters such as p-wave superconductors and liquid helium-3.Comment: 31 pages, 2 figures; v2 ref added, typo fixe
Gauged Lifshitz scalar field theories in two dimensions
We present two-dimensional gauged Lifshitz scalar field theories by
considering the duality relation between the source current and the Noether
current. Requiring the duality partially, we obtain a gauged model which
recovers the bosonized Schwinger model for the IR limit. For the exact duality,
however, the source current is not conserved, which means that the resulting
theory is anomalous, so that the number of degrees of freedom is increased. The
second model is consistently formulated by adding the Wess-Zumino type action
to maintain the gauge invariance.Comment: 11 page
Fluid dynamics of R-charged black holes
We construct electrically charged AdS_5 black hole solutions whose charge,
mass and boost-parameters vary slowly with the space-time coordinates. From the
perspective of the dual theory, these are equivalent to hydrodynamic
configurations with varying chemical potential, temperature and velocity
fields. We compute the boundary theory transport coefficients associated with a
derivative expansion of the energy momentum tensor and R-charge current up to
second order. In particular, we find a first order transport coefficient
associated with the axial component of the current.Comment: 31 pages, v2: published version; added some references, discussion of
the charge-current changed, results unchanged, v3: typo in formula (15)
changed, v4: added footnote 3 in order to clarify the relation of our results
to those of arXiv:0809.259
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