1,858 research outputs found
Exact Calculation of the Vortex-Antivortex Interaction Energy in the Anisotropic 3D XY-model
We have developed an exact method to calculate the vortex-antivortex
interaction energy in the anisotropic 3D-XY model. For this calculation, dual
transformation which is already known for the 2D XY-model was extended. We
found an explicit form of this interaction energy as a function of the
anisotropic ratio and the separation between the vortex and antivortex
located on the same layer. The form of interaction energy is at the
small limi t but is proportional to at the opposite limit. This form of
interaction energ y is consistent with the upper bound calculation using the
variational method by Cataudella and Minnhagen.Comment: REVTeX 12 pages, In print for publication in Phys. Rev.
Observed Effect of Magnetic Fields on the Propagation of Magnetoacoustic Waves in the Lower Solar Atmosphere
We study Hinode/SOT-FG observations of intensity fluctuations in Ca II H-line
and G-band image sequences and their relation to simultaneous and co-spatial
magnetic field measurements. We explore the G-band and H-line intensity
oscillation spectra both separately and comparatively via their relative phase
differences, time delays and cross-coherences. In the non-magnetic situations,
both sets of fluctuations show strong oscillatory power in the 3 - 7 mHz band
centered at 4.5 mHz, but this is suppressed as magnetic field increases. A
relative phase analysis gives a time delay of H-line after G-band of 20\pm1 s
in non-magnetic situations implying a mean effective height difference of 140
km. The maximum coherence is at 4 - 7 mHz. Under strong magnetic influence the
measured delay time shrinks to 11 s with the peak coherence near 4 mHz. A
second coherence maximum appears between 7.5 - 10 mHz. Investigation of the
locations of this doubled-frequency coherence locates it in diffuse rings
outside photospheric magnetic structures. Some possible interpretations of
these results are offered.Comment: 19 pages, 6 figure
Quasi-separatrix layers and three-dimensional reconnection diagnostics for line-tied tearing modes
In three-dimensional magnetic configurations for a plasma in which no closed
field line or magnetic null exists, no magnetic reconnection can occur, by the
strictest definition of reconnection. A finitely long pinch with line-tied
boundary conditions, in which all the magnetic field lines start at one end of
the system and proceed to the opposite end, is an example of such a system.
Nevertheless, for a long system of this type, the physical behavior in
resistive magnetohydrodynamics (MHD) essentially involves reconnection. This
has been explained in terms comparing the geometric and tearing widths [1, 2].
The concept of a quasi-separatrix layer[3, 4] was developed for such systems.
In this paper we study a model for a line-tied system in which the
corresponding periodic system has an unstable tearing mode. We analyze this
system in terms of two magnetic field line diagnostics, the squashing
factor[3-5] and the electrostatic potential difference used in kinematic
reconnection studies[6, 7]. We discuss the physical and geometric significance
of these two diagnostics and compare them in the context of discerning
tearing-like behavior in line-tied modes. [1] G. L. Delzanno and J. M. Finn.
Physics of Plasmas, 15(3):032904, 2008. [2] Y.-M. Huang and E. G. Zweibel.
Physics of Plasmas, 16(4):042102, 2009. [3] E. R. Priest and P. D\'emoulin. J.
Geophys. Res., 100(A12):23443-23463, 1995. [4] P. D\'emoulin, J. C. Henoux, E.
R. Priest, and C. H. Mandrini. Astron. Astrophys., 308:643-655, Apr. 1996. [5]
V. S. Titov and G. Hornig. Advances in Space Research, 29(7):1087-1092, 2002.
[6] Y. Lau and J. M. Finn. The Astrophysical Journal, 350:672-691, Feb. 1990.
[7] Y. Lau and J. M. Finn. The Astrophysical Journal, 366:577-591, 1991.Comment: 13 pages, 9 figures, Submitted to Commun Nonlinear Sci Numer Simula
Random walks and the Hagedorn transition
We study details of the approach to the Hagedorn temperature in string theory
in various static spacetime backgrounds. We show that the partition function
for a {\it single} string at finite temperature is the torus amplitude
restricted to unit winding around Euclidean time. We use the worldsheet path
integral to derive the statement that the the sum over random walks of the
thermal scalar near the Hagedorn transition is precisely the image under a
modular transformation of the sum over spatial configurations of a single
highly excited string. We compute the radius of gyration of thermally excited
strings in . We show that the winding mode indicates an
instability despite the AdS curvature at large radius, and that the negative
mass squared decreases with decreasing AdS radius, much like the type 0
tachyon. We add further arguments to statements by Barbon and Rabinovici, and
by Adams {\it et. al.}, that the Euclidean AdS black hole can thought of as a
condensate of the thermal scalar. We use this to provide circumstantial
evidence that the condensation of the thermal scalar decouples closed string
modes.Comment: 34 pages (7 of references), 5 figures. v2: Reference added, grant
acknowledgement added, typos correcte
Flat space physics from holography
We point out that aspects of quantum mechanics can be derived from the
holographic principle, using only a perturbative limit of classical general
relativity. In flat space, the covariant entropy bound reduces to the
Bekenstein bound. The latter does not contain Newton's constant and cannot
operate via gravitational backreaction. Instead, it is protected by - and in
this sense, predicts - the Heisenberg uncertainty principle.Comment: 11 pages, 3 figures; v2: minor correction
Theory of the first-order isostructural valence phase transitions in mixed valence compounds YbIn_{x}Ag_{1-x}Cu_{4}
For describing the first-order isostructural valence phase transition in
mixed valence compounds we develop a new approach based on the lattice Anderson
model. We take into account the Coulomb interaction between localized f and
conduction band electrons and two mechanisms of electron-lattice coupling. One
is related to the volume dependence of the hybridization. The other is related
to local deformations produced by f- shell size fluctuations accompanying
valence fluctuations. The large f -state degeneracy allows us to use the 1/N
expansion method. Within the model we develop a mean-field theory for the
first-order valence phase transition in YbInCu_{4}. It is shown that the
Coulomb interaction enhances the exchange interaction between f and conduction
band electron spins and is the driving force of the phase transition. A
comparison between the theoretical calculations and experimental measurements
of the valence change, susceptibility, specific heat, entropy, elastic
constants and volume change in YbInCu_{4} and YbAgCu_{4} are presented, and a
good quantitative agreement is found. On the basis of the model we describe the
evolution from the first-order valence phase transition to the continuous
transition into the heavy-fermion ground state in the series of compounds
YbIn_{1-x}Ag_{x}Cu_{4}. The effect of pressure on physical properties of
YbInCu_{4} is studied and the H-T phase diagram is found.Comment: 17 pages RevTeX, 9 Postscript figures, to be submitted to Phys.Rev.
On the Quantum Invariant for the Spherical Seifert Manifold
We study the Witten--Reshetikhin--Turaev SU(2) invariant for the Seifert
manifold where is a finite subgroup of SU(2). We show
that the WRT invariants can be written in terms of the Eichler integral of the
modular forms with half-integral weight, and we give an exact asymptotic
expansion of the invariants by use of the nearly modular property of the
Eichler integral. We further discuss that those modular forms have a direct
connection with the polyhedral group by showing that the invariant polynomials
of modular forms satisfy the polyhedral equations associated to .Comment: 36 page
Field-induced magnetic transitions in the quasi-two-dimensional heavy-fermion antiferromagnets Ce_{n}RhIn_{3n+2} (n=1 or 2)
We have measured the field-dependent heat capacity in the tetragonal
antiferromagnets CeRhIn and CeRhIn, both of which have an
enhanced value of the electronic specific heat coefficient
mJ/mol-Ce K above . For the specific heat data at zero
applied magnetic field are consistent with the existence of an anisotropic
spin-density wave opening a gap in the Fermi surface for CeRhIn while
CeRhIn shows behavior consistent with a simple antiferromagnetic
magnon. From these results, the magnetic structure, in a manner similar to the
crystal structure, appears more two-dimensional in CeRhIn than in
CeRhIn where only about 12% of the Fermi surface remains ungapped
relative to 92% for CeRhIn. When both compounds behave in a
manner expected for heavy fermion systems as both and the electronic
heat capacity decrease as field is applied. When the field is applied in the
tetragonal basal plane (), CeRhIn and CeRhIn have very
similar phase diagrams which contain both first- and second-order field-induced
magnetic transitions .Comment: 15 pages, 4 figure
Real-time gauge/gravity duality: Prescription, Renormalization and Examples
We present a comprehensive analysis of the prescription we recently put
forward for the computation of real-time correlation functions using
gauge/gravity duality. The prescription is valid for any holographic
supergravity background and it naturally maps initial and final data in the
bulk to initial and final states or density matrices in the field theory. We
show in detail how the technique of holographic renormalization can be applied
in this setting and we provide numerous illustrative examples, including the
computation of time-ordered, Wightman and retarded 2-point functions in
Poincare and global coordinates, thermal correlators and higher-point
functions.Comment: 85 pages, 13 figures; v2: added comments and reference
Pressure Induced Change in the Magnetic Modulation of CeRhIn5
We report the results of a high pressure neutron diffraction study of the
heavy fermion compound CeRhIn5 down to 1.8 K. CeRhIn5 is known to order
magnetically below 3.8 K with an incommensurate structure. The application of
hydrostatic pressure up to 8.6 kbar produces no change in the magnetic wave
vector qm. At 10 kbar of pressure however, a sudden change in the magnetic
structure occurs. Although the magnetic transition temperature remains the
same, qm increases from (0.5, 0.5, 0.298) to (0.5, 0.5, 0.396). This change in
the magnetic modulation may be the outcome of a change in the electronic
character of this material at 10 kbar.Comment: 4 pages, 3 figures include
- …