215 research outputs found
Magnetic effects in a holographic Fermi-like liquid
We explore the magnetic properties of the Fermi-like liquid represented by
the D3-D7' system. The system exhibits interesting magnetic properties such as
ferromagnetism and an anomalous Hall effect, which are due to the Chern-Simons
term in the effective gravitational action. We investigate the spectrum of
quasi-normal modes in the presence of a magnetic field and show that the
magnetic field mitigates the instability towards a striped phase. In addition,
we find a critical magnetic field above which the zero sound mode becomes
massive.Comment: 18 pages, 15 figure
Quantum Hall Effect in a Holographic Model
We consider a holographic description of a system of strongly coupled
fermions in 2+1 dimensions based on a D7-brane probe in the background of
D3-branes, and construct stable embeddings by turning on worldvolume fluxes. We
study the system at finite temperature and charge density, and in the presence
of a background magnetic field. We show that Minkowski-like embeddings that
terminate above the horizon describe a family of quantum Hall states with
filling fractions that are parameterized by a single discrete parameter. The
quantization of the Hall conductivity is a direct consequence of the
topological quantization of the fluxes. When the magnetic field is varied
relative to the charge density away from these discrete filling fractions, the
embeddings deform continuously into black-hole-like embeddings that enter the
horizon and that describe metallic states. We also study the thermodynamics of
this system and show that there is a first order phase transition at a critical
temperature from the quantum Hall state to the metallic state.Comment: v2: 27 pages, 12 figures. There is a major revision in the
quantitative analysis. The qualitative results and conclusions are unchanged,
with one exception: we show that the quantum Hall state embeddings, which
exist for discrete values of the filling fraction, deform continuously into
metallic state embeddings away from these filling fraction
Fluctuations of a holographic quantum Hall fluid
We analyze the neutral spectrum of the holographic quantum Hall fluid
described by the D2-D8' model. As expected for a quantum Hall state, we find
the system to be stable and gapped and that, at least over much of the
parameter space, the lowest excitation mode is a magneto-roton. In addition, we
find magneto-rotons in higher modes as well. We show that these magneto-rotons
are direct consequences of level crossings between vector and scalar modes.Comment: 20 pages, 8 figures; v.2 figures improved, 2 figures added, and text
clarified particularly in Sec. 5, to appear in JHE
Holographic Conformal Window - A Bottom Up Approach
We propose a five-dimensional framework for modeling the background geometry
associated to ordinary Yang-Mills (YM) as well as to nonsupersymmetric gauge
theories possessing an infrared fixed point with fermions in various
representations of the underlying gauge group. The model is based on the
improved holographic approach, on the string theory side, and on the
conjectured all-orders beta function for the gauge theory one. We first analyze
the YM gauge theory. We then investigate the effects of adding flavors and show
that, in the holographic description of the conformal window, the geometry
becomes AdS when approaching the ultraviolet and the infrared regimes. As the
number of flavors increases within the conformal window we observe that the
geometry becomes more and more of AdS type over the entire energy range.Comment: 20 Pages, 3 Figures. v2: references adde
Long-term effect of xylitol chewing gum on dental caries
– About 85% ( n = 269) of the subjects who participated in the Ylivieska follow-up studies on the effect of xylitol chewing gum on dental caries during 1982–84 or 1982–85 were re-examined in 1987 for the analysis of possible long-term preventive effects. Further caries reduction was found 2 or 3 yr after the discontinuation of the use of xylitol. The effect was especially marked in girls; the reduction in caries increment in the post-use years was 60% for the 2-yr users, suggesting that more pronounced caries reduction was associated with the most regular use of xylitol. In teeth erupting during the first year of the use of xylitol gum the long-term preventive effect was greater than in other teeth. Several explanations are suggested: lasting effect of the microbiological changes in the mouth, bacterial colonization on newly erupted teeth by organisms other than S. mutatis , and/or thorough maturation of the teeth under favorable physico-chemical circumstances. The results suggest that the value of xylitol in caries prevention depends on the timing of the treatment in relation to the development of the dentitionPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75700/1/j.1600-0528.1989.tb00611.x.pd
Striped instability of a holographic Fermi-like liquid
We consider a holographic description of a system of strongly-coupled
fermions in 2+1 dimensions based on a D7-brane probe in the background of
D3-branes. The black hole embedding represents a Fermi-like liquid. We study
the excitations of the Fermi liquid system. Above a critical density which
depends on the temperature, the system becomes unstable towards an
inhomogeneous modulated phase which is similar to a charge density and spin
wave state. The essence of this instability can be effectively described by a
Maxwell-axion theory with a background electric field. We also consider the
fate of zero sound at non-zero temperature.Comment: 16 pages, 9 figures; v2: added discussion and one figure. Typos
correcte
Thermodynamics of deformed AdS model with a positive/negative quadratic correction in graviton-dilaton system
By solving the Einstein equations of the graviton coupling with a real scalar
dilaton field, we establish a general framework to self-consistently solve the
geometric background with black-hole for any given phenomenological holographic
models. In this framwork, we solve the black-hole background, the corresponding
dilaon field and the dilaton potential for the deformed AdS model with a
positive/negative quadratic correction. We systematically investigate the
thermodynamical properties of the deformed AdS model with a positive and
negative quadratic correction, respectively, and compare with lattice QCD on
the results of the equation of state, the heavy quark potential, the Polyakov
loop and the spatial Wilson loop. We find that the bulk thermodynamical
properties are not sensitive to the sign of the quadratic correction, and the
results of both deformed holographic QCD models agree well with lattice QCD
result for pure SU(3) gauge theory. However, the results from loop operators
favor a positive quadratic correction, which agree well with lattice QCD
result. Especially, the result from the Polyakov loop excludes the model with a
negative quadratic correction in the warp factor of .Comment: 26 figures,36 pages,V.3: an appendix,more equations and references
added,figures corrected,published versio
Thermodynamics of SU(N) Yang-Mills theories in 2+1 dimensions II - The deconfined phase
We present a non-perturbative study of the equation of state in the
deconfined phase of Yang-Mills theories in D=2+1 dimensions. We introduce a
holographic model, based on the improved holographic QCD model, from which we
derive a non-trivial relation between the order of the deconfinement phase
transition and the behavior of the trace of the energy-momentum tensor as a
function of the temperature T. We compare the theoretical predictions of this
holographic model with a new set of high-precision numerical results from
lattice simulations of SU(N) theories with N=2, 3, 4, 5 and 6 colors. The
latter reveal that, similarly to the D=3+1 case, the bulk equilibrium
thermodynamic quantities (pressure, trace of the energy-momentum tensor, energy
density and entropy density) exhibit nearly perfect proportionality to the
number of gluons, and can be successfully compared with the holographic
predictions in a broad range of temperatures. Finally, we also show that, again
similarly to the D=3+1 case, the trace of the energy-momentum tensor appears to
be proportional to T^2 in a wide temperature range, starting from approximately
1.2 T_c, where T_c denotes the critical deconfinement temperature.Comment: 2+36 pages, 10 figures; v2: comments added, curves showing the
holographic predictions included in the plots of the pressure and energy and
entropy densities, typos corrected: version published in JHE
On thermodynamics of N=6 superconformal Chern-Simons theory
We study thermodynamics of N=6 superconformal Chern-Simons theory by
computing quantum corrections to the free energy. We find that in weakly
coupled ABJM theory on R(2) x S(1), the leading correction is non-analytic in
the 't Hooft coupling lambda, and is approximately of order lambda^2
log(lambda)^3. The free energy is expressed in terms of the scalar thermal mass
m, which is generated by screening effects. We show that this mass vanishes to
1-loop order. We then go on to 2-loop order where we find a finite and positive
mass squared m^2. We discuss differences in the calculation between Coulomb and
Lorentz gauge. Our results indicate that the free energy is a monotonic
function in lambda which interpolates smoothly to the N^(3/2) behaviour at
strong coupling.Comment: 29 pages. v2: references added. v3: minor changes, references added,
published versio
Holographic aspects of three dimensional QCD from string theory
We study two aspects of 3D QCD with massless fermions in a holographic set-up
from string theory, based on D3/D7 branes; parity anomaly and baryons as baby
Skyrmions. We first give a novel account of parity anomaly of 3D QCD with odd
number of flavors from the IR holographic viewpoint by observing a subtle point
in D7 brane embeddings with a given fixed UV theory. We also discuss its UV
origin in terms of weakly coupled D-brane pictures. We then focus on the
parity-symmetric case of even number of N_F flavors, and study baryons in the
holographic model. We identify the monopoles of U(N_F) gauge theory dynamically
broken down to U(N_F/2)x U(N_F/2) in the holographic 4 dimensional bulk as a
holographic counter-part of 3D baby-Skyrmions for baryons in large N limit, and
work out some details how the mapping goes. In particular, we show that the
correct baryon charges emerge from the Witten effect with a space-varying theta
angle.Comment: 33 pages, 10 figures; v2: references added with comments, typos
corrected; v3: more references added; v4: holographic baryon profile and the
analysis of its baryon charge is significantly revised, correcting errors in
the previous discussio
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