125 research outputs found

### On the QCD Phase Transition at Finite Baryon Density

We investigate the QCD chiral phase transition at finite chemical potential
$\mu$, using the renormalization group (RG) to characterize the infrared
behavior of sigma models constrained by the flavor and spacetime symmetries.
The results are similar to those obtained from RG analysis of the finite
temperature transition at zero baryon density. When there are more than two
massless flavors of quarks, a first order transition is predicted for the
entire phase boundary. In the two flavor case, a boundary with first and second
order regions separated by a tricritical point seems most likely. We discuss
the real-world case with two light quarks and an intermediate mass strange
quark. Improved lattice data on the temperature transition will strongly
constrain the possibilities for the phase boundary.Comment: 10 pages, 2 figures, Latex. Added discussion on realistic strange
quark mass and recent lattice dat

### Neutron Star Vortex Dynamics and Magnetic Field Decay: Implications for High Density Nuclear Matter

We investigate the effect of the density-dependent proton and neutron gaps on
vortex dynamics in neutron stars. We argue that the persistence of neutron star
magnetic fields on timescales of $10^9$ y suggests a superconducting gap curve
with local maximum at intermediate density. We discuss the implications for
exotic core phenomena such as pion/kaon condensation or a transition to quark
matter.Comment: 7 pages, 2 figures, uses LaTe

### On the volatility of volatility

The Chicago Board Options Exchange (CBOE) Volatility Index, VIX, is
calculated based on prices of out-of-the-money put and call options on the S&P
500 index (SPX). Sometimes called the "investor fear gauge," the VIX is a
measure of the implied volatility of the SPX, and is observed to be correlated
with the 30-day realized volatility of the SPX. Changes in the VIX are observed
to be negatively correlated with changes in the SPX. However, no significant
correlation between changes in the VIX and changes in the 30-day realized
volatility of the SPX are observed. We investigate whether this indicates a
mispricing of options following large VIX moves, and examine the relation to
excess returns from variance swaps.Comment: 15 pages, 12 figures, LaTe

### Cosmology of Nonlinear Oscillations

The nonlinear oscillations of a scalar field are shown to have cosmological
equations of state with $w = p / \rho$ ranging from $-1 < w < 1$. We
investigate the possibility that the dark energy is due to such oscillations.Comment: 5 pages, latex. References added; to appear in PL

### Gradient instability for Ï < - 1

We show that in single scalar field models of the dark energy with equations of state satisfying w âĄ p/Ï < â 1, the effective Lagrangian for fluctuations about the homogeneous background has a wrong sign spatial kinetic term. In most cases, spatial gradients are ruled out by microwave background observations. The sign of w + 1 is not connected to the sign of the time derivative kinetic term in the effective Lagrangian

### Instabilities and the null energy condition

We show that violation of the null energy condition implies instability in a
broad class of models, including classical gauge theories with scalar and
fermionic matter as well as any perfect fluid. When applied to the dark energy,
our results imply that $w = p / \rho$ is unlikely to be less than -1.Comment: 5 pages, 1 figure, revtex, presentation improved, minor change

### Magnetic Interactions, the Renormalization Group and Color Superconductivity in High Density QCD

We investigate the effect of long range magnetic interactions on the
renormalization group (RG) evolution of local Cooper pairing interactions near
the Fermi surface in high density QCD. We use an explicit cut-off on momentum
modes, with special emphasis on screening effects such as Landau damping, to
derive the RG equations in a gauge invariant, weak coupling expansion. We
obtain the Landau pole $\Delta \sim \mu g^{-5} \exp(- \frac{3 \pi^2}{\sqrt{2}
g})$, although the structure of our equations differs from previous results. We
also investigate the gap equation, including condensates of higher angular
momentum. We show that rotational invariance is unbroken at asymptotically high
density, and verify that $\Delta$ is the correct value of the gap when higher
modes are included in the analysis.Comment: 17 pages, 3 figures, late

### Anomaly Induced QCD Potential and Quark Decoupling

We explore the anomaly induced effective QCD meson potential in the framework of the effective Lagrangian approach. We suggest a decoupling procedure, when a flavored quark becomes massive, which mimics the one employed by Seiberg for supersymmetric gauge theories. It is seen that, after decoupling, the QCD potential naturally converts to the one with one less flavor. We study the N_c and N_f dependence of the \eta^{\prime} mass

### Black hole entropy, curved space and monsters

We investigate the microscopic origin of black hole entropy, in particular
the gap between the maximum entropy of ordinary matter and that of black holes.
Using curved space, we construct configurations with entropy greater than their
area in Planck units. These configurations have pathological properties and we
refer to them as monsters. When monsters are excluded we recover the entropy
bound on ordinary matter $S < A^{3/4}$. This bound implies that essentially all
of the microstates of a semiclassical black hole are associated with the growth
of a slightly smaller black hole which absorbs some additional energy. Our
results suggest that the area entropy of black holes is the logarithm of the
number of distinct ways in which one can form the black hole from ordinary
matter and smaller black holes, but only after the exclusion of monster states.Comment: 5 pages, revtex. Final version to appear Physics Letters

### A Note on Supersymmetry Breaking

Using a simple observation based on holomorphy, we argue that any model which
spontaneously breaks supersymmetry for some range of a parameter will do so
generically for all values of that parameter, modulo some isolated exceptional
points. Conversely, a model which preserves supersymmetry for some range of a
parameter will also do so everywhere except at isolated exceptional points. We
discuss how these observations can be useful in the construction of new models
which break supersymmetry and discuss some simple examples. We also comment on
the relation of these results to the Witten index.Comment: 10 pages, LaTeX. Additional reference added, minor change to last
subsectio

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