Lattice QCD at finite isospin density at zero and finite temperature

We simulate lattice QCD with dynamical $u$ and $d$ quarks at finite chemical potential, $\mu_I$, for the third component of isospin ($I_3$), at both zero and at finite temperature. At zero temperature there is some $\mu_I$, $\mu_c$ say, above which $I_3$ and parity are spontaneously broken by a charged pion condensate. This is in qualitative agreement with the prediction of effective (chiral) Lagrangians which also predict $\mu_c=m_\pi$. This transition appears to be second order, with scaling properties consistent with the mean-field predictions of such effective Lagrangian models. We have also studied the restoration of $I_3$ symmetry at high temperature for $\mu_I > \mu_c$. For $\mu_I$ sufficiently large, this finite temperature phase transition appears to be first order. As $\mu_I$ is decreased it becomes second order connecting continuously with the zero temperature transition.Comment: 23 pages, Revtex, 9 figures. Major revision of sections 3 and 4 to include new analyses of critical scaling which we now find to be in the universality class of mean-field theor

Fast Spherical Harmonic Analysis: a quick algorithm for generating and/or inverting full sky, high resolution CMB Anisotropy maps

We present a fast algorithm for generating full sky, high resolution ($\sim 5'$) simulations of the CMB anisotropy pattern. We also discuss the inverse problem, that of evaluating from such a map the full set of $a_{\ell m}$'s and the spectral coefficients $C_\ell$. We show that using an Equidistant Cylindrical Projection of the sky substantially speeds up the calculations. Thus, generating and/or inverting a full sky, high resolution map can be easily achieved with present day computer technology.Comment: 13 pages, LaTex, 5 PostScript figures included, 1 colour plate available (PostScript version, 1.6 Mb) at http://itovf2.roma2.infn.it/natoli

The pseudo-Goldstone spectrum of 2-colour QCD at finite density

We examine the spectrum of 2-colour lattice QCD with 4 continuum flavours at a finite chemical potential ($\mu$) for quark-number, on a $12^3 \times 24$ lattice. First we present evidence that the system undergoes a transition to a state with a diquark condensate, which spontaneously breaks quark number at $\mu=m_\pi/2$, and that this transition is mean field in nature. We then examine the 3 states that would be Goldstone bosons at $\mu=0$ for zero Dirac and Majorana quark masses. The predictions of chiral effective Lagrangians give a good description of the behaviour of these masses for $\mu < m_\pi/2$. Except for the heaviest of these states, these predictions diverge from our measurements, once $\mu$ is significantly greater than $m_\pi/2$. However, the qualitative behaviour of these masses, indicates that the physics is very similar to that predicted by these effective Lagrangians, and there is some indication that at least part of these discrepancies is due to saturation, a lattice artifact.Comment: 32 pages LaTeX/Revtex, 8 Postscript figure

SU(N) Quantum Antiferromagnets and the Phase Structure of QED in the Strong Coupling Limit

We examine the strong coupling limit of both compact and non compact QED on a lattice with staggered fermions. We show that every SU(N) antiferromagnet with spins in a particular fundamental representation of the SU(N) Lie Algebra and with nearest neighbor couplings on a bipartite lattice is exactly equivalent to the infinite coupling limit of lattice QED with the numbers of flavors of electrons related to N and the dimension of spacetime D+1. We find that,for both compact and noncompact QED,when N is odd the ground state of the strong coupling limit breaks chiral symmetry in any dimensions and for any N and the condensate is an isoscalar mass operator. When N is even,chiral symmetry is broken if D is bigger or equal to 2 and N is small enough and the order parameter is an isovector mass operator. We also find the exact ground state of the lattice Coulomb gas as well as a variety of related lattice statistical systems with long ranged interactions.Comment: latex, 45 pages, DFUPG 69/9

ARCADE: Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission

The Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE) is a balloon-borne instrument designed to measure the temperature of the cosmic microwave background at centimeter wavelengths. ARCADE searches for deviations from a blackbody spectrum resulting from energy releases in the early universe. Long-wavelength distortions in the CMB spectrum are expected in all viable cosmological models. Detecting these distortions or showing that they do not exist is an important step for understanding the early universe. We describe the ARCADE instrument design, current status, and future plans.Comment: 12 pages, 6 figures. Proceedings of the Fundamental Physics With CMB workshop, UC Irvine, March 23-25, 2006, to be published in New Astronomy Review

Light-front Quantized Chiral Schwinger Model and its Vacuum Structure

The bosonized Chiral Schwinger model (CSM) is quantized on the light-front (LF). The physical Hilbert space of CSM is obtained directly once the constraints on the LF phase space are eliminated. The discussion of the degenerate vacua and the absence in the CSM of the $\theta$-vacua, as found in the Schwinger model (SM), becomes straightforward. The differences in the structures of the the mass excitations and the vacua in these gauge theories are displayed transparently. The procedure followed is the one used successfully in the previous works for describing the spontaneous symmetry breaking (SSB) and the SM on the LF. The physical contents following from the LF quantized theory agree with those known in the conventional treatment. The LF hyperplane is argued to be equally appropriate as the conventional equal-time one for the canonical quantization. Some comments on the irrelevance, in quantized field theory, of the fact that the hyperplanes $x^{\pm}=0$ constitute characteristic surfaces of hyperbolic partial differential equation are also made.Comment: 12 pages, plain Late

On strongly coupled quenched QED4, again: chiral symmetry breaking, Goldstone mechanism and the nature of the continuum limit

We explore the possibility of a trivial continuum limit of strongly coupled quenched QED4 by contrasting our results with a Nambu--Jona Lasinio equation of state. The data does not compare favorably with such scenario. We study in detail the interplay of chiral symmetry breaking with the Goldstone mechanism, and clarify some puzzling features of past results.Comment: Contribution to Lat94, 3 pages, tar-compressed uuencoded ps fil

Quenched QCD at finite density: g=1g=1 and g=∞g=\infty

We report on our ongoing effort to understand quenched lattice QCD at finite baryon number density. The quenched theory is sensitive to the baryon mass both at strong coupling and in the scaling region. However, we find that the quenched model is pathological for $\mu > m_\pi/2$ at $\beta= 6.0$, in agreement with past Lanczos analyses of the Dirac operator.Comment: Contribution to Lat94, 3 pages, tar-compressed uuencoded ps fil

Cosmological constraints from CMB distortion

We examine bounds on adiabatic and isocurvature density fluctuations from $\mu$-type spectral distortions of the cosmic microwave background (CMB). Studies of such distortion are complementary to CMB measurements of the spectral index and its running, and will help to constrain these parameters on significantly smaller scales. We show that a detection on the order of $\mu \sim 10^{-7}$ would strongly be at odds with the standard cosmological model of a nearly scale-invariant spectrum of adiabatic perturbations. Further, we find that given the current CMB constraints on the isocurvature mode amplitude, a nearly scale-invariant isocurvature mode (common in many curvaton models) cannot produce significant $\mu$-distortion. Finally, we show that future experiments will strongly constrain the amplitude of the isocurvature modes with a highly blue spectrum as predicted by certain axion models.Comment: 6 pages, 4 figures, version 3 contains a new figure showing the contribution to \mu_k as a function of k, and a clarification regarding the acoustic wave energy, accompanied by a related acknowledgement and referenc

Pathologies of Quenched Lattice QCD at non--zero Density and its Effective Potential

We simulate lattice QCD at non--zero baryon density and zero temperature in the quenched approximation, both in the scaling region and in the infinite coupling limit. We investigate the nature of the forbidden region -- the range of chemical potential where the simulations grow prohibitively expensive, and the results, when available, are puzzling if not unphysical. At weak coupling we have explored the sensitivity of these pathologies to the lattice size, and found that using a large lattice ($64 \times 16^3$) does not remove them. The effective potential sheds considerable light on the problems in the simulations, and gives a clear interpretation of the forbidden region. The strong coupling simulations were particularly illuminating on this point.Comment: 49 pages, uu-encoded expanding to postscript;also available at ftp://hlrz36.hlrz.kfa-juelich.de/pub/mpl/hlrz72_95.p