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We present results for the QCD Equation of State at non-zero chemical potentials corresponding to the conserved charges in QCD using Taylor expansion upto sixth order in the baryon number, electric charge and strangeness chemical potentials. The latter two are constrained by the strangeness neutrality and a fixed electric charge to baryon number ratio. In our calculations, we use the Highly Improved Staggered Quarks (HISQ) discretization scheme at physical quark masses and at different values of the lattice spacings to control lattice cut-off effects. Furthermore we calculate the pressure along lines of constant energy density, which serve as proxies for the freeze-out conditions and discuss their dependence on $\mu_B$ , which is necessary for hydrodynamic modelling near freezeout. We also provide an estimate of the radius of convergence of the Taylor series from the 6th order coefficients which provides a new constraint on the location of the critical end-point in the T-$\mu_B$ plane of the QCD phase diagram., Comment: 4 pages, 5 figures, Proceedings of Quark Matter 2017

We propose a classical SU(2) gauge field in a flavor-space locked configuration as a species of radiation in the early universe, and show that it would have a significant imprint on a primordial stochastic gravitational wave spectrum. In the flavor-space locked configuration, the electric and magnetic fields of each flavor are parallel and mutually orthogonal to other flavors, with isotropic and homogeneous stress-energy. Due to the non-Abelian coupling, the gauge field breaks the symmetry between left- and right-circularly polarized gravitational waves. This broken chiral symmetry results in a unique signal: non-zero cross correlation of the cosmic microwave background temperature and polarization, $TB$ and $EB$, both of which should be zero in the standard, chiral symmetric case. We forecast the ability of current and future CMB experiments to constrain this model. Furthermore, a wide range of behavior is shown to emerge, depending on the gauge field coupling, abundance, and allocation into electric and magnetic field energy density. The fluctuation power of primordial gravitational waves oscillates back and forth into fluctuations of the gauge field. In certain cases, the gravitational wave spectrum is shown to be suppressed or amplified by up to an order of magnitude depending on the initial conditions of the gauge field., Comment: 20 pages, 11 figures

A cosmological gauge field with isotropic stress-energy introduces parity violation into the behavior of gravitational waves. We show that a primordial spectrum of inflationary gravitational waves develops a preferred handedness, left- or right-circularly polarized, depending on the abundance and coupling of the gauge field during the radiation era. A modest abundance of the gauge field would induce parity-violating correlations of the cosmic microwave background temperature and polarization patterns that could be detected by current and future experiments., Comment: 5 pages, 6 figures

We investigate how the use of higher wavenumbers (smaller scales) in the galaxy clustering power spectrum influences cosmological constraints. We take into account uncertainties from nonlinear density fluctuations, (scale dependent) galaxy bias, and baryonic effects. Allowing for substantially model independent uncertainties through separate fit parameters in each wavenumber bin that also allow for the redshift evolution, we quantify strong gains in dark energy and neutrino mass leverage with increasing maximum wavenumber, despite marginalizing over numerous (up to 125) extra fit parameters. The leverage is due to not only an increased number of modes but, more significantly, breaking of degeneracies beyond the linear regime., Comment: 10 pages, 6 figures

The dark sector of the Universe need not be completely separable into distinct dark matter and dark energy components. We consider a model of early dark energy in which the dark energy mimics a dark matter component in both evolution and perturbations at early times. Barotropic aether dark energy scales as a fixed fraction, possibly greater than one, of the dark matter density and has vanishing sound speed at early times before undergoing a transition. This gives signatures not only in cosmic expansion but in sound speed and inhomogeneities, and in number of effective neutrino species. Model parameters describe the timing, sharpness of the transition, and the relative abundance at early times. Upon comparison with current data, we find viable regimes in which the dark energy behaves like dark matter at early times: for transitions well before recombination the dark energy to dark matter fraction can equal or exceed unity, while for transitions near recombination the ratio can only be a few percent. After the transition, dark energy goes its separate way, ultimately driving cosmic acceleration and approaching a cosmological constant in this scenario., Comment: 10 pages, 8 figures

A phenomenological model of dark energy that tracks the baryonic and cold dark matter at early times but resembles a cosmological constant at late times is explored. In the transition between these two regimes, the dark energy density drops rapidly as if it were a relic species that freezes out, during which time the equation of state peaks at +1. Such an adjustment in the dark energy density, as it shifts from scaling to potential-domination, could be the signature of a trigger mechanism that helps explain the late-time cosmic acceleration. We show that the non-negligible dark energy density at early times, and the subsequent peak in the equation of state at the transition, leave an imprint on the cosmic microwave background anisotropy pattern and the rate of growth of large scale structure. The model introduces two new parameters, consisting of the present-day equation of state and the redshift of the freeze-out transition. A Monte Carlo Markov Chain analysis of a ten-dimensional parameter space is performed to compare the model with pre-Planck cosmic microwave background, large scale structure and supernova data and measurements of the Hubble constant. We find that the transition described by this model could have taken place as late as a redshift z~400. We explore the capability of future cosmic microwave background and weak lensing experiments to put tighter constraints on this model. The viability of this model may suggest new directions in dark-energy model building that address the coincidence problem., Comment: 11 pages, 15 figures

We present results on the QCD equation of state, obtained with two different improved dynamical staggered fermion actions and almost physical quark masses. Lattice cut-off effects are discussed in detail as results for three different lattice spacings are available now, i.e. results have been obtained on lattices with temporal extent of $N_\tau=4,6$ and 8. Furthermore we discuss the Taylor expansion approach to non-zero baryon chemical potential by means of an expansion of the pressure. We use the expansion coefficients to calculate various fluctuations and correlations among hadronic charges. We find that the correlations reproduce the qualitative behavior of the resonance gas model below $T_c$ and start to agree with the free gas predictions for $T\gsim 1.5T_c$., Comment: Invited talk given at 'Strong and ElectroWeak Matter', Amsterdam, the Netherlands, 26-29 August 2008; 8 pages, 5 figures

We present results on the QCD equation of state, obtained with two different improved dynamical staggered fermion actions and almost physical quark masses. Lattice cut-off effect are discussed in detail as results for three different lattice spacings are available now, i.e. results have been obtained on lattices with temporal extent of $N_\tau=4,6$ and 8. Furthermore we discuss the Taylor expansion approach to non-zero baryon chemical potential and present the isentropic equation of state on lines of constant entropy per baryon number., Comment: Invited talk given at the 3rd International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions, 8-14 June 2008, Illa da Toxa, Spain; 7 pages, 6 figures

We discuss the Taylor expansion approach to non-zero baryon chemical potential ($\mu_B$) and present results on expanion coefficients of the pressure and energy density up to the 6-th order in $\mu_B$. Calculations have been performed with (2+1)-flavor of improved staggerd fermions (p4fat3) and almost physical masses on lattices with temporal extent of four and six time slices. We use the expansion coefficients to construct the isentropic equation of state on lines of constant entropy per baryon number and various different hadronic fluctuations. Furthermore, we estimate the radius of convegence of our expansion, which can be seen as a method to analyze the structure of the QCD phase diagram., Comment: Combined Contribution of two presentations given at the XXVI International Symposium on Lattice Field Theory, Williamsburg, Virginia, USA, 2008 July 14-19; 11 pages, 6 figures

We present results on baryon number, strangeness and electric charge fluctuations in QCD at non-zero density and temperature obtained from lattice calculations with almost physical quark masses. At vanishing chemical potential, i.e. under conditions almost realized at RHIC and the LHC, quartic fluctuations of net baryon number and strangeness are large in a narrow temperature interval characterizing the transition region from the low to the high temperature phase. Our results are based on Taylor expansions in light and strange quark chemical potentials, i.e. we rigorously compute corrections to bulk thermodynamic quantities at non vanishing chemical potential, by performing a Taylor expansion in $\mu/T$. We find non-monotonic behavior for the radius of convergence of this series, which could be a hint for a critical end-point in the ($T,\mu$)-plane., Comment: 4 pages, 5 figures; to appear in the proceedings of the 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008), Jaipur, India, Feb 4-10, 2008

The frequency selectivity of wireless communication channels can be characterized by the delay spread Ds of the channel impulse response. If the delay spread is small compared to the bandwidth W of the input signal, that is, Ds*W approximately equal to 1, the channel appears to be flat fading. For Ds*W >> 1, the channel appears to be frequency selective, which is usually the case for wideband signals. In the first case, small scale synchronization with a precision much higher than the sampling time T = 1/W is crucial. In this paper, it is shown by analytical means that this is different in the wideband regime. Here synchronization with a precision of T is sufficient and small scale synchronization cannot further increase the captured energy at the receiver. Simulation results show that this effect already occurs for W > 50MHz for the IEEE 802.15.4a channel model., Comment: 5 pages. Changes from 2nd version: minor corrections. Essentially the paper to be presented at ISWCS 2008 in Reykjavik

The spatial string tension for 3+1 dimensional QCD at finite temperature is measured. The gauge configurations we re generated with two light and one heavier strange quark on lattices of size $16^3 4$ and $24^3 6$. This spatial string tension is compared with the string tension of the 3 dimensional pure gauge theory together with the temperature dependent 2-loop running coupling. Further comparison is made with predictions from dimensionally reduced effective theories.

We present results for screening masses of light and strange mesons in 2+1 flavour QCD using improved (p4fat3) staggered fermions on 6x24^3 lattices. We have studied the screening masses of scalar, pseudo-scalar, vector and axial-vector mesons along the line of constant physics, determined by a pion mass ~220 MeV and a kaon mass ~500 MeV. In order to investigate the cut-off and volume dependencies we have also performed studies of the meson screening correlators in the non-interacting theory using the p4 and the standard staggered discretizations.

We analyze the large-distance behaviour of static quark-anti-quark pair correlations in QCD. The singlet free energy is calculated and the entropy contribution to it is identified allowing us to calculate the excess internal energy. The free energy has a sharp drop in the critical region, leading to sharp peaks in both excess entropy and internal energy., Comment: talk given at Quark Matter 2006

The paper is devoted to the construction of low-energy quark scattering amplitudes. Bootstrap quark model allows to describe the light and heavy hadron spectroscopy based on three principles: unitarity, analicity and crossing symmetry. The resulting quark interaction appeared to be effectively short-range. This interaction is determined mainly by the exchange in the gluon channel: the constituent-gluon mass appeared to not be small. Our calculation indicates an important role of an interaction which is induced by instantons. Such an interaction is necessary for deriving both the pion mass and $\eta$-$\eta'$ mass splitting. However, due to the rules of $1/N_c$-expansion this interaction influences slightly the other channels while in the $\eta$-$\eta'$ channel it provides the correct values of masses and gives the angle of $\eta_1-\eta_8$ mixture close to that of the quark model. We discuss the possibility of constructing the amplitudes which take into account the quark confinement., Comment: LaTeX2e, 7 eps figures