We find that the chromomagnetic instability existing in neutral two-flavor color superconductivity at moderate densities is removed by the formation of an inhomogeneous condensate of charged gluons and the corresponding induction of a magnetic field. It is shown that this inhomogeneous ground state is energetically favored over a homogeneous one. The spontaneous induction of a magnetic field in a color superconductor at moderate densities can be of interest for the astrophysics of compact stellar objects exhibiting strong magnetic fields as magnetars.

We expound on the impact of extra sterile species on the ultra high energy neutrino fluxes in neutrino telescopes. We use three types of well-known flux ratios and compare the values of these flux ratios in the presence of sterile neutrinos, with those predicted by deviation from the tribimaximal mixing scheme. We show that in the upcoming neutrino telescopes, it is easy to confuse the signature of sterile neutrinos with that of the deviation from tribimaximal mixing. We also show that if the measured flux ratios acquire a value well outside the range predicted by the standard scenario with three active neutrinos only, it might be possible to tell the presence of extra sterile neutrinos by observing ultra high energy neutrinos in future neutrino telescopes.

By analyzing the data collected at the center-of-mass energy $E_{\mathrm{cm}}=3.773\mathrm{GeV}$ and below the $D\overline{D}$ meson pair production threshold with the BES-II detector at the BEPC Collider, we directly measured the observed non-$D\overline{D}$ cross section of $\psi (3770)$ decay to be ${\sigma }_{\psi (3770)\to \mathrm{non}\mathrm{\text{−}}D\overline{D}}^{\mathrm{obs}}=(0.95\pm 0.35\pm 0.29)\mathrm{nb}$ at $E_{\mathrm{cm}}=3.773\mathrm{GeV}$, and the branching fraction $BF[\psi (3770)\to \mathrm{non}\mathrm{\text{−}}D\overline{D}]=(13.4\pm 5.0\pm 3.6)\%$ for inclusive non-$D\overline{D}$ decay of $\psi (3770)$. We also determined the cross section for $D\overline{D}$ meson pair production to be ${\sigma }_{D\overline{D}}^{\mathrm{obs}}=(6.12\pm 0.37\pm 0.23)\mathrm{nb}$ at $E_{\mathrm{cm}}=3.773\mathrm{GeV}$.

The shear viscosity $\eta$ of QCD in the hadronic phase is computed by the coupled Boltzmann equations of pions and nucleons in low temperatures and low baryon-number densities. The $\eta$ to entropy density ratio $\eta /s$ maps out the nuclear gas-liquid phase transition by forming a valley tracing the phase transition line in the temperature-chemical potential plane. When the phase transition turns into a crossover, the $\eta /s$ valley gradually disappears. We suspect the general feature for a first-order phase transition is that $\eta /s$ has a discontinuity in the bottom of the $\eta /s$ valley. The discontinuity coincides with the phase transition line and ends at the critical point. Beyond the critical point, a smooth $\eta /s$ valley is seen. However, the valley could disappear further away from the critical point. The $\eta /s$ measurements might provide an alternative to identify the critical points.

Mixings of four-quark components in the nonsinglet scalar mesons are studied in the QCD sum rules. We propose a formulation to evaluate the cross correlators of $q\overline{q}$ and $qq\overline{q}\overline{q}$ operators and to define the mixings of different Fock states in the sum rule. It is applied to the nonsinglet scalar mesons, $a_0$ and $K_0^{*}$. It is found that the four-quark operators predict lower masses than the $q\overline{q}$ operators and that the four-quark states occupy about 70%–90% of the lowest mass states.

We analyze the static QCD potential $V_{\mathrm{QCD}}(r)$ in the distance region $0.1\mathrm{fm}\lesssim r\lesssim 1\mathrm{fm}$ using perturbative QCD and operator-product expansion (OPE) as basic theoretical tools. We assemble theoretical developments up to date and perform a solid and accurate analysis. The analysis consists of three major steps: (I) We study large-order behavior of the perturbative series of $V_{\mathrm{QCD}}(r)$ analytically. Higher-order terms are estimated by large-${\beta }_0$ approximation or by renormalization group, and the renormalization scale is varied around the minimal-sensitivity scale. A $“\mathrm{\text{Coulomb}}”+\mathrm{\text{linear}}$ potential can be identified with the scale-independent and renormalon-free part of the prediction and can be separated from the renormalon-dominating part. (II) In the frame of OPE, we define two types of renormalization schemes for the leading Wilson coefficient. One scheme belongs to the class of conventional factorization schemes. The other scheme belongs to a new class, which is independent of the factorization scale, derived from a generalization of the $\mathrm{\text{Coulomb}}+\mathrm{\text{linear}}$ potential of (I). The Wilson coefficient is free from IR renormalons and IR divergences in both schemes. We study properties of the Wilson coefficient and of the corresponding nonperturbative contribution $\delta E_{\mathrm{US}}(r)$ in each scheme. (III) We compare numerically perturbative predictions of the Wilson coefficient and lattice computations of $V_{\mathrm{QCD}}(r)$ when $n_l=0$. We confirm either correctness or consistency (within uncertainties) of the theoretical predictions made in (II). Then we perform fits to simultaneously determine $\delta E_{\mathrm{US}}(r)$ and $r_0{\Lambda }_{\overline{\mathrm{MS}}}^{3\mathrm{\text{−}}\mathrm{loop}}$ (relation between lattice scale and ${\Lambda }_{\overline{\mathrm{MS}}}$). As for the former quantity, we improve bounds as compared to the previous determination; as for the latter quantity, our analysis provides a new method for its determination. We find that (a) $\delta E_{\mathrm{US}}(r)=0$ is disfavored, and (b) $r_0{\Lambda }_{\overline{\mathrm{MS}}}^{3\mathrm{\text{−}}\mathrm{loop}}=0.574\pm 0.042$. We elucidate the mechanism for the sensitivities and examine sources of errors in detail.

We make new predictions of ${\sigma }_{p-\mathrm{air}}^{\mathrm{prod}}$, the proton-air inelastic production cross section, at $pp$ center-of-mass energies $0.1\lesssim \sqrt{s}\lesssim 100\mathrm{TeV}$, using high-energy predictions from a saturated Froissart bound parametrization of accelerator data on forward $\overline{p}p$ and $pp$ scattering amplitudes, together with Glauber theory. The parametrization of the $\overline{p}p$ and $pp$ cross sections incorporates analyticity constraints and unitarity, allowing accurate extrapolations to ultrahigh energies. Our predictions are in excellent agreement with available cosmic-ray extensive air shower measurements, both in magnitude and in energy dependence.

Detailed analyses of the WMAP data indicate possible oscillatory features in the primordial curvature perturbation, which moreover appears to be suppressed beyond the present Hubble radius. Such deviations from the usual inflationary expectation of an approximately Harrison-Zeldovich spectrum are expected in the supergravity-based “multiple inflation” model wherein phase transitions during inflation induce sudden changes in the mass of the inflaton, thus interrupting its slow roll. In a previous paper we calculated the resulting curvature perturbation and showed how the oscillations arise. Here we perform a Markov chain Monte Carlo fitting exercise using the 3-year WMAP data to determine how the fitted cosmological parameters vary when such a primordial spectrum is used as an input, rather than the usually assumed power-law spectrum. The concordance $\Lambda \mathrm{CDM}$ model is still a good fit when there is just a step in the spectrum. However, if there is a bump in the spectrum (due e.g. to two phase transitions in rapid succession), the precision cosmic microwave background data can be well fitted by a flat Einstein-de Sitter cosmology without dark energy. This however requires the Hubble constant to be $h\simeq 0.44$ which is lower than the locally measured value. To fit the Sloane Digital Sky Survey data on the power spectrum of galaxy clustering requires a $\sim 10\%$ component of hot dark matter, as would naturally be provided by 3 species of neutrinos of mass $\sim 0.5\mathrm{eV}$. This $\mathrm{\text{cold}}+\mathrm{\text{hot dark matter}}$ model cannot however fit the position of the baryon acoustic peak in the luminous red galaxies redshift two-point correlation function. It may be possible to overcome these difficulties in an inhomogeneous Lemaître-Tolman-Bondi cosmological model with a local void, which can potentially also account for the SN Ia Hubble diagram without invoking cosmic acceleration.

We discuss the limit $T\to 0$ of the relativistic ideal Fermi gas of luxons (particles moving with the speed of light) and tachyons (hypothetical particles faster than light) based on observations of our recent paper: K. Kowalski, J. Rembieliński, and K. A. Smoliński, Phys. Rev. D 76, 045018 (2007). For bradyons this limit is in fact the nonrelativistic one and therefore it is not studied herein.

In a recent paper [B. Acharya, K. Bobkov, G. Kane, P. Kumar, and D. Vaman, Phys. Rev. Lett. 97, 191601 (2006).] it was shown that in fluxless $M$ theory vacua with at least two hidden sectors undergoing strong gauge dynamics and a particular form of the Kähler potential, all moduli are stabilized by the effective potential and a stable hierarchy is generated, consistent with standard gauge unification. This paper explains the results of [B. Acharya, K. Bobkov, G. Kane, P. Kumar, and D. Vaman, Phys. Rev. Lett. 97, 191601 (2006).] in more detail and generalizes them, finding an essentially unique de Sitter vacuum under reasonable conditions. One of the main phenomenological consequences is a prediction which emerges from this entire class of vacua: namely, gaugino masses are significantly suppressed relative to the gravitino mass. We also present evidence that, for those vacua in which the vacuum energy is small, the gravitino mass, which sets all the superpartner masses, is automatically in the TeV–100 TeV range.

The Pierre Auger Observatory (PAO) has measured the spectrum and composition of the ultrahigh energy cosmic rays with unprecedented precision. We use these measurements to constrain their spectrum and composition as injected from their sources and, in turn, use these results to estimate the spectrum of cosmogenic neutrinos generated in their propagation through intergalactic space. We find that the PAO spectrum and elongation rate measurements can be well fitted if the injected cosmic rays consist entirely of nuclei with masses in the intermediate (carbon, nitrogen, or oxygen) to heavy (iron, silicon) range. A mixture of protons and heavier species is also acceptable but (on the basis of existing hadronic interaction models) injection of pure light nuclei (protons, helium) results in unacceptable fits to the new elongation rate data. The expected spectrum of cosmogenic neutrinos can vary considerably, depending on the precise spectrum and chemical composition injected from the cosmic ray sources. In the models where heavy nuclei dominate the cosmic ray spectrum and few dissociated protons exceed GZK energies, the cosmogenic neutrino flux can be suppressed by up to 2 orders of magnitude relative to the all-proton prediction, making its detection beyond the reach of current and planned neutrino telescopes. Other models consistent with the data, however, are proton-dominated with only a small (1%–10%) admixture of heavy nuclei and predict an associated cosmogenic flux within the reach of upcoming experiments. Thus a detection or nondetection of cosmogenic neutrinos can assist in discriminating between these possibilities.

We consider the possibility that the dark energy is made up of two or more independent components, each having a different equation of state. We fit the model with supernova and gamma-ray burst data from recent observations, and use the Markov Chain Monte Carlo technique to estimate the allowed parameter regions. We also use various model selection criteria to compare the two-component model with the $\Lambda \mathrm{CDM}$, one-component dark energy model with static or variable $w$ (XCDM) and other multicomponent models. We find that the two-component models can give a reasonably good fit to the current data. For some data sets, and depending somewhat on the model selection criteria, the two-component model can give a better fit to the data than XCDM with static $w$ and XCDM with variable $w$ parametrized by $w=w_0+w_{a}z/(1+z)$.

We propose an $SU(5)$ grand unified model with an invisible axion and the unification of the three coupling constants which is in agreement with the values, at $M_Z$, of $\alpha$, ${\alpha }_s$, and ${sin}^2{\theta }_W$. A discrete, anomalous, $Z_{13}$ symmetry implies that the Peccei-Quinn symmetry is an automatic symmetry of the classical Lagrangian protecting, at the same time, the invisible axion against possible semiclassical gravity effects. Although the unification scale is of the order of the Peccei-Quinn scale the proton is stabilized by the fact that in this model the standard model fields form the $SU(5)$ multiplets completed by new exotic fields and, also, because it is protected by the $Z_{13}$ symmetry.

Effective low energy models arising in the context of D-brane configurations with standard model (SM) gauge symmetry extended by several gauged Abelian factors are discussed. The models are classified according to their hypercharge embeddings consistent with the SM spectrum hypercharge assignment. Particular cases are analyzed according to their perspectives and viability as low energy effective field theory candidates. The resulting string scale is determined by means of a two-loop renormalization group calculation. Their implications in Yukawa couplings, neutrinos and flavor changing processes are also presented.

We discuss a possible interpretation of the $D_{s1}(2460)$ meson as a hadronic molecule—a bound state of $D^{*}$ and $K$ mesons. Using a phenomenological Lagrangian approach we determine the strong $D_{s1}\to D_s^{*}{\pi }^0$ and radiative $D_{s1}\to D_s\gamma$ decays. In order of magnitude, our results for the partial strong and radiative decay widths are consistent with previous calculations.

The possible existence of axionlike particles could lead to a new type of long-distance communication. In this work, basic antenna concepts are defined and a Friis-like equation is derived to facilitate long-distance link calculations. An example calculation is presented showing that communication over distances of 1000 km or more may be possible for $m_a<3.5\mathrm{meV}$ and $g_{a\gamma \gamma }>5\times {10}^{-8}{\mathrm{GeV}}^{-1}$.

We present simple string models which dynamically break supersymmetry without non-Abelian gauge dynamics. The Fayet model, the Polonyi model, and the O’Raifeartaigh model each arise from D-branes at a specific type of singularity. D-brane instanton effects generate the requisite exponentially small scale of supersymmetry breaking.

A free quantum field in $1+1$ dimensions admits unitary Schrödinger picture dynamics along any foliation of spacetime by Cauchy curves. Kuchař showed that the Schrödinger picture state vectors, viewed as functionals of spacelike embeddings, satisfy a functional Schrödinger equation in which the generators of time evolution are the field energy-momentum densities with a particular normal-ordering and with a (nonunique) $c$-number contribution. The $c$-number contribution to the Schrödinger equation, called the “anomaly potential,” is needed to make the equation integrable in light of the Schwinger terms present in the commutators of the normal-ordered energy-momentum densities. Here we give a quantum geometric interpretation of the anomaly potential. In particular, we show the anomaly potential corresponds to the expression in a gauge of the natural connection on the bundle of vacuum states over the space of embeddings of Cauchy curves into the spacetime. The holonomy of this connection is the geometric phase associated with dynamical evolution along a closed path in the space of embeddings generated by the normal-ordered energy-momentum densities. The presence of the anomaly potential in the functional Schrödinger equation provides a dynamical phase which removes this holonomy, so that there is no net phase change for quantum transport around closed loops in the space of embeddings.

We discuss a nonminimal Einstein-Yang-Mills-Higgs model with uniaxial anisotropy in the group space associated with the Higgs field. We apply this theory to the problem of propagation of color and color-acoustic waves in the gravitational background related to the nonminimal regular Wu-Yang monopole.

The variety of ideas put forward in the context of a composite picture for the Higgs boson calls for a simple and effective description of the related phenomenology. Such a description is given here by means of a minimal model and is explicitly applied to the example of a Higgs-top sector from an $SO(5)$ symmetry. We discuss the spectrum, the electroweak precision tests, B-physics, and naturalness. We show the difficulty in complying with the different constraints. The extended gauge sector relative to the standard $SU(2)\times U(1)$, if there is any, has little or no impact on these considerations. We also discuss the relation of the minimal model with its “little Higgs” or holographic extensions based on the same symmetry.