The Skyrme model, an effective low energy theory rooted in large $N_c$ QCD, has been applied to the study of dense matter. Matter is described by various crystal structures of Skyrmions. When this system is heated, the dominating thermal degrees of freedom are the fluctuating pions. Taking these mechanisms jointly produces a description of the chiral phase transition leading to the conventional phase diagram with critical temperatures and densities in agreement with expected values.

We use the soft-wall anti–de Sitter/QCD model to investigate the finite-temperature effects on the spectral function in the vector channel. The dissociation of the vector meson tower onto the anti–de Sitter black hole leads to the in-medium mass shift and the width broadening in a way similar to the lattice QCD results for the heavy quarkonium at finite temperature. We also show the momentum dependence of the spectral function and find it consistent with screening in a hot wind.

We present a calculation of the $N$ to $\Delta$ electromagnetic transition amplitudes using the method of QCD sum rules. A complete set of QCD sum rules is derived for the entire family of transitions from the baryon octet to decuplet. They are analyzed in conjunction with the corresponding mass sum rules using a Monte Carlo-based analysis procedure. The performance of each of the sum rules is examined using the criteria of operator product expansion convergence and ground-state dominance, along with the role of the transitions in intermediate states. Individual contributions from the $u$, $d$, and $s$ quarks are isolated and their implications in the underlying dynamics are explored. Valid sum rules are identified and their predictions are obtained. The results are compared with experiment and other calculations.

The analysis of data sometimes requires fitting many free parameters in a theory to a large number of data points. Questions naturally arise about the compatibility of specific subsets of the data, such as those from a particular experiment or those based on a particular technique, with the rest of the data. Questions also arise about which theory parameters are determined by specific subsets of the data. I present a method to answer both of these kinds of questions. The method is illustrated by applications to recent work on measuring parton distribution functions.

The cross sections for $e^{+}{e}^{-}\to \varphi {\pi }^{+}{\pi }^{-}$ and $e^{+}{e}^{-}\to \varphi f_0(980)$ are measured from threshold to $\sqrt{s}=3.0\mathrm{GeV}$ using initial-state radiation. The analysis is based on a data sample of $673{\mathrm{fb}}^{-1}$ collected on and below the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. First measurements are reported for the resonance parameters of the $\varphi (1680)$ in the $\varphi {\pi }^{+}{\pi }^{-}$ mode: $m=(1689\pm 7\pm 10)\mathrm{MeV}/c^2$ and $\Gamma =(211\pm 14\pm 19)\mathrm{MeV}/c^2$. A structure at $\sqrt{s}=2.1\mathrm{GeV}/c^2$, corresponding to the so called $Y(2175)$, is observed; its mass and width are determined to be $(2079\pm {13}_{-28}^{+79})\mathrm{MeV}/c^2$ and $(192\pm {23}_{-61}^{+25})\mathrm{MeV}/c^2$, respectively.

We consider an action that can generate fluids with three unequal stresses for metrics with a spacelike Killing vector. The parameters in the action are directly related to the stress anisotropies. The field equations following from the action are applied to an anisotropic cosmological expansion and an extension of the Gott-Hiscock cosmic string.

We propose a qualitatively new mechanism for generating cosmological fluctuations from inflation. The nonequilibrium excitation of interacting scalar fields often evolves into infrared (IR) and ultraviolet cascading, resulting in an intermediate scaling regime. We observe elements of this phenomenon in a simple model with inflaton $\varphi$ and isoinflaton $\chi$ fields interacting during inflation via the coupling $g^2(\varphi -{\varphi }_0{)}^2{\chi }^2$. Isoinflaton particles are created during inflation when they become instantaneously massless at $\varphi ={\varphi }_0$, with occupation numbers not exceeding unity. Previous studies have focused on the momentary slowing down of the condensate $\varphi (t)$ by back-reaction effects. Here, we point out that very quickly the produced $\chi$ particles become heavy and their multiple rescatterings off the homogeneous condensate $\varphi (t)$ generates Bremsstrahlung radiation of light inflaton IR fluctuations with high occupation numbers. The subsequent evolution of these IR fluctuations is qualitatively similar to that of the usual inflationary fluctuations, but their initial amplitude is different. The IR cascading generates a bump-shaped contribution to the cosmological curvature fluctuations, which can even dominate over the usual fluctuations for $g^2>0.06$. The IR cascading curvature fluctuations are significantly non-Gaussian, and the strength and location of the bump are model dependent, through $g^2$ and ${\varphi }_0$. The effect from IR cascading fluctuations is significantly larger than that from the momentary slowing down of $\varphi (t)$. With a sequence of such bursts of particle production, the superposition of the bumps can lead to a new broadband non-Gaussian component of cosmological fluctuations added to the usual fluctuations. Such a sequence of particle creation events can, but need not, lead to trapped inflation.

We determine the $O({\alpha }_s)$ radiative corrections to polarized top quark pair production in $e^{+}{e}^{-}$ annihilations with a specified gluon energy cut. We write down fully analytical results for the unpolarized and polarized $O({\alpha }_s)$ cross sections $e^{+}{e}^{-}\to \overline{t}t(G)$ and $e^{+}{e}^{-}\to \overline{t}{t}^{\uparrow }(G)$ including their polar orientation dependence relative to the beam direction. In the soft-gluon limit we recover the usual factorizing form known from the soft-gluon approximation. In the limit when the gluon energy cut takes its maximum value we recover the totally inclusive unpolarized and polarized cross sections calculated previously. We provide some numerical results on the cutoff dependence of the various polarized and unpolarized cross sections and discuss how the exact results numerically differ from the approximate soft-gluon results.

Spin and polarization effects and correlations between them in the processes of pair production by a photon and synchrotron radiation in a magnetic field are considered. Expressions for the probabilities of the processes with arbitrary polarizations of the particles are obtained. These expressions are analyzed in detail in both the lowest Landau levels and ultrarelativistic approximations.

We derive a closed form expression for the sum of all the infrared divergent contributions to the free energy of a gas of gravitons. An important ingredient of our calculation is the use of a gauge fixing procedure such that the graviton propagator becomes both traceless and transverse. This has been shown to be possible, in a previous work, using a general gauge fixing procedure, in the context of the lowest order expansion of the Einstein-Hilbert action, describing noninteracting spin-two fields. In order to encompass the problems involving thermal loops, such as the resummation of the free energy, in the present work, we have extended this procedure to the situations when the interactions are taken into account.

The evolution of the spectrum of cosmological fluctuations from one cycle to the next is studied. It is pointed out that each cycle leads to a reddening of the spectrum. This opens up new ways to generate a scale-invariant spectrum of curvature perturbations. The large increase in the amplitude of the fluctuations quickly leads to a breakdown of the linear theory. More generally, we see that, after including linearized cosmological perturbations, a cyclic universe cannot be truly cyclic.

We investigate recent claims that brane inflation solves the overshoot problem through a combination of microphysical restrictions on the phase space of initial conditions and the existence of the Dirac-Born-Infeld attractor in regimes where the slow-roll attractor does not apply. Carrying out a comprehensive analysis of the parameter space allowed by the latest advances in brane inflation model-building, we find that these restrictions are insufficient to solve the overshoot problem. The vast majority of the phase space of initial conditions is still dominated by overshoot trajectories. We present an analytic proof that the brane-inflationary attractor must be close to the slow-roll limit, and update the predictions for observables such as non-Gaussianity, cosmic string tension, and tensor modes.

Superconducting cosmic strings naturally emit highly boosted charge carriers from cusps. This occurs when a cosmic string or a loop moves through a magnetic field and develops an electric current. The charge carriers and the products of their decay, including protons, photons, and neutrinos, are emitted as narrow jets with opening angle $\theta \sim 1/{\gamma }_c$, where ${\gamma }_c$ is the Lorentz factor of the cusp. The excitation of electric currents in strings occurs mostly in clusters of galaxies, which are characterized by magnetic fields $B\sim {10}^{-6}\mathrm{G}$ and a filling factor $f_B\sim {10}^{-3}$. Two string parameters determine the emission of the particles: the symmetry breaking scale $\eta$, which for successful applications should be of order ${10}^9–{10}^{12}\mathrm{GeV}$, and the dimensionless parameter $i_c$, which determines the maximum induced current as $J_{\max }=i_{c}e\eta$ and the energy of emitted charge carriers as ${ϵ}_X\sim i_c{\gamma }_c\eta$, where $e$ is the electric charge of a particle. For the parameters $\eta$ and $B$ mentioned above, the Lorentz factor reaches ${\gamma }_c\sim {10}^{12}$ and the maximum particle energy can be as high as ${\gamma }_c\eta \sim {10}^{22}\mathrm{GeV}$. The diffuse fluxes of ultrahigh energy neutrinos are close to the cascade upper limit, and can be detected by future neutrino observatories. The signatures of this model are: very high energies of neutrinos, in excess of ${10}^{20}\mathrm{eV}$; correlation of neutrinos with clusters of galaxies; simultaneous appearance of several neutrino-produced showers in the field of view of very large detectors, such as JEM-EUSO; and 10 TeV gamma radiation from the Virgo cluster. The flux of ultrahigh energy protons from cusps may account for a large fraction of the observed events at the highest energies.

We examine various possibilities for realistic 5D Higgsless models on a Randall-Sundrum (RS) background, and construct a full quark sector featuring next-to-minimal flavor violation (with an exact bulk $SU(2)$ protecting the first two generations) which satisfies electroweak and flavor constraints. The “new custodially protected representation” is used for the third generation to protect the light quarks from flavor violations induced due to the heavy top. A combination of flavor symmetries, and an “RS-GIM” mechanism for the right-handed quarks suppresses flavor-changing neutral currents below experimental bounds, assuming Cabibbo-Kobayashi-Maskawa–type mixing on the UV brane. In addition to the usual Higgsless RS signals, this model predicts an exotic charge-$5/3$ quark with mass of about 0.5 TeV which should show up at the LHC very quickly, as well as nonzero flavor-changing neutral currents which could be detected in the next generation of flavor experiments. In the course of our analysis, we also find quantitative estimates for the errors of the fermion zero-mode approximation, which are significant for Higgsless-type models.

We consider a solution to the $\mu$ problem in the context of nonminimal gauge mediation with two singlets and low-scale messengers. This solution reduces tuning associated with the “little hierarchy” problem by permitting a naturally small $\mu$ term, $\mathcal{O}(100–300\mathrm{GeV})$, due to small mixing between the singlets. The smallness of $\mu$ also relies crucially on compressing the gauge mediated sparticle spectrum resulting in 330–400 GeV squarks. In addition to a small $\mu$ term, the theory achieves $m_{\mathrm{Higgs}}>114.4\mathrm{GeV}$ through a large Higgs quartic coupling when $\tan \beta \sim 1.5$. The vacua studied are globally stable with all couplings perturbative to the grand unified theory scale. The amount of tuning required to get the correct electroweak scale is $\mathcal{O}(10\%)$, with a similar residual tuning associated with the region of parameter space where the lightest $CP$-even Higgs mass is above the LEP bound.

In this paper, we investigate deep inelastic and elastic scattering on a polarized spin-$\frac{1}{2}$ hadron using gauge/string duality. This spin-$\frac{1}{2}$ hadron corresponds to a supergravity mode of the dilatino. The polarized deep inelastic structure functions are computed in the supergravity approximation at large t’ Hooft coupling $\lambda$ and finite $x$ with ${\lambda }^{-1/2}\ll x<1$. Furthermore, we discuss the moments of all structure functions, and propose an interesting sum rule ${\int }_0^{1}dx{g}_2(x,q^2)=0$ for the $g_2$ structure function which is known as the Burkhardt-Cottingham sum rule in QCD. In the end, the elastic scattering is studied and elastic form factors of the spin-$\frac{1}{2}$ hadron are calculated within the same framework.

Half-life estimates for neutrinoless double beta decay depend on particle physics models for lepton-flavor violation, as well as on nuclear physics models for the structure and transitions of candidate nuclei. Different models considered in the literature can be contrasted—via prospective data—with a “standard” scenario characterized by light Majorana neutrino exchange and by the quasiparticle random phase approximation, for which the theoretical covariance matrix has been recently estimated. We show that, assuming future half-life data in four promising nuclei (${}^{76}\mathrm{Ge}$, ${}^{82}\mathrm{Se}$, ${}^{130}\mathrm{Te}$, and ${}^{136}\mathrm{Xe}$), the standard scenario can be distinguished from a few nonstandard physics models, while being compatible with alternative state-of-the-art nuclear calculations (at 95% C.L.). Future signals in different nuclei may thus help to discriminate at least some decay mechanisms, without being spoiled by current nuclear uncertainties. Prospects for possible improvements are also discussed.

We present a shortened and simplified version of our proof [C. S. Fischer and J. M. Pawlowski, Phys. Rev. D 75, 025012 (2007).] of the uniqueness of the scaling solution for the infrared asymptotics of Green functions in Landau gauge Yang-Mills theory. The simplification relates to a new renormalization group–invariant arrangement of Green functions applicable to general theories. As before the proof relies on the necessary consistency between Dyson-Schwinger equations and functional renormalization group equations. We also demonstrate the existence of a specific scaling solution for both, Dyson-Schwinger equations and functional renormalization group equations, that displays uniform and soft kinematic singularities.

We present numerical evidences for the validity of the inequality between the total mass and the total angular momentum for multiple axially symmetric (nonstationary) black holes. We use a parabolic heat flow to solve numerically the stationary axially symmetric Einstein equations. As a by-product of our method, we also give numerical evidences that there are no regular solutions of Einstein equations that describe two extreme, axially symmetric black holes in equilibrium.

We study axion cosmology in a 5D universe, in the case of flat and warped extra dimensions. The comparison between theoretical predictions and observations constrains the 5D axion decay constant and the 5D Planck mass, which have to be taken into account in building 5D axion models. The framework developed in this paper can be readily applied to other bulk fields in brane universes.