We show that in a general class of strongly interacting theories at high temperatures the speed of sound approaches the conformal value $c_s^2=1/3$ universally from below. This class includes theories holographically dual to a theory of gravity coupled to a single scalar field, representing the operator of the scale anomaly.

We propose a new framework unifying cold dark matter (CDM) and modified Newtonian dynamics (MOND) to solve their respective problems on galactic scales and large scale structure formation. In our framework the dark matter clusters on large scales but not on galactic scales. This environment dependence of the dark matter behaviors is controlled by a vector field, which also produces the MOND effects in galaxies. We find that in this framework only a single mass scale needs to be introduced to produce the phenomena of CDM, MOND, and also dark energy.

We present a detailed systematics for comparing warped brane inflation with the observations, incorporating the effects of both moduli stabilization and ultraviolet bulk physics. We explicitly construct an example of the inflaton potential governing the motion of a mobile D3 brane in the entire warped deformed conifold. This allows us to precisely identify the corresponding scales of the cosmic microwave background. The effects due to bulk fluxes or localized sources are parametrized using gauge/string duality. We next perform some sample scannings to explore the parameter space of the complete potential, and first demonstrate that without the bulk effects there can be large degenerate sets of parameters with observationally consistent predictions. When the bulk perturbations are included, however, the observational predictions are generally spoiled. For them to remain consistent, the magnitudes of the additional bulk effects need to be highly suppressed.

We examine the nature of the cosmological Big Bounce transition within the loop geometry underlying loop quantum cosmology at classical and quantum levels. Our canonical quantization method is an alternative to the standard loop quantum cosmology. An evolution parameter we use has a clear interpretation. Our method opens the door for analyses of spectra of physical observables like the energy density and the volume operator. We find that one cannot determine the energy scale specific to the Big Bounce by making use of the loop geometry without an extra input from observational cosmology.

We discuss a novel explanation of the dark energy as a manifestation of macroscopic nonlocality coming from quantum gravity, as proposed by Markopoulou [F. Markopoulou (private communication)]. It has been previously suggested that in a transition from an early quantum geometric phase of the Universe to a low temperature phase characterized by an emergent spacetime metric, locality might have been “disordered.” This means that there is a mismatch of micro-locality, as determined by the microscopic quantum dynamics and macro-locality as determined by the classical metric that governs the emergent low energy physics. In this paper we discuss the consequences for cosmology by studying a simple extension of the standard cosmological models with disordered locality. We show that the consequences can include a naturally small vacuum energy.

We show that the common singularities present in generic modified gravity models governed by actions of the type $S=\int d^{4}x\sqrt{-g}f(R,\varphi ,X)$, with $X=-\frac{1}{2}{g}^{ab}{\partial }_a\varphi {\partial }_b\varphi$, are essentially the same anisotropic instabilities associated to the hypersurface $F(\varphi )=0$ in the case of a nonminimal coupling of the type $F(\varphi )R$, enlightening the physical origin of such singularities that typically arise in rather complex and cumbersome inhomogeneous perturbation analyses. We show, moreover, that such anisotropic instabilities typically give rise to dynamically unavoidable singularities, precluding completely the possibility of having physically viable models for which the hypersurface $\frac{\partial f}{\partial R}=0$ is attained. Some examples are explicitly discussed.

Instead of using a three-dimensional analysis on quasilocal horizons, we adopt a four-dimensional asymptotic expansion analysis to study the next order contributions from the nonlinearity of general relativity. From the similarity between null infinity and horizons, the proper reference frames are chosen from the compatible constant spinors for an observer to measure the energy-momentum and flux near quasilocal horizons. In particular, we focus on the similarity of Bondi-Sachs gravitational radiation for the quasilocal horizons and compare our results with Ashtekar-Kirshnan flux formula. The quasilocal energy-momentum and flux of generic isolated horizons and nonrotating dynamical horizons are discussed in this paper.

We present an analysis of the quark spectral function above and below the critical temperature for deconfinement performed at zero and nonzero momentum in quenched lattice QCD using clover improved Wilson fermions in Landau gauge. It is found that the temporal quark correlation function in the deconfined phase near the critical temperature is well reproduced by a two-pole ansatz for the spectral function. This indicates that excitation modes of the quark field have small decay rates. The bare quark mass and momentum dependence of the spectral function is analyzed with this ansatz. In the chiral limit we find that the quark spectral function has two collective modes corresponding to the normal and plasmino excitations in the high-temperature limit. Over a rather wide temperature range in the deconfined phase the pole mass of these modes at zero momentum, which corresponds to the thermal mass of the quark, is approximately proportional to temperature. With increasing bare quark masses the plasmino mode gradually disappears, and the spectral function is dominated by a single pole. We also discuss quasiparticle properties of heavy quarks in the deconfined phase. In the confined phase, it is found that the pole ansatz for the spectral function fails completely.

Scalar composite boson masses have been computed in QCD and technicolor theories with the help of the homogeneous Bethe-Salpeter equation, resulting in a scalar mass that is twice the dynamically generated fermion or technifermion mass ($m_{\mathrm{dyn}}$). We show that in the case of walking (or quasiconformal) technicolor theories, where the $m_{\mathrm{dyn}}$ behavior with the momenta may be quite different from the one predicted by the standard operator product expansion, this result is incomplete and we must consider the effect of the normalization condition of the Bethe-Salpeter equation to determine the scalar masses. We compute the composite Higgs boson mass for several groups with technifermions in the fundamental and higher dimensional representations and comment about the experimental constraints on these theories, which indicate that models based on walking theories with fermions in the fundamental representation may, within the limitations of our approach, have masses quite near the actual direct exclusion limit.

We examine whether the cosmic ray positron excess observed by PAMELA can be explained by neutralino annihilation in the next-to-minimal supersymmetric standard model (NMSSM). The main dark matter annihilation products are the lightest $CP$-even scalar $h_1$ plus the lightest $CP$-odd scalar $a_1$, with the $a_1$ decaying into two muons. The energetic positrons needed to explain PAMELA are thus obtained in the NMSSM simply from kinematics. The required large annihilation cross section is obtained from an $s$-channel resonance with the heavier $CP$-odd scalar $a_2$. Various experiments constrain the PAMELA-favored NMSSM parameter space, including collider searches for a light $a_1$. These constraints point to a unique corner of the NMSSM parameter space, having a lightest neutralino mass around 160 GeV and a very light pseudoscalar mass less than a GeV. A simple parametrized formula for the charge-dependent solar modulation effects reconciles the discrepancy between the PAMELA data and the estimated background at lower energies. We also discuss the electron and gamma-ray spectra from the Fermi LAT observations, and point out the discrepancy between the NMSSM predictions and Fermi LAT preliminary results and possible resolution. An NMSSM explanation of PAMELA makes three striking and uniquely correlated predictions: the rise in the PAMELA positron spectrum will turn over at around 70 GeV, the dark matter particle mass is less than the top quark mass, and a light sub-GeV pseudoscalar will be discovered at colliders.

We investigate the quark mass dependence of baryon masses in $2+1$ flavor lattice QCD using SU(3) heavy baryon chiral perturbation theory up to one-loop order. The baryon mass data used for the analyses are obtained for the degenerate up-down quark mass of 3 to 24 MeV and two choices of the strange quark mass around the physical value. We find that the SU(3) chiral expansion fails to describe both the octet and the decuplet baryon data if phenomenological values are employed for the meson-baryon couplings. The SU(2) case is also examined for the nucleon. We observe that higher order terms are controlled only around the physical point. We also evaluate finite size effects using SU(3) heavy baryon chiral perturbation theory, finding small values of order 1% even at the physical point.

We comment on the assertion made by Caselle et al. [M. Caselle, G. Delfino, P. Grinza, O. Jahn, and N. Magnoli, J. Stat. Mech. (2006) P008.] that the confining (string) potential for three quarks “makes a smooth crossover transition from the $\Delta$-string to the $Y$-string configuration at interquark distances of around 0.8 fm”. We study the functional dependence of the three-quark confining potentials due to a $Y$-string, and the $\Delta$ string and show that they have different symmetries, which lead to different constants of the motion (i.e. they belong to different “universality classes” in the parlance of the theory of phase transitions). This means that there is no “smooth crossover” between the two, when their string tensions are identical, except at the vanishing hyper-radius. We also comment on a certain two-body potential approximation to the $Y$-string potential.

Using data collected near the $D_s^{*\pm }{D}_s^{\mp }$ peak production energy $E_{\mathrm{cm}}=4170\mathrm{MeV}$ by the CLEO-c detector, we search for $D_s^{+}$ exclusive hadronic decays involving $\omega$. We find $\mathcal{B}(D_s^{+}\to {\pi }^{+}\omega )=(0.21\pm 0.09\pm 0.01)\%$, $\mathcal{B}(D_s^{+}\to {\pi }^{+}{\pi }^0\omega )=(2.78\pm 0.65\pm 0.25)\%$, $\mathcal{B}(D_s^{+}\to {\pi }^{+}{\pi }^{+}{\pi }^{-}\omega )=(1.58\pm 0.45\pm 0.09)\%$, $\mathcal{B}(D_s^{+}\to {\pi }^{+}\eta \omega )=(0.85\pm 0.54\pm 0.06)\%$, $\mathcal{B}(D_s^{+}\to K^{+}\omega )<0.24\%$, $\mathcal{B}(D_s^{+}\to K^{+}{\pi }^0\omega )<0.82\%$, $\mathcal{B}(D_s^{+}\to K^{+}{\pi }^{+}{\pi }^{-}\omega )<0.54\%$, and $\mathcal{B}(D_s^{+}\to K^{+}\eta \omega )<0.79\%$. The upper limits are at 90% confidence level.

The vacuum persistence can be written as the Bose-Einstein distribution in spinor QED and as the Fermi-Dirac distribution in scalar QED exactly in a constant electric field and approximately in time-dependent electric fields. The inverse temperature is determined by the period of charged particle in the Euclidean time and the negative chemical potential by the ratio of the worldline instanton to the inverse temperature. The negativity of chemical potential is due to the vacuum instability under strong electric fields. The inversion of spin statistics in the vacuum persistence is a consequence of the Bogoliubov relations for fermions and bosons.

We embed the loop quantum gravity Barbero-Immirzi parameter and field within an action describing 4D, $\mathcal{N}=1$ supergravity and thus within a low-energy effective action of superstring/M theory. We use the fully gauge-covariant description of supergravity in (curved) superspace. The gravitational constant is replaced with the vacuum expectation value of a scalar field, which in local supersymmetry is promoted to a complex, covariantly chiral scalar superfield. The imaginary part of this superfield couples to a supersymmetric Holst term. The Holst term also serves as a starting point in the loop quantum gravity action. This suggest the possibility of a relation between loop quantum gravity and supersymmetric string theory, where the Barbero-Immirzi parameter and field of the former play the role of the supersymmetric axion in the latter. Adding matter fermions in loop quantum gravity may require the extension of the Holst action through the Nieh-Yan topological invariant, while in pure, matter-free supergravity their supersymmetric extensions are the same. We show that, when the Barbero-Immirzi parameter is promoted to a field in the context of 4D supergravity, it is equivalent to adding a dynamical complex chiral (dilaton-axion) superfield with a nontrivial kinetic term (or Kähler potential), coupled to supergravity.

We reassess the method of the linear delta expansion for the calculation of effective potentials in superspace, by adopting the improved version of the super-Feynman rules in the framework of the O’Raifeartaigh model for spontaneous supersymmetry breaking. The effective potential is calculated using both the fastest apparent convergence and the principle of minimal sensitivity criteria and the consistency and efficacy of the method are checked in deriving the Coleman-Weinberg potential.

Chern-Simons modified gravity is a four-dimensional, effective theory that descends both from string theory and loop quantum gravity, and that corrects the Einstein-Hilbert action by adding the product of a scalar field and the parity-violating, Pontryagin density. The Chern-Simons modification deforms the gravitational field of spinning black holes, which is now described by a modified Kerr geometry whose multipole moments deviate from the Kerr ones only at the fourth multipole $\ell =4$. This paper investigates possible signatures of this theory in the gravitational-wave emission produced in the inspiral of stellar compact objects into massive black holes, both for intermediate- and extreme-mass ratios. We use the semirelativistic approximation, where the trajectory of the small compact object is modeled via geodesics of the massive black hole geometry, while the gravitational waveforms are obtained from a multipolar decomposition of the radiative field. The main Chern-Simons corrections to the waveforms arise from modifications to the geodesic trajectories, which in turn are due to changes to the massive black hole geometry, and manifest themselves as an accumulating dephasing relative to the general relativistic case. We also explore the propagation and the stress-energy tensor of gravitational waves in this theory, using the short-wavelength approximation. We find that, although this tensor has the same form as in general relativity, the energy and angular momentum balance laws are indeed modified through the stress-energy tensor of the Chern-Simons scalar field. These balance laws could be used to describe the inspiral through adiabatic changes in the orbital parameters, which in turn would enhance the dephasing effect. Gravitational-wave observations of intermediate- or extreme-mass-ratio inspirals with advanced ground detectors or with the Laser Interferometer Space Antenna could use such dephasing to test the dynamical theory to unprecedented levels, thus beginning the era of gravitational-wave tests of effective quantum gravity theories.

Using the covariant formalism, we derive the equations of motion for adiabatic and entropy perturbations at third order in perturbation theory for cosmological models involving two scalar fields. We use these equations to calculate the trispectrum of ekpyrotic and cyclic models in which the density perturbations are generated via the entropic mechanism. In these models, the conversion of entropy into curvature perturbations occurs just before the big bang, either during the ekpyrotic phase or during the subsequent kinetic energy dominated phase. In both cases, we find that the nonlinearity parameters $f_{\mathrm{NL}}$ and $g_{\mathrm{NL}}$ combine to leave a very distinct observational imprint.

We study analytically and numerically the bounds imposed by the electroweak precision tests on a minimal composite Higgs model. The model is based on spontaneous $SO(5)\to SO(4)$ breaking, so that an approximate custodial symmetry is preserved. The Higgs arises as a pseudo-Goldstone boson at a scale below the electroweak symmetry breaking scale. We show that one can satisfy the electroweak precision constraints without much fine-tuning. This is the case if the left-handed top quark is fully composite, which gives a mass spectrum within the reach of the LHC. However a composite top quark is strongly disfavored by flavor physics. The alternative is to have a singlet top partner at a scale much lighter than the rest of the composite fermions. In this case the top partner would be light enough to be produced significantly at the LHC.

It is known that a classical $SU(2)$ Einstein-Yang-Mills theory in $3+1$ dimensional anti–de Sitter spacetime can provide a holographic dual to a $2+1$ dimensional time reversal symmetry breaking superconductor with a pseudogap. We study the properties of this holographic superconductor in the presence of an applied constant external magnetic field, neglecting backreaction on the geometry. The superconductor is immersed into a constant external magnetic field by adding a radially (the extra dimension) dependent magnetic field to the black hole. As for real superconductors, there is a critical magnetic field above which no superconductivity can appear. The continuity of the first derivative of the free energy difference between the superconducting phase and the normal phase at the critical temperature suggests that the superconducting phase transition with applied magnetic field is of second order.