Commutative four dimensional supersymmetric Yang-Mills (SYM) theory is known to be renormalizable for $\mathcal{N}=1,2$, and finite for $\mathcal{N}=4$. However, in the noncommutative version of the model the UV/IR mechanism gives rise to infrared divergences which may spoil the perturbative expansion. In this work we pursue the study of the consistency of the $\mathcal{N}=1,2,4$ noncommutative supersymmetric Yang-Mills theory with gauge group $\mathrm{U}(N)$ (NCSYM). We employ the covariant superfield framework to compute the one-loop corrections to the two- and three-point functions of the gauge superfield $V$. It is found that the cancellation of the harmful UV/IR infrared divergences only takes place in the fundamental representation of the gauge group. We argue that this is in agreement with the low energy limit of the open superstring in the presence of an external magnetic field. As expected, the planar sector of the two-point function of the $V$ superfield exhibits UV divergences. They are found to cancel, in the Feynman gauge, for the maximally extended $\mathcal{N}=4$ supersymmetric theory. This gives support to the belief that the $\mathcal{N}=4$ NCSYM theory is UV finite.

We consider the neutral pion and nucleon fields interacting via the pseudoscalar (PS) Yukawa-type coupling. The method of unitary clothing transformations is used to handle the so-called clothed particle representation, where the total field Hamiltonian and the three boost operators in the instant form of relativistic dynamics take on the same sparse structure in the Hilbert space of hadronic states. In this approach the mass counterterms are cancelled (at least, partly) by commutators of the generators of clothing transformations and the field interaction operator. This allows the pion and nucleon mass shifts to be expressed through the corresponding three-dimensional integrals whose integrands depend on certain covariant combinations of the relevant three-momenta. The property provides the momentum independence of mass renormalization. The present results prove to be equivalent to the results obtained by Feynman techniques.

We present full numerical solutions to the system of a global string embedded in a six-dimensional space-time. The solutions are regular everywhere and do confine gravity in our four-dimensional world. They depend on the value of the (negative) cosmological constant in the bulk and on the parameters of the Higgs potential, and we perform a systematic study to determine their allowed values. We also comment on the relation of our results with previous studies on the same subject and on their phenomenological viability.

We reinvestigate the thermodynamics of black objects (holes and strings) in four-dimensional braneworld models that are originally constructed by Emparan, Horowitz and Myers based on the anti- de Sitter (AdS) C-metric. After proving the uniqueness of slicing the AdS C-metric, we derive thermodynamic quantities of the black objects by means of the Euclidean formulation and find that we have no necessity of requiring any regularization to calculate their classical action. We show that there exist the Bekenstein-Hawking law and the thermodynamic first law. The thermodynamic mass of the localized black hole on a flat brane is negative, and it differs from the one previously derived. We discuss the thermodynamic stabilities and show that the Banãdos-Teitelboim-Zanelli (BTZ) black string is more stable than the localized black holes in a canonical ensemble, except for an extreme case. We also find a braneworld analogue of the Hawking-Page transition between the BTZ black string and thermal AdS branes. The localized black holes on a de Sitter brane is discussed by considering Nariai instanton, comparing the study of “black cigar” in the five-dimensional braneworld model.

At present no theory of a massive graviton is known that is consistent with experiments at both long and short distances. The problem is that consistency with long distance experiments requires the graviton mass to be very small. Such a small graviton mass however implies an ultraviolet cutoff for the theory at length scales far larger than the millimeter scale at which gravity has already been measured. In this paper we attempt to construct a model which avoids this problem. We consider a brane world setup in warped anti- de Sitter spacetime and we investigate the consequences of writing a mass term for the graviton on an infrared brane where the local cutoff is of order a large (galactic) distance scale. The advantage of this setup is that the low cutoff for physics on the infrared brane does not significantly affect the predictivity of the theory for observers localized on the ultraviolet brane. For such observers the predictions of this theory agree with general relativity at distances smaller than the infrared scale but go over to those of a theory of massive gravity at longer distances. A careful analysis of the graviton two-point function, however, reveals the presence of a ghost in the low energy spectrum. A mode decomposition of the higher dimensional theory reveals that the ghost corresponds to the radion field. We also investigate the theory with a brane-localized mass for the graviton on the ultraviolet brane, and show that the physics of this case is similar to that of a conventional four dimensional theory with a massive graviton, but with one important difference: when the infrared brane decouples and the would-be massive graviton gets heavier than the regular Kaluza-Klein modes, it becomes unstable and it has a finite width to decay off the brane into the continuum of Kaluza-Klein states.

It was recently shown by Whinnett and Torres [A. W. Whinnett and D. F. Torres, Astrophys. J. 603, L133 (2004).] that the phenomenon of spontaneous scalarization in compact objects (polytropes) was accompanied also by a spontaneous violation of the weak energy condition (WEC). Notably, by the encounter of negative-energy densities as measured by a static observer at several points of the star. Here we argue that such a situation is not generic of scalar-tensor theories of gravity (STT). We support this conclusion by numerical results within a class of STT and by using three realistic models of dense matter. However, we show that the “angular parts” of the additional conditions needed for the WEC to hold ${\rho }_{\mathrm{e}\mathrm{f}\mathrm{f}}+T_i^{i(\mathrm{e}\mathrm{f}\mathrm{f})}\ge 0$ tend to be “slightly violated” at the outskirts of the star.

It is conjectured that inflation, taking account of quantum gravity, leads to a discrete spectrum of cosmological perturbations, instead of the continuous Gaussian spectrum predicted by standard field theory in an unquantized background. Heuristic models of discrete spectra are discussed, based on an inflaton mode with self-gravity, a lattice of amplitude states, an entangled ensemble of modes, and the holographic or covariant entropy bound. Estimates are given for the discreteness observable in cosmic background anisotropy, galaxy clustering, and gravitational wave backgrounds.

We analyze the evolution of light Q-balls in a cosmological background, and find a number of interesting features. For Q-balls formed with a size comparable to the Hubble radius, we demonstrate that there is no charge radiation, and that the Q-ball maintains a constant physical radius. Large expansion rates cause charge migration to the surface of the Q-ball, corresponding to a nonhomogeneous internal rotation frequency. We argue that this is an important phenomenon as it leads to a large surface charge and possible fragmentation of the Q-ball. We also explore the deviation of the Q-ball profile function from the static case. By introducing a parameter $ϵ$, which is the ratio of the Hubble parameter to the frequency of oscillation of the Q-ball field, and using solutions to an analytically approximated equation for the profile function, we determine the dependence of the new features on the expansion rate. This allows us to gain an understanding of when they should be considered and when they can be neglected, thereby placing restrictions on the existence of homogeneous Q-balls in expanding backgrounds.

We consider the generalized Chaplygin gas (GCG) proposal for unification of dark energy and dark matter and show that it admits an unique decomposition into dark energy and dark matter components once phantomlike dark energy is excluded. Within this framework, we study structure formation and show that difficulties associated to unphysical oscillations or blowup in the matter power spectrum can be circumvented. Furthermore, we show that the dominance of dark energy is related to the time when energy density fluctuations start deviating from the linear $\delta \sim a$ behavior.

After the precise observations of the cosmic microwave background (CMB) anisotropy power spectrum, attention is now being focused on higher order statistics of the CMB anisotropies. Since linear evolution preserves the statistical properties of the initial conditions, observed non-Gaussianity of the CMB will mirror primordial non-Gaussianity. Single-field slow-roll inflation robustly predicts negligible non-Gaussianity so an indication of primordial non-Gaussianity will suggest alternative scenarios need to be considered. In this paper we calculate the information on primordial non-Gaussianity encoded in the polarization of the CMB. After deriving the optimal weights for a cubic estimator we evaluate the signal-to-noise ratio $(S/N)$ of the estimator for Wilkinson Microwave Anisotropy Probe, Planck, and an ideal cosmic variance limited experiment. We find that when the experiment can observe CMB polarization with good sensitivity, the sensitivity to primordial non-Gaussianity increases by roughly a factor of 2. We also test the weakly non-Gaussian assumption used to derive the optimal weight factor by calculating the degradation factor produced by the gravitational lensing induced connected four-point function. The physical scales in the radiative transfer functions are largely irrelevant for the constraints on the primordial non-Gaussianity. We show that the total $(S/N{)}^2$ is simply proportional to the number of observed pixels on the sky.

The Laser Interferometer Space Antenna (LISA) is expected to provide the largest observational sample of binary systems of faint subsolar mass compact objects, in particular, white-dwarfs, whose radiation is monochromatic over most of the LISA observational window. Current astrophysical estimates suggest that the instrument will be able to resolve $\sim {10}^4$ such systems, with a large fraction of them at frequencies $\gtrsim 3\mathrm{m}\mathrm{H}\mathrm{z}$, where the wavelength of gravitational waves becomes comparable to or shorter than the LISA armlength. This affects the structure of the so-called LISA transfer function which cannot be treated as constant in this frequency range: it introduces characteristic phase and amplitude modulations that depend on the source location in the sky and the emission frequency. Here we investigate the effect of the LISA transfer function on detection and parameter estimation for monochromatic sources. For signal detection we show that filters constructed by approximating the transfer function as a constant (long-wavelength approximation) introduce a negligible loss of signal-to-noise ratio—the fitting factor always exceeds 0.97—for $f\le 10\mathrm{m}\mathrm{H}\mathrm{z}$, therefore in a frequency range where one would actually expect the approximation to fail. For parameter estimation, we conclude that in the range $3\mathrm{m}\mathrm{H}\mathrm{z}\lesssim f\lesssim 30\mathrm{m}\mathrm{H}\mathrm{z}$ the errors associated with parameter measurements differ from $\simeq 5\%$ up to a factor $\sim 10$ (depending on the actual source parameters and emission frequency) with respect to those computed using the long-wavelength approximation.

Linearized gravitational waves in Brans-Dicke and scalar-tensor theories carry negative energy. A gauge-invariant analysis shows that the background Minkowski space is stable at the classical level with respect to linear scalar and tensor inhomogeneous perturbations.

Rare nonleptonic ${\Omega }^{-}\to {\Xi }^0(1530){\pi }^{-}$ decay branching ratio is estimated by means of the QCD enhanced effective weak Hamiltonian supplemented by the $\mathrm{S}\mathrm{U}(3)$ Skyrme model used to estimate the nonperturbative matrix elements. Using mean values for experimental input parameters and the Skyrme charge $e=4.75$ we obtain the rate which is in good agreement with data.

$K_S^0{K}_L^0$ from ${\psi }^{\prime \prime }$ decays is searched for using the ${\psi }^{\prime \prime }$ data collected by BESII at BEPC, and the upper limit of the branching fraction is determined to be $\mathcal{B}({\psi }^{\prime \prime }\to K_S^0{K}_L^0)<2.1\times {10}^{-4}$ at 90% C.L. The measurement is compared with the prediction of the $S$- and $D$-wave mixing model of the charmonia, based on the measurements of the branching fractions of $J/\psi \to K_S^0{K}_L^0$ and ${\psi }^{\prime }\to K_S^0{K}_L^0$.

We study four flavor QCD at nonzero temperature and density by analytic continuation from an imaginary chemical potential. The explored region is $T=0.95T_c<T<3.5T_c$, and the baryochemical potentials range from 0 to $\simeq 500\mathrm{M}\mathrm{e}\mathrm{V}$. Observables include the number density, the order parameter for chiral symmetry, and the pressure, which is calculated via an integral method at fixed temperature and quark mass. The simulations are carried out on a ${16}^3\times 4$ lattice, and the mass dependence of the results is estimated by exploiting the Maxwell relations. In the hadronic region, we confirm that the results are consistent with a simple resonance hadron gas model, and we estimate the critical density by combining the results for the number density with those for the critical line. In the hot phase, above the end point of the Roberge-Weiss transition $T_E\simeq 1.1T_c$, the results are consistent with a free lattice model with a fixed effective number of flavor slightly different from four. We confirm that confinement and chiral symmetry are coincident by a further analysis of the critical line, and we discuss the interrelation between thermodynamics and critical behavior. We comment on the strength and weakness of the method, and propose further developments.

We consider constraints on the momentum fraction of the $K$ and $K^{*}$ meson carried by the strange quark that follow from exact operator identities, similar to those for the divergence of the quark part of the QCD energy-momentum tensor. The existing QCD sum rule estimates are reanalyzed in this context. Our conclusions essentially support the constituent quark-model picture where the momentum fraction is roughly proportional to the constituent quark mass, but the asymmetry turns out to be smaller compared to the naive quark-model estimates. As a by-product of this study, we calculate the SU(3)-breaking quark-antiquark-gluon matrix elements that determine the leading conformal spin contributions to the asymmetry in twist-four distribution amplitudes of strange mesons $K$ and $K^{*}$, and also update the estimate for the SU(3) breaking for the quark-antiquark-gluon vacuum condensate.

We study the structure of generalized parton distributions in impact parameter space with the aim of determining the size and the role of small transverse separation components in the quark wave function. We analyze the relation between transverse momentum components and transverse separations. Wave functions with large transverse momentum components can simultaneously reproduce the behavior of the Dirac form factor at large momentum transfer and of the deep inelastic structure functions at Bjorken $x\to 1$. The presence of large momentum components does not ensure, however, the dominance of small transverse distances at large $x$. We suggest that experiments measuring the attenuation of hadrons in the nuclear medium, or the onset of color transparency, can provide an alternative source of information on generalized parton distributions by mapping out the behavior of the transverse components of the wave function.

We consider the effects of quantum anomalies involving the baryon current for high-density matter. In the effective Lagrangian, the anomaly terms describe the interaction of three light fields: the electromagnetic photons $A_{\mu }$, neutral light Nambu-Goldstone bosons ($\pi$, $\eta$, ${\eta }^{\prime }$), and the superfluid phonon. The anomaly induced interactions lead to a number of interesting phenomena which may have phenomenological consequences observable in neutron stars.

The weak boson fusion process for neutral Higgs boson production is investigated with particular attention to the accuracy with which the Higgs boson coupling to weak bosons can be determined at CERN Large Hadron Collider energies in final states that contain a Higgs boson plus at least two jets. Using fully differential perturbative matrix elements for the weak boson fusion signal process and for the QCD background processes, we generate events in which a Higgs boson is produced along with two jets that carry large transverse momentum. The effectiveness of different prescriptions to enhance the signal-to background ratio is studied, and the expected signal purities are calculated in each case. We find that a simple cut on the rapidity of one final-state jet works well. We determine that an accuracy of $\delta g/g\sim 10\%$ on the effective coupling $g$ may be possible after $\sim 200{\mathrm{f}\mathrm{b}}^{-1}$ of integrated luminosity is accumulated at the Large Hadron Collider.