A large symmetry group is perhaps experimentally observed in excited hadrons which includes the chiral group $U(2{)}_L\times U(2{)}_R$ as a subgroup. To possess this large symmetry a dynamical model for excited hadrons, presumably a string model, should explain formation of chiral multiplets and, at the same time, predict coinciding slopes of the angular and radial Regge trajectories. This is possible only if both the dynamics of the string and the chirality of the quarks at the ends of the string are considered together. We construct a model-independent unitary transformation from the relativistic chiral basis to the $\{{}^{2S+1}L_J\}$ basis, commonly used in hadronic phenomenology as well as in the string models, and demonstrate that a hadron belonging to the given chiral representation is a fixed superposition of the basis vectors with different $L$’s. Thus the description of highly excited hadron in terms of a fixed $L$ is not compatible with chiral symmetry and has to be disregarded in favor of the description in terms of the total hadron spin $J$. Therefore, dynamics of the string must deliver the principal quantum number $\sim n+J$, in order chiral multiplets with different spins to become degenerate, as required by the large symmetry group.

Top-squark-mediated annihilation of $b$-ino-like neutralinos to top-antitop pairs can play the dominant role in obtaining a thermal relic dark matter abundance in agreement with observations. In a previous paper, it was argued that this can occur naturally in models of compressed supersymmetry, which feature a running gluino mass parameter that is substantially smaller than the $W$-ino mass parameter at the scale of apparent gauge coupling unification. Here I study in some more detail the parameter space in which this is viable, and compare to other scenarios for obtaining the observed dark matter density. I then study the possibility of detecting the dark matter directly in future experiments. The prospects are consistently very promising for a wide variety of model parameters within this scenario.

We interpret the current experimental limit on the lightest Higgs boson mass to suggest that, if nature is supersymmetric, there are additional interactions beyond those of the minimal supersymmetric standard model (MSSM) coming from new degrees of freedom around the TeV scale. Within an effective field theory analysis, the leading order corrections to the MSSM are described in terms of only two operators. This provides a highly constrained description of beyond MSSM physics. The scalar Higgs spectrum as well as the chargino and neutralino spectra and couplings are modified in a distinctive way. These operators can be generated by a variety of microscopic mechanisms.

We compare several recent theoretical studies of the single transverse-spin asymmetry in dijet correlations at hadron colliders. We show that the results of these studies are all consistent. To establish this, we investigate, in particular, the two-gluon exchange contributions to the relevant initial and final-state interactions in the context of a simplifying model. Overall, the results confirm that the dijet imbalance obeys, at best, a nonstandard or “generalized” transverse-momentum-dependent factorization.

We construct a sigma model in two dimensions with Galilean symmetry in flat target space similar to the sigma model of the critical string theory with Lorentz symmetry in 10 flat spacetime dimensions. This is motivated by the works of Gomis and Ooguri [J. Math. Phys. (N.Y.) 42, 3127 (2001)] and Danielsson et al. [J. High Energy Phys. 10 (2000) 020; J. High Energy Phys. 03 (2001) 041.]. Our theory is much simpler than their theory and does not assume a compact coordinate. This nonrelativistic string theory has a bosonic matter $\beta \gamma$ conformal field theory with the conformal weight of $\beta$ as 1. It is natural to identify time as a linear combination of $\gamma$ and $\overline{\gamma }$ through an explicit realization of the Galilean boost symmetry. The angle between $\gamma$ and $\overline{\gamma }$ parametrizes one parameter family of selection sectors. These selection sectors are responsible for having a nonrelativistic dispersion relation without a nontrivial topology in the nonrelativistic setup, which is one of the major differences from the previous works of Gomis and Ooguri and of Danielsson and co-workers. This simple theory is the nonrelativistic analogue of the critical string theory, and there are many different avenues ahead to be investigated. We mention a possible consistent generalization of this theory with different conformal weights for the $\beta \gamma$ conformal field theory. We also mention supersymmetric generalizations of these theories.

A general class of nonlocal cosmological models is considered. A new method for solving nonlocal Friedmann equations is proposed, and solutions of the Friedmann equations with nonlocal operator are presented. The cosmological properties of these solutions are discussed. Especially indicated is the $p$-adic cosmological model in which we have obtained a nonsingular bouncing solution and string field theory tachyon model in which we have obtained full solution of nonlocal Friedmann equations with $w=-1$ at large times. The possibility of obtaining a realistic value of the cosmological constant from nonlocal cosmological models is also discussed.

We present new soliton and hairy black hole solutions of $\mathfrak{s}\mathfrak{u}(N)$ Einstein-Yang-Mills theory in asymptotically anti-de Sitter space. These solutions are described by $N+1$ independent parameters, and have $N-1$ gauge field degrees of freedom. We examine the space of solutions in detail for $\mathfrak{s}\mathfrak{u}(3)$ and $\mathfrak{s}\mathfrak{u}(4)$ solitons and black holes. If the magnitude of the cosmological constant is sufficiently large, we find solutions where all the gauge field functions have no zeros. These solutions are of particular interest because we anticipate that at least some of them will be linearly stable.

It is generally believed that the angular resolution of the Laser Interferometer Space Antenna (LISA) for binary supermassive black holes (SMBH) will not be good enough to identify the host galaxy or galaxy cluster. This conclusion, based on using only the dominant harmonic of the binary SMBH signal, changes substantially when higher signal harmonics are included in assessing the parameter estimation problem. We show that in a subset of the source parameter space the angular resolution increases by more than a factor of 10, thereby making it possible for LISA to identify the host galaxy/galaxy cluster. Thus, LISA’s observation of certain binary SMBH coalescence events could constrain the dark energy equation of state to within a few percent, comparable to the level expected from other dark energy missions.

We present a new numerical code developed for the evolution of binary black-hole spacetimes using different initial data and evolution techniques. The code is demonstrated to produce state-of-the-art simulations of orbiting and inspiralling black-hole binaries with convergent waveforms. We also present the first detailed study of the dependence of gravitational waveforms resulting from three-dimensional evolutions of different types of initial data. For this purpose we compare the waveforms generated by head-on collisions of superposed Kerr-Schild, Misner, and Brill-Lindquist data over a wide range of initial separations.

We consider a two-brane system in five-dimensional anti–de Sitter space-time. We study particle creation due to the motion of the physical brane which first approaches the second static brane (contraction) and then recedes from it (expansion). The spectrum and the energy density of the generated gravitons are calculated. We show that the massless gravitons have a blue spectrum and that their energy density satisfies the nucleosynthesis bound with very mild constraints on the parameters. We also show that the Kaluza-Klein modes cannot provide the dark matter in an anti–de Sitter braneworld. However, for natural choices of parameters, backreaction from the Kaluza-Klein gravitons may well become important. The main findings of this work have been published in the form of a Letter [R. Durrer and M. Ruser, Phys. Rev. Lett. 99, 071601 (2007)].

We study the emission of fermion and gauge boson degrees of freedom on the brane by a rotating higher-dimensional black hole. Using matching techniques, for the near-horizon and far-field regime solutions, we solve analytically the corresponding field equations of motion. From this, we derive analytical results for the absorption probabilities and Hawking radiation emission rates, in the low-energy and low-rotation case, for both species of fields. We produce plots of these, comparing them to existing exact numerical results with very good agreement. We also study the total absorption cross section and demonstrate that, as in the nonrotating case, it has a different behavior for fermions and gauge bosons in the low-energy limit, while it follows a universal behavior—reaching a constant, spin-independent, asymptotic value—in the high-energy regime.

Some components of the graviton two-point function have been recently computed in the context of loop quantum gravity, using the spinfoam Barrett-Crane vertex. We complete the calculation of the remaining components. We find that, under our assumptions, the Barrett-Crane vertex does not yield the correct long-distance limit. We argue that the problem is general and can be traced to the intertwiner independence of the Barrett-Crane vertex, and therefore to the well-known mismatch between the Barrett-Crane formalism and the standard canonical spin networks. In another paper we illustrate the asymptotic behavior of a vertex amplitude that can correct this difficulty.

A characteristic of D-brane inflation is that fluctuations in the inflaton field can propagate at a speed significantly less than the speed of light. This yields observable effects that are distinct from those of single-field slow-roll inflation, such as a modification of the inflationary consistency relation and a potentially large level of non-Gaussianities. We present a numerical algorithm that extends the inflationary flow formalism to models with general speed of sound. For an ensemble of D-brane-inflation models parametrized by the Hubble parameter and the speed of sound as polynomial functions of the inflaton field, we give qualitative predictions for the key inflationary observables. We discuss various consistency relations for D-brane inflation, and compare the qualitative shapes of the warp factors we derive from the numerical models with analytical warp factors considered in the literature. Finally, we derive and apply a generalized microphysical bound on the inflaton field variation during brane inflation. While a large number of models are consistent with current cosmological constraints, almost all of these models violate the compactification constraint on the field range in four-dimensional Planck units. If the field range bound is to hold, then models with a detectable level of non-Gaussianity predict a blue scalar spectral index, and a tensor component that is far below the detection limit of any future experiment.

We propose a simple quantum field theoretical toy model for black-hole evaporation and study the backreaction of Hawking radiation onto the classical background. It turns out that the horizon is also “pushed back” in this situation (i.e., the interior region shrinks) though this backreaction is not caused by energy conservation but by momentum balance. The effective heat capacity and induced entropy variation can have both signs—depending on the parameters of the model.

The Lorentzian spacetime metric is refined to an area metric which naturally emerges as a generalized geometry in quantum string and gauge theory. Employing the area metric curvature scalar, the Einstein-Hilbert gravitational action is reinterpreted as dynamics for an area metric. The area metric cosmology of the radiation-dominated early universe does not depart from general relativity, enabling successful nucleosynthesis. But intriguingly, without the need for dark energy or fine-tuning, area metric cosmology explains the observed small acceleration of the late universe.

We study a three dimensional Z(3)-symmetric effective theory of high temperature QCD. The exact lattice-continuum relations needed in order to perform lattice simulations with physical parameters are computed to order $\mathcal{O}(a^0)$ in lattice perturbation theory. Lattice simulations are performed to determine the phase structure of a subset of the parameter space.

We present a lattice QCD calculation of the $\rho$ meson decay width via the $P$-wave scattering phase shift for the $I=1$ two-pion system. Our calculation uses full QCD gauge configurations for $N_f=2$ flavors generated using a renormalization group improved gauge action and an improved Wilson fermion action on a ${12}^3\times 24$ lattice at $m_{\pi }/m_{\rho }=0.41$ and the lattice spacing $1/a=0.92\mathrm{GeV}$. The phase shift calculated with the use of the finite size formula for the two-pion system in the moving frame shows a behavior consistent with the existence of a resonance at a mass close to the vector meson mass obtained in spectroscopy. The decay width estimated from the phase shift is consistent with the experiment, when the quark mass is scaled to the realistic value.

The Landau-gauge gluon propagator is studied using the coarse and fine dynamical MILC configurations. The effects of dynamical quarks are clearly visible and lead to a reduction of the nonperturbative infrared enhancement relative to the quenched case. Lattice spacing effects are studied and found to be small. The gluon spectral function is shown to clearly violate positivity in both quenched and full QCD.

Many new physics models predict resonances with masses in the TeV range which decay into a pair of top quarks. With its large cross section, $t\overline{t}$ production at the Large Hadron Collider (LHC) offers an excellent opportunity to search for such particles. The identification of very energetic top quarks is crucial in such an analysis. We consider in detail the $t\overline{t}\to {\ell }^{\pm }\nu b\overline{b}q{\overline{q}}^{\prime }$ ($\ell =e,\mu$) final state for high $p_T$ top quarks. In this phase space region, two or more of the final state quarks can merge into a single jet due to the large Lorentz boost of the parent top quark. As a result, a large fraction of $t\overline{t}\to {\ell }^{\pm }\nu b\overline{b}q{\overline{q}}^{\prime }$ events with an invariant mass in the TeV region contains less than four observable jets. Requiring one or two tagged $b$-quarks, we calculate the $W+\mathrm{\text{jets}}$, $Wb+\mathrm{\text{jets}}$, $Wb\overline{b}+\mathrm{\text{jets}}$, $Wbt$, and single top plus jets backgrounds for these final states, and identify cuts which help to suppress them. In particular, we discuss whether a cut on the jet invariant mass may be useful in reducing the background in the $\ell \nu +2\mathrm{\text{jets}}$ channel. We also investigate how next-to-leading-order QCD corrections affect high $p_T$ top quark production at the LHC. We find that the $\ell \nu +2\mathrm{\text{jets}}$ and $\ell \nu +3\mathrm{\text{jets}}$ final states with one or two $b$-tags will significantly improve the chances for discovering new heavy particles in the $t\overline{t}$ channel at the LHC.

Scattering and production amplitudes involving scalar resonances are known, according to Watson’s theorem, to share the same phase $\delta (s)$. We show that, at low energies, the production amplitude is fully determined by the combination of $\delta (s)$ with another phase $\omega (s)$, which describes intermediate two-meson propagation and is theoretically unambiguous. Our main result is a simple and almost model independent expression, which generalizes the usual $K$-matrix unitarization procedure and is suited to be used in analyses of production data involving scalar resonances.