Inclusive cross sections for $J/\psi$ production in proton-proton collisions were calculated in the $k_t$-factorization approach for the Relativistic Heavy Ion Collider (RHIC) energy. Several mechanisms were considered, including direct color-singlet mechanism, radiative decays of ${\chi }_c$ mesons, decays of ${\psi }^{\prime }$, open-charm-associated production of $J/\psi$ as well as weak decays of $B$ mesons. Different unintegrated gluon distributions from the literature were used. We find that radiative ${\chi }_c$ decays and direct color-singlet contributions constitute the dominant mechanism of $J/\psi$ production. These processes cannot be consistently treated within a collinear-factorization approach. The results are compared with recent RHIC data. The new precise data at small transverse momenta impose stringent constraints on unintegrated gluon distribution functions (UGDFs). Some UGDFs are inconsistent with the new data. The Kwieciński UGDFs give the best description of the data. In order to verify the mechanism suggested here we propose $J/\psi$–jet correlation measurement and an independent measurement of ${\chi }_c$ meson production in ${\pi }^{+}{\pi }^{-}$ and/or $K^{+}{K}^{-}$ decay channels. Finally, we address the issue of $J/\psi$ spin alignment.

We study the spacetime decay to nothing in string theory and M-theory. First we recall a nonsupersymmetric version of heterotic M-theory, in which bubbles of nothing—connecting the two $E_8$ boundaries by a throat—are expected to be nucleated. We argue that the fate of this system should be addressed at weak string coupling, where the nonperturbative instanton instability is expected to turn into a perturbative tachyonic one. We identify the unique string theory that could describe this process: The heterotic model with one $E_8$ gauge group and a singlet tachyon. We then use world sheet methods to study the tachyon condensation in the Neveu-Schwarz-Ramond formulation of this model, and show that it induces a world sheet super-Higgs effect. The main theme of our analysis is the possibility of making meaningful alternative gauge choices for world sheet supersymmetry, in place of the conventional superconformal gauge. We show in a version of unitary gauge how the world sheet gravitino assimilates the Goldstino and becomes dynamical. This picture clarifies recent results of Hellerman and Swanson. We also present analogs of $R_{\xi }$ gauges, and note the importance of logarithmic conformal field theories in the context of tachyon condensation.

In looking for imprints of extra dimensions in braneworld models one usually builds these so that they are compatible with known low energy physics and thus focuses on high energy effects. Nevertheless, just as submillimeter Newton’s law tests probe the mode structure of gravity other low energy tests might apply to matter. As a model example, in this work we determine the 4D Casimir force corresponding to a scalar field subject to Dirichlet boundary conditions on two parallel planes lying within the single brane of a Randall-Sundrum scenario extended by one compact extra dimension. Using the Green’s function method such a force picks the contribution of each field mode as if it acted individually but with a weight given by the square of the mode wave functions on the brane. In the low energy regime one regains the standard 4D Casimir force that is associated to a zero mode in the massless case or to a quasilocalized or resonant mode in the massive one while the effect of the extra dimensions gets encoded as an additional term.

We present the first $2+1$ flavor lattice QCD calculations of pseudoscalar flavor-singlet propagators using improved staggered fermions. We explore the relevant techniques and discuss prospects for the larger scale studies now in progress. The disconnected correlator is shown to have a highly non-Gaussian distribution and reliable estimates of the errors require care.

An energy correction is calculated in the time-independent perturbation setup using a regularized ultraviolet finite Hamiltonian on the noncommutative Minkowski space. The correction to the energy is invariant under rotation and translation but is not Lorentz covariant, and this leads to a distortion of the dispersion relation. In the limit where the noncommutativity vanishes, the common quantum field theory on the commutative Minkowski space is reobtained. The calculations are restricted to the regularized cubic interaction.

The relativistic accretion rate of dark matter by a black hole is revisited. Under the assumption that the phase space density indicator, $Q={\rho }_{\infty }/{\sigma }_{\infty }^3$, remains constant during the inflow, the derived accretion rate can be higher up to 5 orders of magnitude than the classical accretion formula, valid for nonrelativistic and noninteracting particles, when typical dark halo conditions are considered. For these typical conditions, the critical point of the flow is located at distances of about 30–150 times the horizon radius. Application of our results to black hole seeds hosted by halos issued from cosmological simulations indicate that dark matter contributes to no more than $\sim 10\%$ of the total accreted mass, confirming that the bolometric quasar luminosity is related to the baryonic accretion history of the black hole.

Extreme-mass-ratio inspirals (EMRIs) and intermediate-mass-ratio inspirals (IMRIs)—binaries in which a stellar-mass object spirals into a massive black hole or other massive, compact body—are important sources of gravitational waves for LISA and LIGO, respectively. Thorne has speculated that the waves from EMRIs and IMRIs encode, in principle, all the details of (i) the central body’s spacetime geometry (metric), (ii) the tidal coupling (energy and angular momentum exchange) between the central body and orbiting object, and (iii) the evolving orbital elements. Fintan Ryan has given a first partial proof that this speculation is correct: Restricting himself to nearly circular, nearly equatorial orbits and ignoring tidal coupling, Ryan proved that the central body’s metric is encoded in the waves. In this paper we generalize Ryan’s theorem. Retaining Ryan’s restriction to nearly circular and nearly equatorial orbits, and dropping the assumption of no tidal coupling, we prove that Thorne’s conjecture is nearly fully correct: the waves encode not only the central body’s metric but also the evolving orbital elements and (in a sense slightly different from Thorne’s conjecture) the evolving tidal coupling.

In a recent publication we developed a canonical quantization program describing the gravitational collapse of a spherical dust cloud in $2+1$ dimensions with a negative cosmological constant $-\Lambda \equiv -l^{-2}<0$. In this paper we address the quantization of the Banados-Teitelboim-Zanelli (BTZ) black hole. We show that the mass function describing the black hole is made of two pieces, a constant nonvanishing boundary contribution and a discrete spectrum of the form ${\mu }_n=\frac{\hslash }{l}(n+\frac{1}{2})$. The discrete spectrum is obtained by applying the Wheeler-DeWitt equation with a particular choice of factor ordering and interpreted as giving the energy levels of the collapsed matter shells that form the black hole. Treating a black hole microstate as a particular distribution of shells among the levels, we determine the canonical entropy of the BTZ black hole. Comparison with the Bekenstein-Hawking entropy shows that the boundary energy is related to the central charge of the Virasoro algebra that generates the asymptotic symmetry group of the three-dimensional anti-de Sitter space ${\mathrm{AdS}}_3$. This gives a connection between the Wheeler-DeWitt approach and the conformal field theory approach.

We study the formation of three-string junctions between $(p,q)$-cosmic superstrings, and collisions between such strings and show that kinematic constraints analogous to those found previously for collisions of Nambu-Goto strings apply here too, with suitable modifications to take account of the additional requirements of flux conservation. We examine in detail several examples involving collisions between strings with low values of $p$ and $q$, and also examine the rates of growth or shrinkage of strings at a junction. Finally, we briefly discuss the formation of junctions for strings in a warped space, specifically with a Klebanov-Strassler throat, and show that similar constraints still apply with changes to the parameters taking account of the warping and the background flux.

The causal entropic principle has been proposed as an alternative to the anthropic principle for understanding the magnitude of the cosmological constant. In this approach, the probability to create observers is assumed to be proportional to the entropy production $\Delta S$ in a maximal causally connected region—the causal diamond. We improve on the original treatment by better quantifying the entropy production due to stars, using an analytic model for the star formation history which accurately accounts for changes in cosmological parameters. We calculate the dependence of $\Delta S$ on the density contrast $Q=\delta \rho /\rho$, and find that our universe is much closer to the most probable value of $Q$ than in the usual anthropic approach and that probabilities are relatively weakly dependent on this amplitude. In addition, we make first estimates of the dependence of $\Delta S$ on the baryon fraction and overall matter abundance. Finally, we also explore the possibility that decays of dark matter, suggested by various observed gamma ray excesses, might produce a comparable amount of entropy to stars.

Cosmological phase transitions are predicted by particle physics models, and have a variety of important cosmological consequences, which depend strongly on the dynamics of the transition. In this work we investigate in detail the general features of the development of a first-order phase transition. We find thermodynamical constraints on some quantities that determine the dynamics, namely, the latent heat, the radiation energy density, and the false-vacuum energy density. Using a simple model with a Higgs field, we study numerically the amount and duration of supercooling and the subsequent reheating and phase coexistence. We analyze the dependence of the dynamics on the different parameters of the model, namely, the energy scale, the number of degrees of freedom, and the couplings of the scalar field with bosons and fermions. We also inspect the implications for the cosmological outcomes of the phase transition.

We formulate a field theory for resonantly interacting anyons, that enables us to perform a perturbative calculation near the fermionic limit. We derive renormalization group equations for three-body and four-body couplings at one-loop order. In addition to two fixed points, we find a limit cycle behavior in the four-body coupling, which implies an infinite set of bound states in the four-anyon system.

We present a new truncation scheme for the Schwinger-Dyson equations of QCD that respects gauge invariance at any level of the dressed loop expansion. When applied to the gluon self-energy, it allows for its nonperturbative treatment without compromising the transversality of the solution, even when entire sets of diagrams (most notably the ghost loops) are omitted or treated perturbatively.

We complete and improve the fits to experimental $\pi \pi$ scattering amplitudes, both at low and high energies, that we performed in the previous papers of this series. We then verify that the corresponding amplitudes satisfy analyticity requirements, in the form of partial wave analyticity at low energies, forward dispersion relations (FDR) at all energies, and Roy equations below$\overline{K}K$ threshold; the first by construction, the last two, inside experimental errors. Then we repeat the fits including as constraints FDR and Roy equations. The ensuing central values of the various scattering amplitudes verify very accurately FDR and, especially, Roy equations, and change very little from what we found by just fitting data, with the exception of the D2 wave phase shift, for which one parameter moves by $1.5\sigma$. These improved parametrizations therefore provide a reliable representation of pion-pion amplitudes with which one can test various physical relations. We also present a list of low energy parameters and other observables. In particular, we find $a_0^{(0)}=0.223\pm 0.009M_{\pi }^{-1}$, $a_0^{(2)}=-0.0444\pm 0.0045M_{\pi }^{-1}$, and ${\delta }_0^{(0)}(m_K^2)-{\delta }_0^{(2)}(m_K^2)=50.9\pm {1.2}^{\mathrm{o}}$.

We present a new phenomenological model of the dipole scattering amplitude to demonstrate that the RHIC data for hadron production in $d$-$Au$ collisions for all available rapidities are compatible with geometric scaling, just like the small-$x$ inclusive deep inelastic scattering data. A detailed comparison with earlier geometric scaling violating models of the dipole scattering amplitude in terms of an anomalous dimension $\gamma$ is made. In order to establish whether the geometric scaling violations expected from small-$x$ evolution equations are present in the data a much larger range in transverse momentum and rapidity must be probed. Predictions for hadron production in $p$-$Pb$ and $p$-$p$ collisions at LHC are given. We point out that the falloff of the transverse momentum distribution at LHC is a sensitive probe of the variation of $\gamma$ in a region where $x$ is much smaller than at RHIC. In this way, the expectation for the rise of $\gamma$ from small-$x$ evolution can be tested.

The observed value of the cosmological constant can be naturally related to the scale of breaking down the supersymmetry in consistency with the schemes of gauge and gravity mediation in particle physics, as we argue in the framework of the static description of the phenomenological scalar field with assumed properties of its potential producing the barrier separating the flat vacuum from the anti-de Sitter state, which leads to tuned domain wall fluctuations.

The searches of impulsive gravitational waves (GW) in the data of the ground-based interferometers focus essentially on two types of waveforms: short unmodeled bursts from supernova core collapses and frequency modulated signals (or chirps) from inspiralling compact binaries. There is room for other types of searches based on different models. Our objective is to fill this gap. More specifically, we are interested in GW chirps “in general,” i.e., with an arbitrary phase/frequency vs time evolution. These unmodeled GW chirps may be considered as the generic signature of orbiting or spinning sources. We expect the quasiperiodic nature of the waveform to be preserved independently of the physics which governs the source motion. Several methods have been introduced to address the detection of unmodeled chirps using the data of a single detector. Those include the best chirplet chain (BCC) algorithm introduced by the authors. In the next years, several detectors will be in operation. Improvements can be expected from the joint observation of a GW by multiple detectors and the coherent analysis of their data, namely, a larger sight horizon and the more accurate estimation of the source location and the wave polarization angles. Here, we present an extension of the BCC search to the multiple detector case. This work is based on the coherent analysis scheme proposed in the detection of inspiralling binary chirps. We revisit the derivation of the optimal statistic with a new formalism which allows the adaptation to the detection of unmodeled chirps. The method amounts to searching for salient paths in the combined time-frequency representation of two synthetic streams. The latter are time series which combine the data from each detector linearly in such a way that all the GW signatures received are added constructively. We give a proof of principle for the full-sky blind search in a simplified situation which shows that the joint estimation of the source sky location and chirp frequency is possible.

We investigate the phenomenology of new Abelian gauge bosons, which we denote as $X$ bosons, that suffer a mixed anomaly with the standard model, but are made self-consistent by the Green-Schwarz mechanism. A distinguishing aspect of the resulting effective theory is the decay of $X$ bosons into standard model gauge bosons, $X\to ZZ$, $WW$, $\gamma Z$. We compute the production cross section of the $X$ boson from vector boson fusion at the Large Hadron Collider. We study the $pp\to X\to ZZ\to 4l$ signal, and analyze the prospects of discovery. We argue that such a discovery could indirectly probe high energies, even up to the string scale.

We clarify some properties of projective superspace by using a manifestly superconformal notation. In particular, we analyze the $N=2$ scalar multiplet in detail, including its action, and the propagator and its super-Schwinger parameters. The internal symmetry is taken to be noncompact (after Wick rotation), allowing boundary conditions that preserve it off shell. Generalization to $N=4$ suggests the coset superspace $\mathrm{PSU}(2,2|4)/\mathrm{OSp}(4|4)$ for the AdS/CFT superstring.