We study the resummation of large logarithmic perturbative corrections to the partonic cross sections relevant for dihadron production in hadronic collisions, $H_1{H}_2\to h_1{h}_{2}X$, at high invariant mass of the produced hadron pair. These corrections arise near the threshold for the partonic reaction and are associated with soft-gluon emission. We perform the resummation to next-to-leading logarithmic accuracy, and show how to incorporate consistently cuts in rapidity and transverse momentum of the observed particles. We present numerical results for fixed-target and ISR regimes and find enhancements over the next-to-leading order cross section, which significantly improve the agreement between theoretical predictions and data.

Recently dispersion relations have been applied to hard exclusive processes such as deeply virtual Compton scattering, and a holographic principle was proposed that maps out the generalized parton distributions entering the soft matrix elements for the processes from their values on a given kinematical ridge. We examine possible pitfalls associated with the implicit, direct identification in this approach of the physical hadronic states with colored partons, and suggest an improved treatment of this assumption.

We combine measurements of the top quark pair production cross section in $p\overline{p}$ collisions in the $\ell +\mathrm{\text{jets}}$, $\ell \ell$, and $\tau \ell$ final states (where $\ell$ is an electron or muon) at a center of mass energy of $\sqrt{s}=1.96\mathrm{TeV}$ in $1{\mathrm{fb}}^{-1}$ of data collected with the D0 detector. For a top quark mass of $170\mathrm{GeV}/c^2$, we obtain ${\sigma }_{t\overline{t}}={8.18}_{-0.87}^{+0.98}\mathrm{pb}$ in agreement with the theoretical prediction. Based on predictions from higher order quantum chromodynamics, we extract a mass for the top quark from the combined $t\overline{t}$ cross section, consistent with the world average of the top quark mass. In addition, the ratios of $t\overline{t}$ cross sections in different final states are used to set upper limits on the branching fractions $B(t\to H^{+}b\to {\tau }^{+}\nu b)$ and $B(t\to H^{+}b\to c\overline{s}b)$ as a function of the charged Higgs boson mass.

Motivated by the study of big crunch singularities in asymptotically ${\mathrm{AdS}}_4$ space-times, we consider a marginal triple trace deformation of Aharony-Bergman-Jafferis-Maldacena (ABJM) theory. The deformation corresponds to adding a potential which is unbounded below. In a ’t Hooft large $N$ limit, the beta function for the triple trace deformation vanishes, which is consistent with the near-boundary behavior of the bulk fields. At the next order in the $1/N$ expansion, the triple trace couplings exhibit nontrivial running, which we analyze explicitly in the limit of zero ’t Hooft coupling, in which the model reduces to an $O(N)\times O(N)$ vector model with large $N$. In this limit, we establish the existence of a perturbative UV fixed point, and we comment on possible nonperturbative effects. We also show that the bulk analysis leading to big crunch singularities extends to the ${\mathbb{Z}}_k$ orbifold models dual to ABJM theory.

We show how to represent a class of expressions involving discrete sums over partitions as matrix models. We apply this technique to the partition functions of $2^{*}$ theories, i.e. Seiberg-Witten theories with the massive hypermultiplet in the adjoint representation. We consider theories in four, five, and six dimensions, and obtain new matrix models, respectively, of rational, trigonometric, and elliptic type. The matrix models for five- and six-dimensional $U(1)$ theories are derived from the topological vertex construction related to curves of genus one and two.

Dark energy perturbations are normally either neglected or else included in a purely numerical way, obscuring their dependence on underlying parameters like the equation of state or the sound speed. However, while many different explanations for the dark energy can have the same equation of state, they usually differ in their perturbations so that these provide a fingerprint for distinguishing between different models with the same equation of state. In this paper we derive simple yet accurate approximations that are able to characterize a specific class of models (encompassing most scalar-field models) which is often generically called “dark energy.” We then use the approximate solutions to look at the impact of the dark energy perturbations on the dark matter power spectrum and on the integrated Sachs-Wolfe effect in the cosmic microwave background radiation.

We derive expressions for pion electroproduction amplitudes in the $1/N_c$ expansion of QCD, and obtain from them linear relations between the electromagnetic multipole amplitudes that hold at all energies. The leading-order relations in $1/N_c$ compare favorably with available data (especially away from resonances), but the next-to-leading-order relations tend to provide only small or no improvement.

We show that, if a fourth generation is discovered at the Tevatron or LHC, one could study $CP$ violation (CPV) in $b^{\prime }\to s$ decays. Asymmetries could reach 30% for $b^{\prime }\to sZ$ for $m_{b^{\prime }}\lesssim 350\mathrm{GeV}$, while it could be greater than 50% for $b^{\prime }\to s\gamma$ and extend to higher $m_{b^{\prime }}$. Branching ratios are ${10}^{-3}–{10}^{-5}$, and CPV measurement requires tagging. Once measured, however, the CPV phase can be extracted with little theoretical uncertainty.

We study lepton flavor-violating (LFV) processes within a supersymmetric type-I seesaw framework with flavor-blind universal boundary conditions, properly accounting for the effect of the neutrino sector on the dark matter relic abundance. We consider several possibilities for the neutrino Yukawa coupling matrix and show that in regions of SUSY parameter space that yield the correct neutralino relic density, LFV rates can differ from naive estimates by up to 2 orders of magnitude. Contrary to common belief, we find that current LFV limits do not exclude neutrino Yukawa couplings larger than top Yukawa couplings. We introduce the ISAJET-M program that was used for the computations.

The rates at which the mass and angular momentum of a small black hole change as a result of a tidal interaction with a much larger black hole are calculated to leading order in the small mass ratio. The small black hole is either rotating or nonrotating, and it moves on a circular orbit in the equatorial plane of the large Kerr black hole. The orbits are fully relativistic, and the rates are computed to all orders in the orbital velocity $V\le V_{\mathrm{isco}}$, which is limited only by the size of the innermost stable circular orbit. We show that as $V\to V_{\mathrm{isco}}$, the rates take on a limiting value that depends only on $V_{\mathrm{isco}}$ and not on the spin parameter of the large black hole.

Generic model predictions for the early neutrino signal of a core-collapse supernova (SN) imply that IceCube can reconstruct the bounce to within about $\pm 3.5\mathrm{ms}$ at 95% C.L. (assumed SN distance 10 kpc), relevant for coincidence with gravitational-wave detectors. The timing uncertainty scales approximately with the distance squared. The offset between true and reconstructed bounce time of up to several ms depends on the neutrino flavor oscillation scenario. Our work extends the recent study of Pagliaroli et al. [Phys. Rev. Lett. 103, 031102 (2009)] and demonstrates IceCube’s superb timing capabilities for neutrinos from the next nearby SN.

We discuss the conditions under which classically conformally invariant models in four dimensions can arise out of nonconformal (Einstein) gravity. As an “existence proof” that this is indeed possible we show how to derive $N=4$ super Yang-Mills theory with any compact gauge group $G$ from nonconformal gauged $N=4$ supergravity as a special flat space limit. We stress the role that the anticipated UV finiteness of the (so far unknown) underlying theory of quantum gravity would have to play in such a scheme, as well as the fact that the masses of elementary particles would have to arise via quantum gravitational effects which mimic the conformal anomalies of standard (flat space) UV divergent quantum field theory.

We argue that the existence of dark matter (DM) is a possible consequence of grand unification (GUT) symmetry breaking. In GUTs like $SO(10)$, discrete $Z_2$ matter parity $(-1{)}^{3(B-L)}$ survives despite broken $B-L$, and group theory uniquely determines that the only possible $Z_2$-odd matter multiplets belong to representation $\mathbf{16}$. We construct the minimal nonsupersymmetric $SO(10)$ model containing one scalar $\mathbf{16}$ for DM and study its predictions below $M_G$. We find that electroweak symmetry breaking occurs radiatively due to DM couplings to the standard model Higgs boson. For thermal relic DM the mass range $M_{\mathrm{DM}}\sim \mathcal{O}(0.1–1)\mathrm{TeV}$ is predicted by model perturbativity up to $M_G$. For $M_{\mathrm{DM}}\sim \mathcal{O}(1)\mathrm{TeV}$ to explain the observed cosmic ray anomalies with DM decays, there exists a lower bound on the spin-independent direct detection cross section within the reach of planned experiments.

We study the dynamical breaking of chiral and color symmetries of dense quark matter in the ultrastatic hyperbolic spacetime $R\otimes H^3$ in the framework of an extended Nambu–Jona-Lasinio model. On the basis of analytical expressions for chiral and color condensates as functions of curvature and temperature, the phenomenon of dimensional reduction and gravitational catalysis of symmetry breaking in strong gravitational field is demonstrated in the regime of weak coupling constants. In the case of strong couplings it is shown that curvature leads to small corrections to the flat-space values of condensate and thus enhances the symmetry breaking effects. Finally, using numerical calculations phase transitions under the influence of chemical potential and negative curvature are considered and the phase portrait of the system is constructed.

We study the nonperturbative behavior of two versions of the QCD effective charge, one obtained from the pinch technique gluon self-energy, and one from the ghost-gluon vertex. Despite their distinct theoretical origin, due to a fundamental identity relating various ingredients appearing in their respective definitions, the two effective charges are almost identical in the entire range of physical momenta, and coincide exactly in the deep infrared, where they freeze at a common finite value. Specifically, the dressing function of the ghost propagator is related to the two form factors in the Lorentz decomposition of a certain Green’s function, appearing in a variety of field-theoretic contexts. The central identity, which is valid only in the Landau gauge, is derived from the Schwinger-Dyson equations governing the dynamics of the aforementioned quantities. The renormalization procedure that preserves the validity of the identity is carried out, and various relevant kinematic limits and physically motivated approximations are studied in detail. A crucial ingredient in this analysis is the infrared finiteness of the gluon propagator, which is inextricably connected with the aforementioned freezing of the effective charges. Some important issues related to the consistent definition of the effective charge in the presence of such a gluon propagator are resolved. We finally present a detailed numerical study of a special set of Schwinger-Dyson equations, whose solutions determine the nonperturbative dynamics of the quantities composing the two effective charges.

A new class of models of dynamical supersymmetry breaking is proposed. The models are based on $SU(N_C)$ gauge theories with $N_F(<N_C)$ flavors of quarks and singlets. Dynamically generated superpotential exhibits runaway behavior. By embedding the models into conformal field theories at high energies, the runaway potential is stabilized by strong quantum corrections to the Kähler potential. The quantum corrections are large but nevertheless can be controlled due to superconformal symmetry of the theories.

We present spherically symmetric boson stars as black hole mimickers based on the power spectrum of a simple accretion disk model. The free parameters of the boson star are the mass of the boson and the fourth-order self-interaction coefficient in the scalar field potential. We show that even if the mass of the boson is the only free parameter, it is possible to find a configuration that mimics the power spectrum of the disk due to a black hole of the same mass. We also show that for each value of the self-interaction a single boson star configuration can mimic a black hole at very different astrophysical scales in terms of the mass of the object and the accretion rate. In order to show that it is possible to distinguish one of our mimickers from a black hole, we also study the deflection of light.

We study the impact of a running index ${\alpha }_t$ on the spectrum of relic gravitational waves (RGWs) over the whole range of frequency $({10}^{-18}\sim {10}^{10})\mathrm{Hz}$ and reveal its implications in RGWs detections and in cosmology. Analytical calculations show that, although the spectrum of RGWs on low frequencies is less affected by ${\alpha }_t\ne 0$, on high frequencies, the spectrum is modified substantially. Investigations are made toward potential detections of the ${\alpha }_t$-modified RGWs for several kinds of current and planned detectors. The Advanced LIGO will likely be able to detect RGWs with ${\alpha }_t\ge 0$ for inflationary models with the inflation index $\beta =-1.956$ and the tensor-scalar ratio $r=0.55$. The future LISA can detect RGWs for a much broader range of $({\alpha }_t,\beta ,r)$, and will have a better chance to break a degeneracy between them. Constraints on ${\alpha }_t$ are estimated from several detections and cosmological observations. Among them, the most stringent one is from the bound of the big bang nucleosynthesis, and requires ${\alpha }_t<0.008$ rather conservatively for any reasonable $(\beta ,r)$, preferring a nearly power-law spectrum of RGWs. In light of this result, one would expect the scalar running index ${\alpha }_s$ to be of the same magnitude as ${\alpha }_t$, if both RGWs and scalar perturbations are generated by the same scalar inflation.

Prescriptions for numerical self-force calculations have traditionally been designed for frequency-domain or ($1+1$) time-domain codes which employ a mode decomposition to facilitate in carrying out a delicate regularization scheme. This has prevented self-force analyses from benefiting from the powerful suite of tools developed and used by numerical relativists for simulations of the evolution of comparable-mass black hole binaries. In this work, we revisit a previously-introduced ($3+1$) method for self-force calculations and demonstrate its viability by applying it to the test case of a scalar charge moving in a circular orbit around a Schwarzschild black hole. Two ($3+1$) codes originally developed for numerical relativity applications were independently employed, and in each we were able to compute the two independent components of the self-force and the energy flux correctly to within $<1\%$. We also demonstrate consistency between the $t$ component of the self-force and the scalar energy flux. Our results constitute the first successful calculation of a self-force in a ($3+1$) framework, and thus open opportunities for the numerical relativity community in self-force analyses and the perturbative modeling of extreme-mass-ratio inspirals.

We numerically study the scalar perturbation of a rotating black hole in anti–de Sitter spacetime (Kerr-AdS black hole). It is found that small Kerr-AdS black holes characterized by $r_{+}\lesssim 0.16\ell$ are unstable against scalar perturbations via the superradiant amplification mechanism for some rotation rates, where $r_{+}$ and $\ell$ stand, respectively, for the radial coordinate value of the black hole event horizon in the Boyer-Lindquist coordinates and the cosmological length-scale, defined by $\ell =(-3/\Lambda {)}^{1/2}$. Here $\Lambda$ is the (negative) cosmological constant.