We estimate the contributions by double-parton interactions to the cross sections for $pp\to {\pi }^0{\pi }^{0}X$ and $dA\to {\pi }^0{\pi }^{0}X$ at the Relativistic Heavy Ion Collider (RHIC). We find that such contributions become important at large forward rapidities of the produced pions. This is, in particular, the case for $dA$ scattering, where they strongly enhance the azimuthal-angular independent pedestal component of the cross section, providing a natural explanation of this feature of the RHIC $dA$ data. We argue that the discussed processes open a window to studies of double quark distributions in nucleons. We also briefly address the roles of shadowing and energy loss in $dA$ scattering, which we show to affect the double-inclusive pion cross section much more strongly than the single-inclusive one. We discuss the implications of our results for the interpretation of pion azimuthal correlations.

The double parton distribution functions are investigated in the region of small longitudinal momentum fractions in the leading logarithm approximation of perturbative QCD. It is shown that these functions have the factorization property in the case of one slow and one fast parton.

A next-generation liquid-scintillator detector will be able to perform high-statistics measurements of the solar neutrino flux. In LENA, solar ${}^7\mathrm{Be}$ neutrinos are expected to cause $1.7\times {10}^4$ electron recoil events per day in a fiducial volume of 35 kilotons. Based on this signal, a search for periodic modulations on a subpercent level can be conducted, surpassing the sensitivity of current detectors by at least a factor of 20. The range of accessible periods reaches from several minutes, corresponding to modulations induced by helioseismic g-modes, to tens of years, allowing to study long-term changes in solar fusion rates.

The $p$-wave and $p+ip$-wave holographic superconductors with fixed DC supercurrent are studied by introducing a nonvanishing vector potential. We find that close to the critical temperature $T_c$ of zero current, the numerical results of both the $p$-wave model and the $p+ip$ model are the same as those of Ginzburg-Landau (GL) theory; for example, the critical current is $j_c\sim (T_c-T{)}^{3/2}$ and the phase transition in the presence of a DC current is a first-order transition. Beside the similar results between both models, the $p+ip$ superconductor shows isotropic behavior for the supercurrent, while the $p$-wave superconductor shows anisotropic behavior for the supercurrent.

We show how expansions in powers of Planck’s constant $\hslash =h/2\pi$ can give new insights into perturbative and nonperturbative properties of quantum field theories. Since $\hslash$ is a fundamental parameter, exact Lorentz invariance and gauge invariance are maintained at each order of the expansion. The physics of the $\hslash$ expansion depends on the scheme; i.e., different expansions are obtained depending on which quantities (momenta, couplings, and masses) are assumed to be independent of $\hslash$. We show that if the coupling and mass parameters appearing in the Lagrangian density are taken to be independent of $\hslash$, then each loop in perturbation theory brings a factor of $\hslash$. In the case of quantum electrodynamics, this scheme implies that the classical charge $e$, as well as the fine structure constant are linear in $\hslash$. The connection between the number of loops and factors of $\hslash$ is more subtle for bound states since the binding energies and bound-state momenta themselves scale with $\hslash$. The $\hslash$ expansion allows one to identify equal-time relativistic bound states in QED and QCD which are of lowest order in $\hslash$ and transform dynamically under Lorentz boosts. The possibility to use retarded propagators at the Born level gives valencelike wave functions which implicitly describe the sea constituents of the bound states normally present in its Fock state representation.

In this paper, we derive a critical condition for matter equilibration in heavy ion collisions using a holographic approach. Gravitational shock waves with infinite transverse extension are used to model an infinite nucleus. We construct the trapped surface in the collision of two asymmetric planar shock waves with sources at different depth in the bulk AdS and formulate a critical condition for matter equilibration in the collision of “nuclei” in the dual gauge theory. We find the critical condition is insensitive to the depth of the source closer to the AdS boundary. To understand the origin of the critical condition, we compute the Next-to-Leading Order stress tensor in the boundary field theory due to the interaction of the nuclei and find that the critical condition corresponds to the breaking down of the perturbative expansion. We expect nonperturbative effects are needed to describe black hole formation.

We show, by using an extensive sample of viable supersymmetric models as templates, that indirect detection of dark matter through gamma rays may have a large potential for identifying the nature of dark matter. This is, in particular, true also for models that give too weak dark matter-nucleon scattering cross sections to be probed by present and planned direct detection experiments. Also models with a mass scale too high to be accessible at CERN’s LHC accelerator may show up in next-generation imaging Cherenkov telescope arrays. Based on our findings, we therefore suggest to view indirect searches as genuine particle physics experiments, complementing other strategies to probe so far unknown regions in the parameter space of e.g. supersymmetric models, and propose a new approach that would make use of telescopes dedicated for dark matter searches. As a concrete example for the potential of such an approach, we consider an array of imaging air Cherenkov telescopes, the Dark Matter Array (DMA), and show that such an experiment could extend present-day limits by several orders of magnitude, reaching a large class of models that would remain undetected in both direct detection experiments and searches at the LHC. In addition, in a sizable part of the parameter space, signals from more than one type of dark matter detection experiment would be possible, something that may eventually be necessary in order to identify the dark matter candidate.

We analyze quantization of noncommutative chiral electrodynamics in the enveloping algebra formalism in linear order in noncommutativity parameter $\theta$. Calculations show that divergences exist and cannot be removed by ordinary renormalization; however, they can be removed by the Seiberg-Witten redefinition of fields. Performing redefinitions explicitly, we obtain renormalizable Lagrangian and discuss the influence of noncommutativity on field propagation. Noncommutativity affects the propagation of chiral fermions only: half of the fermionic modes become massive and birefringent.

The Wilson coefficients for all 4-parton operators which arise in matching QCD to soft-collinear effective theory (SCET) are computed at 1-loop. Any dijet observable calculated in SCET beyond leading order will require these results. The Wilson coefficients are separated by spin and color, although most applications will involve only the spin-averaged hard functions. The anomalous dimensions for the Wilson coefficients are given to 2-loop order, and the renormalization group equations are solved explicitly. This will allow for analytical resummation of dijet observables to next-to-next-to-leading logarithmic accuracy. For each channel, there is a natural basis in which the evolution is diagonal in color space. The same basis also diagonalizes the color evolution for the soft function. Even though soft functions required for SCET calculations are observable dependent, it is shown that their renormalization group evolution is almost completely determined by a universal structure. With these results, it will be possible to calculate hadronic event shapes or other dijet observables to next-to-leading order with next-to-next-to-leading log resummation.

We propose a stochastic method for solving Schwinger-Dyson equations in large-$N$ quantum field theories. Expectation values of single-trace operators are sampled by stationary probability distributions of the so-called nonlinear random processes. The set of all the histories of such processes corresponds to the set of all planar diagrams in the perturbative expansions of the expectation values of singlet operators. We illustrate the method on examples of the matrix-valued scalar field theory and the Weingarten model of random planar surfaces on the lattice. For theories with compact field variables, such as sigma models or non-Abelian lattice gauge theories, the method does not converge in the physically most interesting weak-coupling limit. In this case one can absorb the divergences into a self-consistent redefinition of expansion parameters. A stochastic solution of the self-consistency conditions can be implemented as a “memory” of the random process, so that some parameters of the process are estimated from its previous history. We illustrate this idea on the two-dimensional $O(N)$ sigma model. The extension to non-Abelian lattice gauge theories is discussed.

We present results from a new code for binary black hole evolutions using the moving-puncture approach, implementing finite differences in generalized coordinates, and allowing the spacetime to be covered with multiple communicating nonsingular coordinate patches. Here we consider a regular Cartesian near-zone, with adapted spherical grids covering the wave zone. The efficiencies resulting from the use of adapted coordinates allow us to maintain sufficient grid resolution to an artificial outer boundary location which is causally disconnected from the measurement. For the well-studied test case of the inspiral of an equal-mass nonspinning binary (evolved for more than 8 orbits before merger), we determine the phase and amplitude to numerical accuracies better than 0.010% and 0.090% during inspiral, respectively, and 0.003% and 0.153% during merger. The waveforms, including the resolved higher harmonics, are convergent and can be consistently extrapolated to $r\to \infty$ throughout the simulation, including the merger and ringdown. Ringdown frequencies for these modes (to $(\ell ,m)=(6,6)$) match perturbative calculations to within 0.01%, providing a strong confirmation that the remnant settles to a Kerr black hole with irreducible mass $M_{\mathrm{irr}}=0.884355\pm 20\times {10}^{-6}$ and spin $S_f/M_f^2=0.686923\pm 10\times {10}^{-6}$.

We show that the inclusion of an axionlike effective potential in the construction of a self-gravitating system of scalar fields decreases its compactness when the value of the self-interaction coupling constant is increased. By including the current values for the axion mass $m$ and decay constant $f_a$, we have computed the mass and the radius for self-gravitating systems made of axion particles. It is found that such objects will have asteroid size masses and radii of a few meters, thus a self-gravitating system made of axions could play the role of scalar mini-MACHOs and mimic a cold dark matter model for the galactic halo.

In this short note we translate the best available observational bounds on the CMB bispectrum amplitudes into constraints on a specific scale-invariant new physics hypersurface model of vacuum state modifications, as first proposed by Danielsson, in general models of single-field inflation. As compared to the power spectrum the bispectrum constraints are less ambiguous and provide an interesting upper bound on the cutoff scale in general models of single-field inflation with a small speed of sound. This upper bound is incompatible with the power spectrum constraint for most of the parameter domain, leaving very little room for minimal cutoff vacuum state modifications in general single-field models with a small speed of sound.

We report on a study of exclusive radiative decays of the ${\rm Y}(1\mathrm{S})$ resonance into a final state consisting of a photon and two $K_{\mathrm{S}}^0$ candidates. We find evidence for a signal for ${\rm Y}(1\mathrm{S})\to \gamma f_2^{\prime }(1525)$; $f_2^{\prime }(1525)\to \gamma K_{\mathrm{S}}^0{K}_{\mathrm{S}}^0$, at a rate $\mathcal{B}({\rm Y}(1\mathrm{S})\to \gamma f_2^{\prime }(1525))=(4.0\pm 1.3\pm 0.6)\times {10}^{-5}$, consistent with previous observations of ${\rm Y}(1\mathrm{S})\to \gamma f_2^{\prime }(1525)$; $f_2^{\prime }(1525)\to K^{+}{K}^{-}$, and isospin. Combining this branching fraction with existing branching fraction measurements of ${\rm Y}(1\mathrm{S})\to \gamma f_2^{\prime }(1525)$ and $J/\psi \to \gamma f_2^{\prime }(1525)$, we obtain the ratio of branching fractions: $\mathcal{B}({\rm Y}(1\mathrm{S})\to \gamma f_2^{\prime }(1525))/\mathcal{B}(J/\psi \to \gamma f_2^{\prime }(1525))=0.09\pm 0.02$, approximately consistent with expectations based on soft-collinear effective theory.

In theories with universal extra dimensions (UED), the ${\gamma }_1$ particle, first excited state of the hypercharge gauge boson, provides an excellent dark matter (DM) candidate. Here, we use a modified version of the SuperBayeS code to perform a Bayesian analysis of the minimal UED scenario, in order to assess its detectability at accelerators and with DM experiments. We derive, in particular, the most probable range of mass and scattering cross sections off nucleons, keeping into account cosmological and electroweak precision constraints. The consequences for the detectability of the ${\gamma }_1$ with direct and indirect experiments are dramatic. The spin-independent cross section probability distribution peaks at $\sim {10}^{-11}\mathrm{pb}$, i.e. below the sensitivity of ton-scale experiments. The spin-dependent cross section drives the predicted neutrino flux from the center of the Sun below the reach of present and upcoming experiments. The only strategy that remains open appears to be direct detection with ton-scale experiments sensitive to spin-dependent cross sections. On the other hand, the LHC with $1{\mathrm{fb}}^{-1}$ of data should be able to probe the current best-fit UED parameters.

We evaluate the radion and Higgs masses in the gauge-Higgs unification models on the warped geometry, in which the modulus is stabilized by the Casimir energy. We analyze the one-loop effective potential and clarify the dependences of those masses on the Wilson line phase ${\theta }_{\mathrm{H}}$. The radion mass varies 1–30 GeV for $0.06\le \sin {\theta }_{\mathrm{H}}\le 0.3$, while the Higgs mass is 150–200 GeV and depends on ${\theta }_{\mathrm{H}}$ only logarithmically. The radion couplings to the standard model particles are sensitive to the warp factor, and are too small to detect at colliders in the region where the five-dimensional description is valid.

We discuss in detail the flavor structure of the supersymmetric $SO(10)$ grand unified models with the three traditional 16-dimensional matter spinors mixed with a set of extra ten-dimensional vector multiplets which can provide the desired sensitivity of the standard model matter spectrum to the grand unified theory symmetry breakdown at the renormalizable level. We put the qualitative argument that a successful fit of the quark and lepton data requires an active participation of more than a single vector matter multiplet on a firm, quantitative ground. We find that the strict no-go obtained for the fits of the charged-sector observables in case of a single active matter 10 is relaxed if a second vector multiplet is added to the matter sector and excellent, though nontrivial, fits can be devised. Exploiting the unique calculable part of the neutrino mass matrix governed by the $SU(2{)}_L$ triplet in the 54-dimensional Higgs multiplet, a pair of genuine predictions of the current setting is identified: a nonzero value of the leptonic 1–3 mixing close to the current 90% C.L. limit and a small leptonic Dirac $CP$ phase are strongly preferred by all solutions with the global-fit ${\chi }^2$ values below 50.

We study the effects of the fourth generation of quarks on the total branching ratio and the lepton polarizations in ${\overline{B}}_0\to K_0^{*}(1430)l^{+}{l}^{-}$ ($l=\mu$, $\tau$) decay. Taking the fourth generation quark mass $m_{t\prime }$ of about 400 to 600 GeV with the mixing angle $|V_{t^{\prime }b}^{*}{V}_{t^{\prime }s}|$ in the range $(0.05–1.4)\times {10}^{-2}$ and using the phase to be 80°, it is found that the branching ratio and lepton polarizations are quite sensitive to these fourth generation parameters. In the future, the experimental study of this decay will give us an opportunity to study new physics effects, precisely, to search for the fourth generation of quarks $(t^{\prime },b^{\prime })$ in an indirect way.

We calculate the vector current correlation function for light valence quarks in the deconfined phase of QCD. The calculations have been performed in quenched lattice QCD at $T\simeq 1.45T_c$ for four values of the lattice cutoff on lattices up to size ${128}^3\times 48$. This allows us to perform a continuum extrapolation of the correlation function in the Euclidean time interval $0.2\le \tau T\le 0.5$, which extends to the largest temporal separations possible at finite temperature, to better than 1% accuracy. In this interval, at the value of the temperature investigated, we find that the vector correlation function never deviates from the free correlator for massless quarks by more than 9%. We also determine the first two nonvanishing thermal moments of the vector meson spectral function. The second thermal moment deviates by less than 7% from the free value. With these constraints, we then proceed to extract information on the spectral representation of the vector correlator and discuss resulting consequences for the electrical conductivity and the thermal dilepton rate in the plasma phase.