In this paper we study photon production in single and double diffractive processes considering the resolved pomeron model. We estimate the rapidity and transverse momentum dependence of the cross section for the diffractive double photon and $\mathrm{\text{photon}}+\mathrm{\text{jet}}$ production. A comparison with the inclusive production is presented. We predict large values for the total cross sections, which make the experimental analysis of these observables feasible at LHC energies.

We present a study of proton generalized parton distributions (GPDs) in both momentum and position spaces using the proton wave function obtained from AdS/QCD. Here we consider the soft wall model. The results are compared with a phenomenological model of proton GPDs.

Recent work in the literature has argued that the joint effect of spacetime curvature and the Gribov ambiguity may introduce further modifications to the Green functions in the infrared. This paper focuses on a simple criterion for studying the effect of spacetime curvature on the size of the Gribov region, improving the accuracy of the previous analysis. It is shown that, depending on the sign of the scalar and Riemann curvature, the Gribov horizon moves inward or, instead, outward with respect to the case of flat spacetime. This is made clear by two novel inequalities, derived here for the first time.

We present new constraints on possible features in the primordial inflationary density perturbation power spectrum in light of the recent cosmic microwave background anisotropy measurements from the Planck satellite. We found that the Planck data hints for the presence of features in two different ranges of angular scales, corresponding to multipoles $10<\ell <60$ and $150<\ell <300$, with a decrease in the best-fit ${\chi }^2$ value with respect to the featureless “vanilla” $\Lambda \mathrm{CDM}$ model of $\Delta {\chi }^2\simeq 9$ in both cases.

We point that any theoretically found value for an electromagnetic multipole of a baryon or a meson should be subjected to “renormalization” due to nonlinearity of QED. We find third-power nonlinear corrections to the Coulomb and other static electric fields, as well as to the electric and magnetic dipole fields, as we work within QED with no background field. The nonlinear response function on which we base our consideration is the fourth-rank polarization tensor, calculated within the local (infrared) approximation of the effective action, the results being applicable to weakly varying and not too strong fields. It is established that the nonlinear corrections to magnetic moments of some baryons and mesons, fitting the present approximate scheme, match the existing indeterminacy in their theoretical values.

We consider the challenging problem of obtaining an analytic understanding of realistic astrophysical dynamics in the presence of a Vainshtein screened fifth force arising from infrared modifications of general relativity. In particular, we attempt to solve—within the most general flat spacetime Galileon model—the scalar force law between well separated bodies located well within the Vainshtein radius of the Sun. To this end, we derive the exact static Green’s function of the Galileon wave equation linearized about the background field generated by the Sun, for the minimal cubic and maximally quartic Galileon theories, and then introduce a method to compute the general leading order force law perturbatively away from these limits. We also show that the same nonlinearities which produce the Vainshtein screening effect present obstacles to an analytic calculation of the Galileon forces between closely bound systems within the Solar System, such as that of the Earth and Moon. Within the test mass approximation, we deduce that a large enough quartic Galileon interaction would suppress the effect on planetary perihelion precession below the level detectable by even the next-generation experiments.

Employing Fermi-LAT gamma-ray observations, several independent groups have found excess extended gamma-ray emission at the Galactic Center (GC). Both annihilating dark matter (DM) or a population of $\sim {10}^3$ unresolved millisecond pulsars (MSPs) are regarded as well-motivated possible explanations. However, there are significant uncertainties in the diffuse galactic background at the GC. We have performed a revaluation of these two models for the extended gamma-ray source at the GC by accounting for the systematic uncertainties of the Galactic diffuse emission model. We also marginalize over point-source and diffuse background parameters in the region of interest. We show that the excess emission is significantly more extended than a point source. We find that the DM (or pulsar-population) signal is larger than the systematic errors and therefore proceed to determine the sectors of parameter space that provide an acceptable fit to the data. We find that a population of 1000–2000 MSPs with parameters consistent with the average spectral shape of Fermi-LAT measured MSPs is able to fit the GC excess emission. For DM, we find that a pure ${\tau }^{+}{\tau }^{-}$ annihilation channel is not a good fit to the data. But a mixture of ${\tau }^{+}{\tau }^{-}$ and $b\overline{b}$ with a $⟨\sigma v⟩$ of order the thermal relic value and a DM mass of around 20 to 60 GeV provides an adequate fit.

A perfect irrotational fluid with the equation of state of dust, irrotational dark matter (IDM), is incapable of virializing and instead forms a cosmoskeleton of filaments with supermassive black holes at the joints. This stark difference from the standard cold dark matter scenario arises because IDM must exhibit potential flow at all times, preventing shell crossing from occurring. This scenario is applicable to general nonoscillating scalar-field theories with a small sound speed. Our model of combined IDM and cold dark matter components thereby provides a solution to the problem of forming the observed billion-solar-mass black holes at redshifts of six and higher. In particular, as a result of the reduced vortical flow, the growth of the black holes is expected to be more rapid at later times as compared to the standard scenario.

We determine the decay constants of the $\pi$ and $K$ mesons on gluon field configurations from the MILC Collaboration including $u$, $d$, $s$, and $c$ quarks. We use three values of the lattice spacing and $u/d$ quark masses going down to the physical value. We use the $w_0$ parameter to fix the relative lattice spacing and $f_{\pi }$ to fix the overall scale. This allows us to obtain a value for $f_{K^{+}}/f_{{\pi }^{+}}=1.1916(21)$. Comparing to the ratio of experimental leptonic decay rates gives $|V_{us}|=0.22564(28{)}_{\mathrm{Br}(K^{+})}(20{)}_{\mathrm{EM}}(40{)}_{\mathrm{latt}}(5{)}_{V_{ud}}$ and the test of unitarity of the first row of the Cabibbo-Kobayashi-Maskawa matrix: $|V_{ud}{|}^2+|V_{us}{|}^2+|V_{ub}{|}^2-1=0.00009(51)$.

We study the contribution of the twist-3 fragmentation function to the single-transverse spin asymmetry in semi-inclusive deep inelastic scattering within the framework of the collinear factorization. Making use of the Ward-Takahashi identity in QCD, we establish the formalism in the Feynman gauge to calculate the nonpole contribution of the twist-3 fragmentation function to the asymmetry and derive the complete cross-section formula in the leading-order QCD perturbation theory. The obtained twist-3 hadronic tensor is shown to satisfy the electromagnetic gauge invariance. The behavior in the small transverse-momentum region for the five structure functions is also given.

We make a comparative and comprehensive study on the charmonium-exclusive productions at the $e^{+}{e}^{-}$ collider with the collision energy either round the $Z^0$-boson mass for a super $Z$ factory or equal to 10.6 GeV for the $B$ factories as Belle and BABAR. We study the total cross sections for the charmonium production via the exclusive processes $e^{+}{e}^{-}\to {\gamma }^{*}/Z^0\to H_1+H_2$ and $e^{+}{e}^{-}\to {\gamma }^{*}/Z^0\to H_1+\gamma$, where $H_1$ and $H_2$ represent the dominant color-singlet $S$-wave and $P$-wave charmonium states, respectively. Total cross sections versus the $e^{+}{e}^{-}$ collision energy $\sqrt{s}$, together with their uncertainties, are presented, which clearly show the relative importance of these channels. At the $B$ factory, the production channels via the virtual ${\gamma }^{*}$ propagator are dominant over the channels via the $Z^0$ propagator by about 4 orders. While at the super $Z$ factory, due to the $Z^0$-boson resonance effect, the $Z^0$ boson channels shall provide sizable or even dominant contributions in comparison to the channels via the ${\gamma }^{*}$ propagator. Sizable exclusive charmonium events can be produced at the super $Z$ factory with high luminosity up to ${10}^{36}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$, especially for the channel of $e^{+}{e}^{-}\to Z^0\to H_1+\gamma$; e.g., by taking $m_c=1.50\pm 0.20\mathrm{GeV}$, we shall have $({5.0}_{-0.6}^{+0.8})\times {10}^4$ $J/\psi$, $({7.5}_{-0.9}^{+1.1})\times {10}^3$ ${\eta }_c$, $({6.2}_{-1.9}^{+3.3})\times {10}^3$ $h_c$, $({3.1}_{-0.9}^{+1.7})\times {10}^2$ ${\chi }_{c0}$, $({2.2}_{-0.4}^{+1.0})\times {10}^3$ ${\chi }_{c1}$, and $({7.7}_{-2.4}^{+4.1})\times {10}^2$ ${\chi }_{c2}$ events in one operation year. Thus, in addition to the $B$ factories as BABAR and Belle, such a super $Z$ factory shall provide another useful platform for studying the heavy quarkonium properties and for testing QCD theories.

We study single jet production in electron-nucleus collisions $e^{-}+N_A\to J+X$, using the 1-jettiness (${\tau }_1$) global event shape. It inclusively quantifies the pattern of radiation in the final state, gives enhanced sensitivity to soft radiation at wide angles from the nuclear beam and final-state jet, and facilitates the resummation of large Sudakov logarithms associated with the veto on additional jets. Through their effect on the observed pattern of radiation, 1-jettiness can be a useful probe of nuclear parton distribution functions and power corrections from dynamical effects in the nuclear medium. This formalism allows for the standard jet shape analysis while simultaneously providing sensitivity to soft radiation at wide angles from the jet. We use a factorization framework for cross-sections differential in ${\tau }_1$ and the transverse momentum ($P_{J_T}$) and rapidity ($y$) of the jet, in the region ${\tau }_1\ll P_{J_T}$. The restriction ${\tau }_1\ll P_{J_T}$ allows only soft radiation between the nuclear beam and jet directions, thereby acting as a veto on additional jets. This region is also insensitive to the details of the jet algorithm, allowing for better theoretical control over resummation, while providing enhanced sensitivity to nuclear medium effects. We give numerical results at leading twist, with resummation at the next-to-next-to-leading logarithmic level of accuracy, for a variety of nuclear targets. Such studies would be ideal for the electron-ion collider and the LHeC proposals for a future electron-ion collider, where a range of nuclear targets are planned.

We study the process of associated photon and jet production, $p\overline{p}\to \gamma +\mathrm{\text{jet}}+X$, using $8.7{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the D0 detector at the Fermilab Tevatron Collider at a center-of-mass energy $\sqrt{s}=1.96\mathrm{TeV}$. Photons are reconstructed with rapidity $|y^{\gamma }|<1.0$ or $1.5<|y^{\gamma }|<2.5$ and transverse momentum $p_T^{\gamma }>20\mathrm{GeV}$. The highest-$p_T$ jet is required to be in one of four rapidity regions up to $|y^{\mathrm{jet}}|\le 3.2$. For each rapidity configuration we measure the differential cross sections in $p_T^{\gamma }$ separately for events with the same sign ($y^{\gamma }{y}^{\mathrm{jet}}>0$) and opposite signs ($y^{\gamma }{y}^{\mathrm{jet}}\le 0$) of photon and jet rapidities. We compare the measured triple-differential cross sections, ${\mathrm{d}}^3\sigma /\mathrm{d}{p}_T^{\gamma }\mathrm{d}{y}^{\gamma }\mathrm{d}{y}^{\mathrm{jet}}$, to next-to-leading order (NLO) perturbative QCD calculations using different sets of parton distribution functions, and to predictions from the sherpa and pythia Monte Carlo event generators. The NLO calculations are found to be in general agreement with the data but do not describe all kinematic regions.

We examine a cosmological scenario where dark matter is coupled to a variable vacuum energy while baryons and photons are two decoupled components for a spatially flat Friedmann-Robertson-Walker spacetime. We apply the ${\chi }^2$ method to the updated observational Hubble data for constraining the cosmological parameters and analyze the amount of dark energy in the radiation era. We show that our model fulfills the severe bound of ${\Omega }_x(z\simeq 1100)<0.009$ at the $2\sigma$ level, so it is consistent with the recent analysis that includes cosmic microwave background anisotropy measurements from the Planck survey, the Atacama Cosmology Telescope, and the South Pole Telescope along with the future constraints achievable by the Euclid and CMBPol experiments, and fulfills the stringent bound ${\Omega }_x(z\simeq {10}^{10})<0.04$ at the $2\sigma$ level in the big-bang nucleosynthesis epoch.

We study the low-energy and low-momentum behavior of current correlators in a class of holographic zero-temperature, finite-density critical theories which do not respect the hyperscaling relation. The dual holographic description is assumed to be given by probe D-branes embedded in background geometries characterized by a dynamical critical exponent $z$ and a hyperscaling violation exponent $\theta$. We show that a subset of these theories with $1\le z<2(1-\theta /d)$ exhibit a stable, linearly dispersing mode in their low-energy spectrum of excitations. This mode, which appears as a pole in the retarded correlators of charge density and longitudinal currents, has some characteristics similar to that of the zero sound in Fermi liquids. Given some reasonable assumptions, we argue that the class of theories with $\theta =d-1$ that logarithmically violate the area law in the entanglement entropy in a manner reminiscent of theories with Fermi surfaces does not exhibit a zero-sound-like mode in the low-energy spectrum of the probe sector. Furthermore, utilizing the holographic Wilsonian approach, we explicitly show that such a mode has a natural interpretation as a Goldstone boson arising from the spontaneous breaking of a specific symmetry.

If moduli, or other long-lived heavy states, decay in the early universe in part into light and feebly interacting particles (such as axions), these decay products could account for the additional energy density in radiation that is suggested by recent measurements of the cosmic microwave background. These moduli decays will also, however, alter the thermal history of the early universe, potentially reducing the thermal relic abundance of dark matter. If this is the case, then dark matter particles must annihilate with an even lower cross section than required in the standard thermal scenario ($⟨\sigma v⟩\ll 3\times {10}^{-26}{\mathrm{cm}}^3/\mathrm{s}$) if they are to make up the observed density of dark matter. This possibility has significant implications for direct and indirect searches for dark matter.

Models of cosmological scalar fields often feature “attractor solutions” to which the system evolves for a wide range of initial conditions. There is some tension between this well-known fact and another well-known fact: Liouville’s theorem forbids true attractor behavior in a Hamiltonian system. In universes with vanishing spatial curvature, the field variables $\varphi$ and $\dot{\varphi }$ specify the system completely, defining an effective phase space. We investigate whether one can define a unique conserved measure on this effective phase space, showing that it exists for $m^2{\varphi }^2$ potentials and deriving conditions for its existence in more general theories. We show that apparent attractors are places where this conserved measure diverges in the $\varphi \mathrm{\text{−}}\dot{\varphi }$ variables and suggest a physical understanding of attractor behavior that is compatible with Liouville’s theorem.

The reconstruction of the cosmic microwave background lensing potential is based on a Taylor expansion of lensing effects which is known to have poor convergence properties. For lensing of temperature fluctuations, an understanding of the higher order terms in this expansion which is accurate enough for current experimental sensitivity levels has been developed in Hanson et al. (2010), as well as a slightly modified Hu and Okamoto quadratic estimator which incorporates lensed rather than unlensed spectra into the estimator weights to mitigate the effect of higher order terms. We extend these results in several ways: (1) we generalize this analysis to the full set of quadratic temperature/polarization lensing estimators, (2) we study the effect of higher order terms for more futuristic experimental noise levels, (3) we show that the ability of the modified quadratic estimator to mitigate the effect of higher order terms relies on a delicate cancellation which occurs only when the true lensed spectra are known. We investigate the sensitivity of this cancellation to uncertainties in or knowledge of these spectra. We find that higher order terms in the Taylor expansion can impact projected error bars at experimental sensitivities similar to those found in future ACTpol/SPTpol experiments.

Using data from the Fermi Gamma-Ray Space Telescope, a spatially extended component of gamma rays has been identified from the direction of the Galactic center, peaking at energies of $\sim 2–3\mathrm{GeV}$. More recently, it has been shown that this signal is not confined to the innermost hundreds of parsecs of the Galaxy, but instead extends to at least $\sim 3\mathrm{kpc}$ from the Galactic center. While the spectrum, intensity, and angular distribution of this signal is in good agreement with predictions from annihilating dark matter, it has also been suggested that a population of unresolved millisecond pulsars could be responsible for this excess GeV emission from the inner Galaxy. In this paper, we consider this later possibility in detail. Comparing the observed spectral shape of the inner Galaxy’s GeV excess to the spectrum measured from 37 millisecond pulsars by Fermi, we find that these sources exhibit a spectral shape that is much too soft at sub-GeV energies to accommodate this signal. We also construct population models to describe the spatial distribution and luminosity function of the Milky Way’s millisecond pulsars. After taking into account constraints from the observed distribution of Fermi sources (including both sources known to be millisecond pulsars, and unidentified sources which could be pulsars), we find that millisecond pulsars can account for no more than $\sim 10\%$ of the inner Galaxy’s GeV excess. Each of these arguments strongly disfavor millisecond pulsars as the source of this signal.