Is it possible to detect a new weakly coupled force at the QCD scale that interacts primarily with quarks? This work investigates experimental signatures of a new MeV–GeV gauge boson that couples to the baryon number, with attention to the 100 MeV–GeV mass range that is the regime of nonperturbative QCD. Such a state can be searched for in rare radiative decays of light mesons ($\eta ,{\eta }^{\prime },\varphi ,\omega$) as a ${\pi }^0\gamma$ resonance, which is its leading decay mode from 140 to 620 MeV. This is a new discovery window for forces beyond the Standard Model that is not covered by existing dark photon searches.

We study the thermalization process in highly occupied non-Abelian plasmas at weak coupling. The nonequilibrium dynamics of such systems is classical in nature and can be simulated with real-time lattice gauge theory techniques. We provide a detailed discussion of this framework and elaborate on the results reported in J. Berges, K. Boguslavski, S. Schlichting, and R. Venugopalan, Phys. Rev. D 89, 074011 (2014) along with novel findings. We demonstrate the emergence of universal attractor solutions, which govern the nonequilibrium evolution on large time scales both for nonexpanding and expanding non-Abelian plasmas. The turbulent attractor for a nonexpanding plasma drives the system close to thermal equilibrium on a time scale $t\sim Q^{-1}{\alpha }_s^{-7/4}$. The attractor solution for an expanding non-Abelian plasma leads to a strongly interacting albeit highly anisotropic system at the transition to the low-occupancy or quantum regime. This evolution in the classical regime is, within the uncertainties of our simulations, consistent with the “bottom up” thermalization scenario [R. Baier, A. H. Mueller, D. Schiff, and D. T. Son, Phys. Lett. B 502, 51 (2001)]. While the focus of this paper is to understand the nonequilibrium dynamics in weak coupling asymptotics, we also discuss the relevance of our results for larger couplings in the early time dynamics of heavy ion collision experiments.

We study the transverse single-spin asymmetry for single-hadron production in proton-proton collisions within the framework of collinear twist-3 factorization in quantum chromodynamics. By taking into account the contribution due to parton fragmentation, we obtain a very good description of all high transverse-momentum data for neutral and charged pion production from the Relativistic Heavy Ion Collider. Our study may provide the crucial step toward a final solution to the long-standing problem of what causes transverse single-spin asymmetries in hadronic collisions within quantum chromodynamics. We show for the first time that it is possible to simultaneously describe spin/azimuthal asymmetries in proton-proton collisions, semi-inclusive deep-inelastic scattering, and electron-positron annihilation by using collinear twist-3 factorization in the first process along with transverse-momentum-dependent functions extracted from the latter two reactions.

For an evaporating black hole which is a radiation-black hole combined system, we express the entanglement entropy and the Page time in terms of the conformal time in the Russo-Susskind-Thorlacius model. The entropy change of the black hole is nicely written in terms of Hawking flux. Integrating the first law of thermodynamics, we can obtain the decreasing black hole entropy and the increasing radiation entropy, and the entanglement entropy for this system based on the Page argument. We also obtain analytically the critical temperature to release black hole information, which corresponds to the Page time, and discuss the relation between the conserved total entropy and information recovering of the black hole in this model.

Vacuum birefringence is governed by the amplitude for a photon to flip helicity or polarization state in an external field. Here, we calculate the flip and nonflip amplitudes in arbitrary plane wave backgrounds, along with the induced spacetime-dependent refractive indices of the vacuum. We compare the behavior of the amplitudes in the low energy and high energy regimes, and analyze the impact of pulse shape and energy. We also provide the first lightfront-QED derivation of the coefficients in the Heisenberg-Euler effective action.

Cosmic superstring loops within the galaxy microlens background point sources lying close to the observer-string line of sight. For suitable alignments, multiple paths coexist and the (achromatic) flux enhancement is a factor of two. We explore this unique type of lensing by numerically solving for geodesics that extend from source to observer as they pass near an oscillating string. We characterize the duration of the flux doubling and the scale of the image splitting. We probe and confirm the existence of a variety of fundamental effects predicted from previous analyses of the static infinite straight string: the deficit angle, the Kaiser-Stebbins effect, and the scale of the impact parameter required to produce microlensing. Our quantitative results for dynamical loops vary by $O(1)$ factors with respect to estimates based on infinite straight strings for a given impact parameter. A number of new features are identified in the computed microlensing solutions. Our results suggest that optical microlensing can offer a new and potentially powerful methodology for searches for superstring loop relics of the inflationary era.

Primary energy spectral models are tested in the energy range of 1–200 PeV using standardized extensive air shower responses from BASJE-MAS, Tibet, GAMMA and KASCADE scintillation shower arrays. Results point toward the two-component origin of observed cosmic ray energy spectra in the knee region consisting of a pulsar component superimposed upon rigidity-dependent power law diffuse Galactic flux. The two-component energy spectral model accounts for both the sharp knee shower spectral phenomenon and observed irregularity of all-particle energy spectrum in the region of 50–100 PeV. Alternatively, tested multipopulation primary energy spectra predicted by nonlinear diffusive shock acceleration models describe observed shower spectra in the knee region provided that the cutoff magnetic rigidities of accelerating particles are $6\pm 0.3$ and $45\pm 2\mathrm{PV}$ for the first two populations, respectively. Both tested spectral models confirm the predominant $H-He$ primary nuclei origin of observed shower spectral knee. The parameters of tested energy spectra are evaluated using solutions of the inverse problem on the basis of the corresponding parameterizations of energy spectra for primary $H$, $He$, $O$-like and $Fe$-like nuclei, standardized shower size spectral responses in the $550–1085\mathrm{g}/{\mathrm{cm}}^2$ atmospheric slant depth range and near vertical muon truncated size spectra detected by the GAMMA array.

A redshifted 21 cm signal from neutral hydrogen is one of the most competitive probes of the epoch of reionization (EoR). Unpolarized 21 cm radiation acquires a certain level of linear polarization during the EoR due to Thompson scattering. This linear polarization, if measured, could probe important information about the EoR. We study the effect of Galactic Faraday rotation in the detection of polarization of 21 cm radiation. The effect of Faraday rotation is strong due to the large wavelength nature of the redshifted 21 cm signal. Thus, an initial E-mode signal carried by 21 cm photons is modified in its entirety. We show that a 99% accuracy on rotation measure data is necessary to recover the initial E-mode signal. We conclude that, given the current status of rotation measure observations, it is not possible to retrieve the initial polarization signal of 21 cm from the EoR. However, future radio observations of pulsar sources may improve the accuracy of the Galactic rotation measure to a high degree, making the reconstruction of the initial 21 cm polarization possible.

Basis light-front quantization (BLFQ) has recently been developed as a promising nonperturbative technique. Using BLFQ, we investigate the generalized parton distributions (GPDs) in a nonperturbative framework for a dressed electron in QED. We evaluate light-front wave functions and carry out overlap calculations to obtain GPDs. We also perform perturbative calculations in the corresponding basis spaces to demonstrate that they compare reasonably with the BLFQ results.

The Standard Model fermion sector is enlarged by either one light singlet vectorlike down-type quark or one light vectorlike lepton doublet, which might be accommodated within a five-dimensional representation of $SU(5)$. At low energies the inclusion of these states affects precisely measured observables in flavor physics, as well as electroweak precision measurements. These experimental results strongly constrain couplings of vectorlike states to the Standard Model particles. Having these bounds, we investigate the impact of vectorlike fermions on the mass matrices for down-type quarks and charged leptons in an $SU(5)$ setting. We find that unitary transformations relating an arbitrary flavor basis to the mass eigenstate basis depend only on three free parameters. Then we discuss the parameter space constrained by low-energy data, assuming vectorlike quark and vectorlike lepton masses to be 800 GeV and 400 GeV, respectively. We demonstrate that these two scenarios generate unique patterns for relevant proton decay widths. A further improvement of experimental bounds on proton decay modes would thus differentiate the allowed parameter space. We finally present two full-fledged $SU(5)$ models that allow for gauge coupling unification with light vectorlike fermions under consideration and discuss their viability.

We describe a new technique to determine the contribution to the anomalous magnetic moment of the muon coming from the hadronic vacuum polarization using lattice QCD. Our method reconstructs the Adler function, using Padé approximants, from its derivatives at $q^2=0$ obtained simply and accurately from time-moments of the vector current-current correlator at zero spatial momentum. We test the method using strange quark correlators on large-volume gluon field configurations that include the effect of up and down (at physical masses), strange and charm quarks in the sea at multiple values of the lattice spacing and multiple volumes and show that 1% accuracy is achievable. For the charm quark contributions we use our previously determined moments with up, down and strange quarks in the sea on very fine lattices. We find the (connected) contribution to the anomalous moment from the strange quark vacuum polarization to be $a_{\mu }^s=53.41(59)\times 10^{-10}$, and from charm to be $a_{\mu }^c=14.42(39)\times 10^{-10}$. These are in good agreement with flavor-separated results from nonlattice methods, given caveats about the comparison. The extension of our method to the light quark contribution and to that from the quark-line disconnected diagram is straightforward.

Single and multiple emission of electroweak gauge bosons and in particular of $W$ bosons is discussed in the parton shower language. Algorithms and observables for the reconstruction of both leptonically and hadronically decaying $W$ bosons inside light quark jets are compared, and they are applied to a study of how emission rates of $W$ bosons in light-jet events at the LHC could be measured.

Extremal planar black holes of four-dimensional Einstein-Maxwell theory with a negative cosmological constant have an ${\mathrm{AdS}}_2\times {\mathbb{R}}^2$ near horizon geometry. We show that this near horizon geometry admits a deformation to a two parameter family of extremal geometries with inhomogeneous, spatially periodic horizons. At a linear level, static inhomogeneous perturbations of ${\mathrm{AdS}}_2\times {\mathbb{R}}^2$ decay towards the horizon and thus appear irrelevant under the holographic renormalization group flow. However we have found numerically that nonlinear effects lead to inhomogeneous near horizon geometries. A consequence of these observations is that an arbitrarily small periodic deformation of the boundary theory at nonzero charge density does not flow to ${\mathrm{AdS}}_2\times {\mathbb{R}}^2$ in the IR, but rather to an inhomogeneous horizon. These results shed light on existing numerical studies of low temperature periodically modulated black holes and also offer a new mechanism for holographic metal-insulator crossovers or transitions.

This work presents a general formalism to analyze a generic bulk scalar field in a multiple warped extra-dimensional model with arbitrary number of extra dimensions. The Kaluza-Klein mass modes along with the self-interaction couplings are determined and the possibility of having lowest lying KK mode masses near TeV scale are discussed. Also some numerical values for low-lying KK modes has been presented showing explicit localization around TeV scale. It is argued that the appearance of large number of closely spaced KK modes with enhanced coupling may prompt possible new signatures in collider physics.

We use unitarity techniques to compute the two-loop nonplanar corrections to the Sudakov form factor and the four-point amplitude in the ABJM theory. We start by reconstructing nonplanar integrals from two-particle cuts in three dimensions. This causes ambiguities due to the one-loop, four-point amplitude being subleading in dimensional regularization. We provide a prescription to circumvent them and show that it leads to the correct results, as checked against the recent Feynman diagram computation. For the amplitude, we point out an alternative basis of integrals, including a nonplanar double box with a numerator inspired by color-kinematics duality. We reproduce the result using a combination thereof with the coefficients fixed by generalized unitarity. For the BLG theory, we propose that this gives the form of the amplitude satisfying color-kinematics duality. Finally, we compute the complete two-loop amplitude of three-dimensional $\mathcal{N}=8$ SYM and the corresponding four-point amplitude in $\mathcal{N}=16$ supergravity as a double copy.

We construct a supersymmetric gauge theory on $S^4\times S^1$. We find a consistent supersymmetry transformation which reduces to the 4D $N=2$ supersymmetry transformation studied by Pestun by the dimensional reduction on $S^1$. We find that there is no analogue of the usual Yang-Mills action except in the 4D limit. We also apply the localization technique to the partition function of the theories.

We describe a wide class of inhomogeneous relativistic solutions that are well approximated on cosmological scales by solutions of Newtonian gravity. Error estimates measuring the difference between the Newtonian and relativistic solutions are given. The solutions presented here unambiguously demonstrate that it is possible for Newtonian gravity to provide a good approximation to general relativity on cosmological scales.

A low-energy perturbation theory is developed from the nonperturbative framework of covariant loop quantum gravity (LQG) by employing the background-field method. The resulting perturbation theory is a two-parameter expansion in the semiclassical and low-energy regime. The two expansion parameters are the large spin and small curvature. The leading-order effective action coincides with the Regge action, which well approximates the Einstein-Hilbert action in the regime. The subleading corrections organized by the two expansion parameters give the modifications of the Regge action in the quantum and high-energy regime from LQG. The perturbation theory developed here shows for the first time that covariant LQG produces the high-curvature corrections to Einstein-Regge gravity. This result means that LQG is not a naive quantization of Einstein gravity; rather, it provides the UV modification. The result of the paper may be viewed as the first step toward understanding the UV completeness of LQG.

Time evolution of a black hole lattice universe with a positive cosmological constant $\mathrm{\Lambda }$ is simulated. The vacuum Einstein equations are numerically solved in a cubic box with a black hole in the center. Periodic boundary conditions on all pairs of opposite faces are imposed. Configurations of marginally trapped surfaces are analyzed. We describe the time evolution of not only black hole horizons, but also cosmological horizons. Defining the effective scale factor by using the area of a surface of the cubic box, we compare it with that in the spatially flat dust dominated Friedmann-Lemaître-Robertson-Walker (FLRW) universe with the same value of $\mathrm{\Lambda }$. It is found that the behavior of the effective scale factor is well approximated by that in the FLRW universe. Our result suggests that local inhomogeneities do not significantly affect the global expansion law of the Universe irrespective of the value of $\mathrm{\Lambda }$.