Generic extensions of the Standard Model that respect baryon and lepton numbers have accidentally stable particles. Typical examples are the lightest exotic neutral fermion, or “neutralino,” and fields with nontrivial lepton and baryon charges. In this paper we identify the accidentally stable neutralino with the dark matter, and discuss its phenomenology in the framework of warped extra dimensions. We find that annihilation into other Kaluza-Klein resonances is often allowed and very efficient. The observed dark matter abundance may then be obtained with couplings of order unity and a compactification scale above the TeV. Light dark matter is also possible in the presence of unsuppressed couplings to the Higgs boson. In this latter case dark matter direct detection experiments will soon be able to probe a significant portion of the parameter space. This analysis suggests that dark matter is a natural feature of realistic models with warped extra dimensions.

We present results about the effect of the use of a stiffer equation of state, namely the ideal-fluid $\mathrm{\Gamma }=2.75$ one, on the dynamical bar-mode instability in rapidly rotating polytropic models of neutron stars in full general relativity. We determine the change on the critical value of the instability parameter $\beta$ for the emergence of the instability when the adiabatic index $\mathrm{\Gamma }$ is changed from 2 to 2.75 in order to mimic the behavior of a realistic equation of state. In particular, we show that the threshold for the onset of the bar-mode instability is reduced by this change in the stiffness and give a precise quantification of the change in value of the critical parameter ${\beta }_c$. We also extend the analysis to lower values of $\beta$ and show that low-beta shear instabilities are present also in the case of matter described by a simple polytropic equation of state.

The dynamical generation of wormholes within an extension of General Relativity (GR) containing (Planck’s scale-suppressed) Ricci-squared terms is considered. The theory is formulated assuming the metric and connection to be independent (Palatini formalism) and is probed using a charged null fluid as a matter source. This has the following effect: starting from Minkowski space, when the flux is active the metric becomes a charged Vaidya-type one, and once the flux is switched off the metric settles down into a static configuration such that far from the Planck scale the geometry is virtually indistinguishable from that of the standard Reissner-Nordström solution of GR. However, the innermost region undergoes significant changes, as the GR singularity is generically replaced by a wormhole structure. Such a structure becomes completely regular for a certain charge-to-mass ratio. Moreover, the nontrivial topology of the wormhole allows us to define a charge in terms of lines of force trapped in the topology such that the density of lines flowing across the wormhole throat becomes a universal constant. In light of our results, we comment on the physical significance of curvature divergences in this theory and the topology change issue, which support the view that space-time could have a foamlike microstructure pervaded by wormholes generated by quantum gravitational effects.

We derive a noncovariant but simple representation for the self-energy of a conformally transformed graviton field on the cosmological patch of de Sitter. Our representation involves four structure functions, as opposed to the two that would be necessary for a manifestly de Sitter invariant representation. We work out what the four structure functions are for the one loop correction due to a massless, minimally coupled scalar and we employ the result to work out what happens to dynamical gravitons.

Quantum inequalities are bounds on negative time averages of the energy density of a quantum field. They can be used to rule out exotic spacetimes in general relativity. We study quantum inequalities for a scalar field with a background potential (i.e., a mass that varies with spacetime position) in Minkowski space. We treat the potential as a perturbation and explicitly calculate the first-order correction to a quantum inequality with an arbitrary sampling function, using general results of Fewster and Smith. For an arbitrary potential, we give bounds on the correction in terms of the maximum values of the potential and its first three derivatives. The techniques we develop here will also be applicable to quantum inequalities in general spacetimes with small curvature, which are necessary to rule out exotic phenomena.

In the Einstein frame picture of Starobinky’s $R^2$ inflation model, cosmic inflation is driven by a slowly rolling inflaton field, called a scalaron, and followed by a coherently oscillating scalaron phase. Since the scalaron oscillates excessively many times in its potential, which has a quadratic minimum and is a little shallower than quadratic on the positive side, it may fragment into long-living localized objects, called oscillons or I balls, due to nonlinear growth of fluctuations before reheating of the Universe. We show that, while parametric self-resonances amplify scalaron fluctuations in the Minkowski background, the growth cannot overcome the decay due to expansion in the Friedmann background after $R^2$ inflation. By taking into account the backreaction from the metric of spacetime, modes that are larger than a critical scale are indeed amplified and become nondecaying. However, those nondecaying modes are not growing enough to form spatially localized lumps of the scalaron. Thus, reheating processes are unaltered by oscillons/I balls, and they proceed through perturbative decay of the scalaron as studied in the original work.

Effective field theory provides a perturbative framework to study the evolution of cosmological large-scale structure. We investigate the underpinnings of this approach, and suggest new ways to compute correlation functions of cosmological observables. We find that, in contrast with quantum field theory, the appropriate effective theory of classical cosmological perturbations involves interactions that are nonlocal in time. We describe an alternative to the usual approach of smoothing the perturbations, based on a path-integral formulation of the renormalization group equations. This technique allows for improved handling of short-distance modes that are perturbatively generated by long-distance interactions.

One of the key science goals of advanced gravitational-wave detectors is to observe a stochastic gravitational-wave background. However, recent work demonstrates that correlated magnetic fields from Schumann resonances can produce correlated strain noise over global distances, potentially limiting the sensitivity of stochastic background searches with advanced detectors. In this paper, we estimate the correlated noise budget for the worldwide advanced detector network and conclude that correlated noise may affect upcoming measurements. We investigate the possibility of a Wiener filtering scheme to subtract correlated noise from Advanced LIGO searches, and estimate the required specifications. We also consider the possibility that residual correlated noise remains following subtraction, and we devise an optimal strategy for measuring astronomical parameters in the presence of correlated noise. Using this new formalism, we estimate the loss of sensitivity for a broadband, isotropic stochastic background search using 1 yr of LIGO data at design sensitivity. Given our current noise budget, the uncertainty with which LIGO can estimate energy density will likely increase by a factor of $\approx 12$—if it is impossible to achieve significant subtraction. Additionally, narrow band cross-correlation searches may be severely affected at low frequencies $f\lesssim 70\mathrm{Hz}$ without effective subtraction.

We test the FLRW cosmology by reconstructing in a model-independent way both the Hubble parameter $H(z)$ and the comoving distance $D(z)$ via the most recent Hubble and Supernovae Ia data. In particular we use data binning with direct error propagation, the principal component analysis, the genetic algorithms and the Padé approximation. Using our reconstructions we evaluate the Clarkson et al. test known as ${\mathrm{\Omega }}_K(z)$, whose value is constant in redshift for the standard cosmological model, but deviates otherwise. Using present data, we find good agreement with the expected values of the standard cosmological model within the experimental errors, which are, however, large enough to allow for alternative cosmologies. A discrimination between the models may be possible for more precise future data. Finally, we provide forecasts, exploiting the baryon acoustic oscillation measurements from the Euclid survey.

The motion of x-ray and gamma-ray pulses in the magnetic field of the pulsar, taking into account the nonlinearity of electrodynamics in a vacuum, is calculated. It is shown that in these conditions, each pulse propagates in the form of two orthogonally polarized normal waves with different speeds. The propagation time from the common source in the pulsars’ magnetosphere to a remote observer is calculated for each mode. An experiment to measure the delay time of one pulse with respect to the other is proposed.

The IceCube Collaboration has recently reported evidence for a high-energy extraterrestrial neutrino flux. During two years of operation 28 events with energies between 30 TeV and 1.2 PeV were observed while only 10.6 events were expected from conventional atmospheric backgrounds. The hadronic interactions responsible for this IceCube excess will also produce a flux of high-energy $\gamma$-rays that can serve as a probe of source direction and distance. We show that existing TeV to PeV diffuse $\gamma$-ray limits support the interpretation that the IceCube excess is mostly of extragalactic origin. However, we point out that $\gamma$-ray surveys are biased in the Northern Hemisphere whereas the recent IceCube data tentatively show a weak preference for the Southern Sky. Possible sub-dominant contributions from Galactic neutrino sources like remnants of supernovae and hypernovae are marginally consistent with present $\gamma$-ray limits. This emphasizes the importance of future diffuse TeV to PeV $\gamma$-ray surveys in the Southern Hemisphere, particularly in the extended region around the Galactic center including the Fermi Bubbles.

Effective weakly interacting massive particle (WIMP) models are minimal extensions of the standard model that explain the relic density of dark matter by the “WIMP miracle.” In this paper we consider the phenomenology of effective WIMPs with trilinear couplings to leptons and a new “lepton partner” particle. The observed relic abundance fixes the strength of the cubic coupling, so the parameters of the models are defined by the masses of the WIMP and lepton partner particles. This gives a simple parameter space where collider and direct detection experiments can be compared under well-defined physical minimality assumptions. The most sensitive collider probe is the search for $\text{leptons}+\mathrm{MET}$, while the most sensitive direct detection channel is scattering from nuclei arising from loop diagrams. Collider and direct detection searches are highly complementary: colliders give the only meaningful constraint when dark matter is its own antiparticle, while direct detection is generally more sensitive if the dark matter is not its own antiparticle.

The ${\mathrm{\Lambda }}_c(2286)N$ system is studied in a chiral constituent quark model, and the resulting $s$-wave interaction is used in separable form within three-body models of the $\pi {\mathrm{\Lambda }}_{c}N$ system with quantum numbers $(C,I,J^P)=(+1,\frac{3}{2},2^{+})$. Separable interactions are also used for the dominant $p$-wave pion-baryon channels dominated by the $\mathrm{\Delta }(1232)$ and ${\mathrm{\Sigma }}_c(2520)$ resonances. Faddeev equations with relativistic kinematics are solved on the real axis to search for bound states and in the complex plane to search for three-body resonances. Some of the models considered generate a very narrow bound state, requiring isospin violation for its strong decay. Other models lead to a narrow resonance ($\mathrm{\Gamma }\lesssim 0.4\mathrm{MeV}$) for a resonance mass below the ${\mathrm{\Sigma }}_c(2455)N$ threshold. This would be the lowest-lying $C=+1$ dibaryon, with mass estimated as $\approx 3370\pm 15\mathrm{MeV}$.

We argue that the perturbative QCD correlations contribute dominantly to the double parton distributions as compared to the nonperturbative ones in the limit of sufficiently large hard scales and the not parametrically small longitudinal momentum fractions.

In the Standard Model, the Higgs coupling to gluons is almost entirely induced by top quark loops. We derive the logarithmic structure of Higgs production in association with two jets. Just like in the one-jet case, the transverse momentum distributions exhibit logarithms of the top quark mass and can be used to test the nature of the loop–induced Higgs coupling to gluons. Using Higgs decays to W bosons and to tau leptons, we show how the corresponding analyses hugely benefit from the second jet in the relevant signal rate as well as in the background rejection.

The nonlinear Breit-Wheeler process of electron-positron pair production off a probe photon colliding with a low-frequency and a high-frequency electromagnetic wave that propagate in the same direction is analyzed. We calculate the pair-production probability and the spectra of the created pair in the nonlinear Breit-Wheeler processes of pair production off a probe photon colliding with two plane waves or one of these two plane waves. The differences of these two cases are discussed. We evidently show, in the two-wave case, the possibility of Breit-Wheeler pair production with simultaneous photon emission into the low-frequency wave and the high multiphoton phenomena: (i) Breit-Wheeler pair production by absorption of the probe photon and a large number of photons from the low-frequency wave, in addition to the absorption of one photon from the high-frequency wave; (ii) Breit-Wheeler pair production by absorption of the probe photon and one photon from the high-frequency wave with simultaneous emission of a large number of photons into the low-frequency wave. The phenomenon of photon emission into the wave cannot happen in the one-wave case. Compared with the one-wave case, the contributions from high multiphoton processes are largely enhanced in the two-wave case. The results presented in this article show a possible way to access the observations of the phenomenon of photon emission into the wave and high multiphoton phenomenon in Breit-Wheeler pair production even with the laser-beam intensity of order ${10}^{18}\mathrm{W}/{\mathrm{cm}}^2$.

In Phys. Rev. D 84, 024020 (2011) Harko, Lobo, Nojiri and Odintsov presented a modified theory of gravitation, $f(R,T)$ gravity, where the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar and of the trace of the stress-energy tensor. In this Comment we correct the conservation equation of the stress-energy tensor, since we noticed that the authors missed an essential term which has consequences in the equation of motion of test particles. We thus correct the derivation of this equation of motion and comment on some of its consequences.

We investigate the real-time dynamics of U(1) and SU(N) gauge theories coupled to fermions on a lattice. While real-time lattice gauge theory is not amenable to standard importance sampling techniques, for a large class of time-dependent problems the quantum dynamics can be accurately mapped onto a classical-statistical ensemble. We illustrate the genuine quantum contributions included in this description by giving a diagrammatic representation in a series expansion. The nonperturbative simulation method is then applied to electron-positron production in quantum electrodynamics in three spatial dimensions. We compare to analytic results for constant background field and demonstrate the importance of backreaction of the produced fermion pairs on the gauge fields.

We calculate the quantum corrections to the two-point function of four-dimensional topologically massive non-Abelian vector fields at one-loop order for $SU(N)$ gauge theory in Feynman–’t Hooft gauge. We calculate the beta function of the gauge coupling constant and find that the theory becomes asymptotically free faster than pure $SU(N)$ gauge theory.

We investigate the asymptotic behavior of peculiar velocities in certain physically significant time-dependent gravitational fields. Previous studies of the motion of free test particles have focused on the collapse scenario, according to which a double-jet pattern with Lorentz factor $\gamma \to \infty$ develops asymptotically along the direction of complete gravitational collapse. In the present work, we identify a second wave scenario, in which a single-jet pattern with Lorentz factor $\gamma \to \infty$ develops asymptotically along the direction of wave propagation. The possibility of a connection between the two scenarios for the formation of cosmic jets is critically examined.