We obtain constraints on parameters of the Yukawa-type corrections to Newton’s gravitational law from measurements of the gradient of the Casimir force between surfaces coated with ferromagnetic metal Ni and from measurements of the Casimir force between Au-coated sinusoidally corrugated surfaces at various angles between corrugations. It is shown that constraints following from the experiment with magnetic surfaces are slightly weaker than currently available strongest constraints but benefit from increased reliability and independence of systematic effects. The constraints derived from the experiment with corrugated surfaces within the interaction region from 11.6 to 29.2 nm are stronger up to a factor of 4 than the strongest constraints derived from other experiments. The possibility of further strengthening of constraints on non-Newtonian gravity by using the configurations with corrugated boundaries is proposed.

We briefly review two recently developed extensions of the Lorentzian geometry of spacetime and prove that they are in fact closely related. The first is the concept of observer space, which generalizes the space of Lorentzian observers, i.e., future unit timelike vectors, using Cartan geometry. The second is the concept of Finsler spacetimes, which generalizes the Lorentzian metric of general relativity to an observer-dependent Finsler metric. We show that every Finsler spacetime possesses a well-defined observer space that can naturally be equipped with a Cartan geometry. Conversely, we derive conditions under which a Cartan geometry on observer space gives rise to a Finsler spacetime. We further show that these two constructions complement each other. We finally apply our constructions to two gravity theories, MacDowell-Mansouri gravity on observer space and Finsler gravity, and translate their actions from one geometry to the other.

We show that results from the Planck satellite reported in 2013 are consistent with cyclic models of the Universe for natural parameter ranges (i.e. order unity dimensionless coefficients), assuming the standard entropic mechanism for generating curvature perturbations. With improved precision, forthcoming results from Planck and other experiments should be able to test the remaining parameter range and confirm or refute the core predictions, i.e. no observable primordial $B$-mode polarization and detectable local non-Gaussianity. A new prediction, given the Planck 2013 constraints on the bispectrum, is a sharp constraint on the local trispectrum parameter $g_{NL}$; namely, the currently best-understood models predict it is negative, with $g_{NL}\lesssim -1700$.

One of the most ambitious goals of gravitational-wave astronomy is to observe the stochastic gravitational-wave background. Correlated noise in two or more detectors can introduce a systematic error, which limits the sensitivity of stochastic searches. We report on measurements of correlated magnetic noise from Schumann resonances at the widely separated LIGO and Virgo detectors. We investigate the effect of this noise on a global network of gravitational-wave detectors and derive a constraint on the allowable coupling of environmental magnetic fields to test mass motion in gravitational-wave detectors. We find that while correlated noise from global electromagnetic fields could be safely ignored for initial LIGO stochastic searches, it could severely impact Advanced LIGO, Advanced Virgo, KAGRA, as well as third-generation detectors.

We propose a robust, unified framework, in which the similar baryon and dark matter cosmic abundances both arise from the physics of weakly interacting massive particles (WIMPs), with the rough quantitative success of the so-called “WIMP miracle.” In particular the baryon asymmetry arises from the decay of a metastable WIMP after its thermal freeze-out at or below the weak scale. A minimal model and its embedding in $R$-parity violating supersymmetry are studied as examples. The new mechanism saves $R$-parity violating supersymmetry from the potential crisis of washing out primordial baryon asymmetry. Phenomenological implications for the LHC and precision tests are discussed.

We present a lattice QCD calculation of the $\Delta (1232)$ matrix elements of the axial-vector and pseudoscalar currents. The decomposition of these matrix elements into the appropriate Lorentz invariant form factors is carried out, and the techniques to calculate the form factors are developed and tested using quenched configurations. Results are obtained for $2+1$ domain wall fermions and within a hybrid scheme with domain wall valence and staggered sea quarks. Two Goldberger-Treiman–type relations connecting the axial to the pseudoscalar effective couplings are derived. These and further relations based on the pion-pole dominance hypothesis are examined using the lattice QCD results, finding support for their validity. Using lattice QCD results on the axial charges of the nucleon and the $\Delta$, as well as the nucleon-to-$\Delta$ transition coupling constant, we perform a combined chiral fit to all three quantities and study their pion mass dependence as the chiral limit is approached.

We study the properties of the covariant supersymmetric and $\kappa$-symmetric action for a system of N nearly coincident M0-branes (mM0 system) in flat 11-dimensional (11D) superspace and obtain supersymmetric equations for this dynamical system. Although a single M0-brane is the massless 11D superparticle, center-of-energy motion of the mM0 system is characterized by a non-negative constant mass $M$ constructed from the matrix fields describing the relative motion of mM0 constituents. We show that a bosonic solution of the mM0 equations can be supersymmetric iff this effective mass vanishes, $M^2=0$, and that all the supersymmetric bosonic solutions preserve just one half of the 11D supersymmetry.

We explore the cosmological implications of a mechanism found in several approaches to quantum gravity, whereby the spectral dimension of spacetime runs from the standard value of 4 in the infrared (IR) to a smaller value in the ultraviolet (UV). Specifically, we invoke the picture where the phenomenon is associated with modified dispersion relations. With minimal assumptions, we find that UV behavior leading to 2 spectral dimensions results in an exactly scale-invariant spectrum of vacuum scalar and tensor fluctuations, regardless of the equation of state. The fluctuation production mechanism is analogous to the one known for varying speed of sound/light models and, unlike in inflation, the spectrum is already scale invariant before leaving the horizon, remaining so after freeze-in. In the light of Planck’s recent results we also discuss scenarios that break exact scale invariance, such as the possibility that the spectral dimension runs down to a value slightly higher than 2, or runs down to 2 but with an extremely slow transient. We further show that the tensor to scalar ratio is fixed by the UV ratio between the speed of gravity and the speed of light. Not only does our model not require inflation, but at its most minimal it seems incompatible with it. In contrast, we find that running spectral dimensions can improve the outlook of the cyclic/ekpyrotic scenario, solving the main problems present in its simplest and most appealing realizations.

Self-interacting dark matter resolves the issue of cuspy profiles that appear in noninteracting cold dark matter simulations; it may additionally resolve the so-called “too big to fail” problem in structure formation. Asymmetric dark matter provides a natural explanation of the comparable densities of baryonic matter and dark matter. In this paper, we discuss unique indirect detection signals produced by a minimal model of self-interacting asymmetric scalar dark matter. Through the formation of dark matter bound states, a dark force mediator particle may be emitted; the decay of this particle may produce an observable signal. We estimate the produced signal and explicitly demonstrate parameters for which the signal exceeds current observations.

It was shown recently that the original SU(5) theory of Georgi and Glashow, augmented with an adjoint fermionic multiplet ${24}_F$, can be made compatible both with neutrino masses and gauge coupling unification. In particular, the model predicts that either electroweak-triplet states are light, within the reach of the Large Hadron Collider (LHC), or proton decay will become accessible at the next generation of megaton-scale facilities. In this paper, we present the computation of the correlation function between the electroweak-triplet masses and the unification scale at the next-to-next-to-leading order. Such an accuracy on the theory side is necessary in order to settle the convergence of the perturbative expansion and to match the experimental precision on the determination of the electroweak gauge couplings at the $Z$-boson mass scale.

We propose a simple renormalizable model for the spontaneous $CP$ violation based on $\mathrm{SU}(2{)}_L\times \mathrm{U}(1{)}_Y\times A_4$ symmetry in a radiative seesaw mechanism, which can be guaranteed by an extra $Z_2$ symmetry. In our model $CP$ is spontaneously broken at high energies, after the breaking of flavor symmetry, by a complex vacuum expectation value of the $A_4$ triplet and gauge-singlet scalar field. We show that the spontaneously generated $CP$ phase could become a natural source of leptogenesis, and also investigate $CP$ violation at low energies in the lepton sector and show how the $CP$ phases in the Pontecorvo-Maki-Nakagawa-Sakata formalism could arise through a spontaneous symmetry-breaking mechanism. As a numerical study, interestingly, we show that the normal mass hierarchy favors relatively large values of ${\theta }_{13}$, large deviations from maximality of ${\theta }_{23}<\pi /4$, and the Dirac-$CP$ phase $0°\le {\delta }_{CP}\le 50°$ and $300°\le {\delta }_{CP}\le 360°$. For the inverted hierarchy case, the experimentally measured values of ${\theta }_{13}$ favors ${\theta }_{23}>\pi /4$ and discrete values of ${\delta }_{CP}$ around 100°, 135°, 255°, and 300°. Finally, with a successful leptogenesis our numerical results give more predictive values on the Dirac $CP$ phase: for the normal mass hierarchy $1°\lesssim {\delta }_{CP}\lesssim 10°$ and for inverted one ${\delta }_{CP}\sim 100°$, 135°, 300°.

We propose a new model of leptons and quarks based on the discrete flavor symmetry $T^{\prime }$, the double covering of $A_4$, in which the hierarchies of charged fermion masses and the mildness of neutrino masses are responsible for Higgs scalars. After spontaneous breaking of flavor symmetry, with the constraint of renormalizability in the Lagrangian, the leptons have $m_e=0$ and the quarks have the Cabibbo-Kobayashi-Maskawa mixing angles ${\theta }_{12}^q=13°$, ${\theta }_{23}^q=0°$ and ${\theta }_{13}^q=0°$. Thus, certain effective dimension-5 operators are introduced, which induce $m_e\ne 0$ and lead the quark mixing matrix to the Cabibbo-Kobayashi-Maskawa one in the form. On the other hand, the neutrino Lagrangian still keeps renormalizability. For completeness, we show a numerical analysis: in the lepton sector, only normal mass hierarchy is permitted within $3\sigma$ experimental bounds with the prediction of both large deviations from maximality in the atmospheric mixing angle ${\theta }_{23}$ and the measured values of the reactor angle. So, future precise measurements of ${\theta }_{23}$, whether ${\theta }_{23}\to 45°$ or $|{\theta }_{23}-45°|\to 5°$, will either exclude or favor our model. Together with it, our model makes predictions for the Dirac $CP$ phase, which is almost compatible with the global analysis in $1\sigma$ experimental bounds. Moreover, we show the effective mass $|m_{ee}|$ measurable in neutrinoless double beta decay to be in the range $0.04\lesssim |m_{ee}|[\mathrm{eV}]<0.11$, which can be tested in near future neutrino experiments.

We construct a general class of exact regular black hole solutions with toroidal horizon topology in five-dimensional anti–de Sitter gravity with a self-interacting scalar field. With these boundary conditions and due to the nontrivial backreaction of the scalar field, the no-hair theorems can be evaded so that an event horizon can be formed. The scalar field is regular everywhere outside the curvature singularity and it vanishes at the boundary where the potential is finite. We study the properties of these black holes in the context of AdS/CFT duality and comment on the dual operators, which saturate the unitarity bound. We present exact expressions for the beta function and construct a $c$-function that characterizes the renormalization-group flow.

In the gravitational context, Liouville theory is the two-dimensional conformal field theory that controls the boundary dynamics of asymptotically ${\mathrm{AdS}}_3$ spacetimes at the classical level. By taking a suitable limit of the coupling constants of the Hamiltonian formulation of Liouville, we construct and analyze a ${\mathrm{BMS}}_3$ invariant two-dimensional field theory that is likely to control the boundary dynamics at null infinity of threedimensional asymptotically flat gravity.

Gravitational perturbations of flat Minkowski space make the Rindler horizon dynamical: the horizon satisfies mechanical laws analogous to the ones followed by black holes. We describe the gravitational perturbation of Minkowski space using perturbative field-theoretical methods. The change in the area of the Rindler horizon is described in terms of the deflection of light rays by the gravitational field. The difference between the area of the perturbed and the unperturbed horizon is related to the energy of matter crossing the horizon. We derive consistency conditions for the validity of our approximations and compare our results to similar ones present in the literature. Finally, we discuss how this setting can be used in perturbative quantum gravity to extend the classical mechanical laws to thermodynamic laws, with the entanglement of field modes across the Rindler horizon providing a notion of thermodynamic entropy.

The motion of charged test particles in the gravitational field of a rotating and electromagnetically charged black hole as described by the Kerr-Newman metric is considered. We completely classify the colatitudinal and radial motion on the extended manifold $-\infty \le r\le \infty$, including orbits crossing the horizons or $r=0$. Analytical solutions of the equations of motion in terms of elliptic functions are presented which are valid for all types of orbits.

Conversion of the cosmic microwave background (CMB) photons into gravitational waves at the post recombination epoch is considered. We calculate the probability of transformation of the CMB photons into gravitons in the presence of a large scale magnetic field. Based on the present day limits on the strength of the large scale magnetic field, we show that the probability of the produced gravitons as a result of photon to graviton conversion is reasonable and such a mechanism would produce an isotropic background of gravitational waves in the same frequency range of the CMB photons. The mechanism proposed would be another good opportunity to study the high frequency part of the spectrum of gravitational waves.

Many approaches to quantum gravity have resorted to diffusion processes to characterize the spectral properties of the resulting quantum spacetimes. We critically discuss these quantum-improved diffusion equations and point out that a crucial property, namely positivity of their solutions, is not preserved automatically. We then construct a novel set of diffusion equations with positive semidefinite probability densities, applicable to asymptotically safe gravity, Hořava-Lifshitz gravity and loop quantum gravity. These recover all previous results on the spectral dimension and shed further light on the structure of the quantum spacetimes by assessing the underlying stochastic processes. Pointing out that manifestly different diffusion processes lead to the same spectral dimension, we propose the probability distribution of the diffusion process as a refined probe of quantum spacetime.

The abundance of lithium-7 confronts cosmology with a long lasting problem between the predictions of standard big bang nucleosynthesis and the baryonic density determined from the cosmic microwave background observations. This article investigates the influence of the existence of a mirror world, focusing on models in which neutrons can oscillate into mirror neutrons. Such a mechanism allows for an effective late time neutron injection, which induces an increase of the destruction of beryllium-7, due to an increase of the neutron capture, and then a decrease of the final lithium-7 abundance. Big bang nucleosynthesis sets constraints on the oscillation time between the two types of neutrons and the possibility for such a mechanism to solve, or alleviate, the lithium problem is emphasized.

We demonstrate that a wide range of viable $f(R)$ parametrizations (including the Hu and Sawicki and the Starobinsky models) can be expressed as perturbations deviating from the $\Lambda \mathrm{CDM}$ Lagrangian. We constrain the deviation parameter $b$ using a combination of geometrical and dynamical observational probes. In particular, we perform a joint likelihood analysis of the recent type Ia supernova data, the cosmic microwave background shift parameters, the baryonic acoustic oscillations and the growth rate data provided by the various galaxy surveys. This analysis provides constraints for the following parameters: the matter density ${\Omega }_{m0}$, the deviation from $\Lambda \mathrm{CDM}$ parameter $b$ and the growth index $\gamma (z)$. We parametrize the growth index $\gamma (z)$ in three manners (constant, Taylor expansion around $z=0$, and Taylor expansion around the scale factor). We point out the numerical difficulty for solving the generalized $f(R)$ Friedmann equation at high redshifts due to the stiffness of the resulting ordinary differential equation. We resolve this problem by constructing an efficient analytical perturbative method in the deviation parameter $b$. We demonstrate that this method is highly accurate, by comparing the resulting analytical expressions for the Hubble parameter with the numerical solutions at low and intermediate redshifts. Surprisingly, despite its perturbative nature, the accuracy of the method persists even for values of $b$ that are of $O(1)$.