We derive constraints on corrections to Newtonian gravity of the Yukawa type and light elementary particles from two recently performed measurements of the gradient of the Casimir force. In the first measurement the configuration of two Au surfaces has been used, whereas in the second a nonmagnetic metal Au interacted with a magnetic metal Ni. In these configurations one arrives at different and similar, respectively, theoretical predictions for the Casimir force when the competing theoretical approaches are employed. Nevertheless, we demonstrate that the constraints following from both experiments are in mutual agreement and in line with constraints obtained from earlier measurements. This confirms the reliability of constraints on non-Newtonian gravity obtained from measurements of the Casimir force.

We consider Reissner-Nordström solutions in quasitopological gravity, obtaining exact solutions to the field equations yielding charged quasitopological black holes. We study their thermodynamic behavior over a range of parameters that yield ghost-free and stable space times. We find that a sufficiently negative quasitopological parameter can yield black holes with two horizons, even for zero charge. We discuss the thermodynamic stability for the class of solutions we obtain. We also describe the structure of exact charged solutions to $k$th-order quasitopological gravity.

We investigate the configuration resulting after a collision of gravitational sources in a higher dimensional space with extra dimensions. Evidence is found that as the energy increases, there is a phase transition in the topology of the black object that is being formed: from the black hole to the black string topology. An intuitive mechanism for the way the transition takes place is proposed. The transition occurs at a finite value of the energy where an upper and a lower bound is found. Furthermore, at low energies the compact dimension behaves as an extended one while at high energies the extra dimension seems to decouple. Finally, the implications about the Gregory-Laflamme instability, the implications to the accelerators as well as holographic implications are discussed.

Cosmic microwave background (CMB) polarization encodes information not only on the early universe but also dark energy, neutrino mass, and gravity in the late universe through CMB lensing. Ground-based surveys, such as ACTpol, PolarBear, and SPTpol, significantly complement cosmological constraints from the Planck satellite, strengthening the CMB dark energy figure of merit and neutrino mass constraints by factors of 3–4. This changes the dark energy probe landscape. We evaluate the state of knowledge in 2017 from ongoing experiments including dark energy surveys (supernovae, weak lensing, galaxy clustering), fitting for dynamical dark energy, neutrino mass, and a modified gravitational growth index. Adding a modest strong lensing time delay survey improves those dark energy constraints by a further 32%, and an enhanced low-redshift supernova program improves them by 26%.

We cross correlate the gravitational lensing map extracted from cosmic microwave background measurements by the Wilkinson Microwave Anisotropy Probe with the radio galaxy distribution from the NRAO VLA Sky Survey (NVSS) by using a quadratic estimator technique. We use the full covariance matrix to filter the data, and calculate the cross-power spectra for the lensing-galaxy correlation. We explore the impact of changing the values of cosmological parameters on the lensing reconstruction, and obtain statistical detection significances at $>3\sigma$. The results of all cross correlations pass the curl null test as well as a complementary diagnostic test using the NVSS data in equatorial coordinates. We forecast the potential for Planck and NVSS to constrain the lensing-galaxy cross correlation as well as the galaxy bias. The lensing-galaxy cross-power spectra are found to be Gaussian distributed.

We apply the integrated perturbation theory [T. Matsubara, Phys. Rev. D 83, 083518 (2011)] to evaluate the scale-dependent bias in the presence of primordial non-Gaussianity. The integrated perturbation theory is a general framework of nonlinear perturbation theory, in which a broad class of bias models can be incorporated into perturbative evaluations of biased power spectrum and higher-order polyspectra. Approximations such as the high-peak limit or the peak-background split are not necessary to derive the scale-dependent bias in this framework. Applying the halo approach, previously known formulas are rederived as limiting cases of a general formula in this work, and it is implied that modifications should be made in general situations. Effects of redshift-space distortions are straightforwardly incorporated. It is found that the slope of the scale-dependent bias on large scales is determined only by the behavior of primordial bispectrum in the squeezed limit and is not sensitive to bias models in general. It is the amplitude of scale-dependent bias that is sensitive to the bias models. The effects of redshift-space distortions turn out to be quite small for the monopole component of the power spectrum, while the quadrupole component is proportional to the monopole component on large scales and thus also sensitive to the primordial non-Gaussianity.

We forecast the constraints on modified theories of gravity from the cosmic microwave background (CMB) anisotropies bispectrum that arises from correlations between lensing and the Integrated Sachs-Wolfe effect. In models of modified gravity the evolution of the metric potentials is generally altered and the contribution to the CMB bispectrum signal can differ significantly from the one expected in the standard cosmological model. We adopt a parametrized approach and focus on three different classes of models: Linder’s growth index, Chameleon-type models, and $f(R)$ theories. We show that the constraints on the parameters of the models will significantly improve with future CMB bispectrum measurements.

In this paper we study gravitational lensing in the strong field limit from the perspective of cosmic censorship, to investigate whether or not naked singularities, if they exist in nature at all, can be distinguished from black holes. The spacetime we explore from this perspective is the Joshi-Malafarina-Narayan (JMN) metric which represents a spherically symmetric solution to the Einstein field equations with anisotropic pressure and contains a naked singularity at the center. JMN geometry is matched with the Schwarzschild metric to the exterior at a finite radius. This metric was recently shown to be a possible end state of gravitational collapse of a fluid with zero radial pressure. In the presence of the photon sphere, gravitational lensing signature of this spacetime is identical to that of the Schwarzschild black hole with infinitely many relativistic images and Einstein rings, all of them located beyond a certain critical angle from optic axis and the inner relativistic images all clumped together. However, in the absence of the photon sphere, which is the case for a wide range of parameter values in this spacetime, we show that we get finitely many relativistic images and Einstein rings spaced reasonably apart from one another, some of which can be formed inside the critical angle for the corresponding Schwarzschild black hole. This study suggests that the observation of relativistic images and rings might, in principle, allow us to unravel the existence of the naked singularity in the absence of the photon sphere. Also, the results obtained here are in contrast with the earlier investigation on Janis-Newman-Winicour (JNW) naked singularities where it was shown that the radial caustic is always present in the absence the photon sphere, which is not the case with JMN geometry where radial caustic is absent. We also point out the practical difficulties that might be encountered in the observation of the relativistic images and suggest that new dedicated experiments and techniques have to be developed in future for this purpose.

The leading hadronic contribution to the muon anomalous magnetic moment is given by a weighted integral over euclidean momentum of the hadronic vacuum polarization. This integral is dominated by momenta of order the muon mass. Since the finite volume in lattice QCD makes it difficult to compute the vacuum polarization at a large number of low momenta with high statistics (combined with the fact that one cannot compute it at zero momentum), a parametrization of the vacuum polarization is required to extrapolate the data. A much used functional form is based on vector meson dominance, which introduces model dependence into the lattice computation of the magnetic moment. Here we introduce a model-independent extrapolation method, and present a few first tests of this new method.

Motivated by the recent measurements of nonleptonic ${\overline{B}}_s^0$ decays by the CDF and LHCb collaborations, especially the large $\mathcal{B}({\overline{B}}_s^0\to {\pi }^{+}{\pi }^{-})$, we revisit the hard spectator and annihilation corrections in ${\overline{B}}_s^0$ decays within a QCD factorization approach, with two schemes for the possible parameters for the known end-point divergence appearing in the estimation of the hard spectator and annihilation diagrams. The first one is to conservatively estimate the possible contributions by parametrization (scheme I); another one uses an infrared finite gluon propagator (scheme II) to regulate the end-point singularity. In scheme I, with the constraints from the measured ${\overline{B}}_s^0\to PP(VV)$ decays, two (four) restricted solutions of the parameter spaces are found. In scheme II, we find that most of the theoretical predictions agree well with the experimental data with a single parameter $m_g\sim 0.5\mathrm{GeV}$. However, within both schemes, $\mathcal{B}({\overline{B}}_s^0\to \varphi \varphi )$ are always much larger than $\mathcal{B}({\overline{B}}_s^0\to K^{*0}{\overline{K}}^{*0})$, in contrast to the experimental results $\mathcal{B}({\overline{B}}_s^0\to \varphi \varphi )\simeq \mathcal{B}({\overline{B}}_s^0\to K^{*0}{\overline{K}}^{*0})$. It is noted that the pattern $\mathcal{B}({\overline{B}}_s^0\to \varphi \varphi )>\mathcal{B}({\overline{B}}_s^0\to K^{*0}{\overline{K}}^{*0})$ also persists in other theoretical frameworks; thus, the present experimental result $\mathcal{B}({\overline{B}}_s^0\to \varphi \varphi )\simeq \mathcal{B}({\overline{B}}_s^0\to K^{*0}{\overline{K}}^{*0})$ raises a challenge to theoretical approaches for B nonleptonic decays. Further refined measurements and theoretical studies are called for to resolve such a possible anomaly.

With the advent of the recent measurements in neutrino physics, we investigate the role of high-energy neutrino flux ratios at neutrino telescopes for the possibility of determining the leptonic $CP$-violating phase $\delta$ and the underlying pattern of the leptonic mixing matrix. We find that the flux ratios show a dependence of $\mathcal{O}(10\%)$ on the $CP$-violating phase, and for optimistic uncertainties on the flux ratios less than 10%, they can be used to distinguish between $CP$-conserving and $CP$-violating values of the phase at $2\sigma$ in a nonvanishing interval around the maximal value $|\delta |=\pi /2$.

We construct fermionic Lagrangians with anisotropic scaling $z=2$, the natural counterpart of the usual $z=2$ Lifshitz field theories for scalar fields. We analyze the issue of chiral symmetry, construct the Noether axial currents and discuss the chiral anomaly giving explicit results for two-dimensional case. We also exploit the connection between detailed balance and the dynamics of Lifshitz theories to find different $z=2$ fermionic Lagrangians and construct their supersymmetric extensions.

The Casimir-Polder interaction potential is evaluated for a polarizable microparticle and a conducting wall in the geometry of a cosmic string perpendicular to the wall. The general case of the anisotropic polarizability tensor for the microparticle is considered. The corresponding force is a function of the wall-microparticle and cosmic string-microparticle distances. Depending on the orientation of the polarizability tensor principal axes the force can be either attractive or repulsive. The asymptotic behavior of the Casimir-Polder potential is investigated at large and small separations compared to the wavelength of the dominant atomic transitions. We show that the conical defect may be used to control the strength and the sign of the Casimir-Polder force.

We show that the two-point function $\sigma (x,x^{\prime })=\sqrt{⟨[\varphi (x)-\varphi (x^{\prime }){]}^2⟩}$ of a scalar quantum field theory is a metric (i.e., a symmetric positive function satisfying the triangle inequality) on space-time (with imaginary time). It is very different from the Euclidean metric $|x-x^{\prime }|$ at large distances, yet agrees with it at short distances. For example, space-time has a finite diameter that is not universal. The Lipschitz equivalence class of the metric is independent of the cutoff. $\sigma (x,x^{\prime })$ is not the length of the geodesic in any Riemannian metric. Nevertheless, it is possible to embed space-time in a higher dimensional space so that $\sigma (x,x^{\prime })$ is the length of the geodesic in the ambient space. $\sigma (x,x^{\prime })$ should be useful in constructing the continuum limit of quantum field theory with fundamental scalar particles.

Various regularization methods have been used to compute the self-force acting on a static particle in a static, curved spacetime. Many of these are based on Hadamard’s two-point function in three dimensions. On the other hand, the regularization method that enjoys the best justification is that of Detweiler and Whiting, which is based on a four-dimensional Green’s function. We establish the connection between these methods and find that they are all equivalent, in the sense that they all lead to the same static self-force. For general static spacetimes, we compute local expansions of the Green’s functions on which the various regularization methods are based. We find that these agree up to a certain high order, and conjecture that they might be equal to all orders. We show that this equivalence is exact in the case of ultrastatic spacetimes. Finally, our computations are exploited to provide regularization parameters for a static particle in a general static and spherically symmetric spacetime.

The inspiral and merger of a binary neutron star (NSNS) can lead to the formation of a hypermassive neutron star (HMNS). As the HMNS loses thermal pressure due to neutrino cooling and/or centrifugal support due to gravitational wave emission, and/or magnetic breaking of differential rotation, it will collapse to a black hole. To assess the importance of shock-induced thermal pressure and cooling, we adopt an idealized equation of state and perform NSNS simulations in full general relativity through late inspiral, merger, and HMNS formation, accounting for cooling. We show that thermal pressure contributes significantly to the support of the HMNS against collapse and that thermal cooling accelerates its “delayed” collapse. Our simulations demonstrate explicitly that cooling can induce the catastrophic collapse of a hot hypermassive neutron star formed following the merger of binary neutron stars. Thus, cooling physics is important to include in NSNS merger calculations to accurately determine the lifetime of the HMNS remnant and to extract information about the neutron star equation of state, cooling mechanisms, bar instabilities and B-fields from the gravitational waves emitted during the transient phase prior to black hole formation.

We examine an Unruh-DeWitt particle detector coupled to a scalar field in three-dimensional curved spacetime. We first obtain a regulator-free expression for the transition probability in an arbitrary Hadamard state, working within first-order perturbation theory and assuming smooth switching, and we show that both the transition probability and the instantaneous transition rate remain well defined in the sharp switching limit. We then analyze a detector coupled to a massless conformally coupled field in the Hartle-Hawking vacua on the Bañados-Teitelboim-Zanelli black hole, under both transparent and reflective boundary conditions at the infinity. A selection of stationary and freely falling detector trajectories are examined, including the corotating trajectories, for which the response is shown to be thermal. Analytic results in a number of asymptotic regimes, including those of large and small mass, are complemented by numerical results in the interpolating regimes. The boundary condition at infinity is seen to have a significant effect on the transition rate.

We present the first numerical approximation of the scalar Schwarzschild Green function in the time domain, which reveals several universal features of wave propagation in black hole spacetimes. We demonstrate the trapping of energy near the photon sphere and confirm its exponential decay. The trapped wavefront passes through caustics resulting in echoes that propagate to infinity. The arrival times and the decay rate of these caustic echoes are consistent with propagation along null geodesics and the large $\ell$ limit of quasinormal modes. We show that the fourfold singularity structure of the retarded Green function is due to the well-known action of a Hilbert transform on the trapped wavefront at caustics. A twofold cycle is obtained for degenerate source-observer configurations along the caustic line, where the energy amplification increases with an inverse power of the scale of the source. Finally, we discuss the tail piece of the solution due to propagation within the light cone, up to and including null infinity, and argue that, even with ideal instruments, only a finite number of echoes can be observed. Putting these pieces together, we provide a heuristic expression that approximates the Green function with a few free parameters. Accurate calculations and approximations of the Green function are the most general way of solving for wave propagation in curved spacetimes and should be useful in a variety of studies such as the computation of the self-force on a particle.

We explore the generic motion of cosmic (super)strings with warped internal dimensions. We find no dynamical mechanism that localizes the string at the tip of the throat, but rather that the motion has both internal and external degrees of freedom. We present some numerical simulations using the Klebanov-Strassler solution as an explicit sample throat geometry. The results indicate that cosmic (super)strings formed by inflationary brane-antibrane annihilation can have sufficient internal motion for the gravitational wave signals from the string network to be suppressed relative to the signal from a “standard” cosmic string network.