The generalized second law (GSL) of black hole thermodynamics states that the sum of changes in black hole entropy and the ordinary entropy of matter and fields outside the hole must be non-negative. In the classical limit, the GSL reduces to Hawking’s area theorem. Neither law identifies the specific effects that make it work in particular situations. Motivated by Davies’ recent gedanken experiment he used to infer a bound on the size of the fine structure constant from the GSL, we study a series of variants in which an electric test charge is lowered to a finite radius and then dropped into a Schwarzschild, a near-extremal magnetic Reissner-Nordström or a near-extremal Kerr black hole. For a classical charge, we demonstrate that a specific “backreaction” effect is responsible for protecting the area theorem in the near-extremal examples. For the magnetically charged Reissner-Nordström hole an area theorem violation is defused by taking into account a subtle source of repulsion of the charge: the spinning up of the black hole in the process of bringing the charge down to its dropping point. In Kerr hole case, the electric self-force on the charge is sufficient to right matters. However, in all experiments involving an elementary charge, the full GSL would apparently be violated were the fine structure constant greater than about order unity. We argue that in this case a quantum effect, the Unruh-Wald quantum buoyancy, may protect the GSL.

In [arXiv:0803.3259] the equations describing the parallel transport of orthonormal frames along timelike (spacelike) geodesics in a spacetime admitting a nondegenerate principal conformal Killing-Yano 2-form $\mathit{h}$ were solved. The construction employed is based on studying the Darboux subspaces of the 2-form $\mathit{F}$ obtained as a projection of $\mathit{h}$ along the geodesic trajectory. In this paper we demonstrate that, although slightly modified, a similar construction is possible also in the case of null geodesics. In particular, we explicitly construct the parallel-transported frames along null geodesics in $D=4$, 5, 6 Kerr-NUT-(A)dS spacetimes. We further discuss the parallel transport along principal null directions in these spacetimes. Such directions coincide with the eigenvectors of the principal conformal Killing-Yano tensor. Finally, we show how to obtain a parallel-transported frame along null geodesics in the background of the 4D Plebański-Demiański metric which admits only a conformal generalization of the Killing-Yano tensor.

Uniqueness problems in the elliptic sector of constrained formulations of Einstein equations have a dramatic effect on the physical validity of some numerical solutions, for instance, when calculating the spacetime of very compact stars or nascent black holes. The fully constrained formulation (FCF) proposed by Bonazzola, Gourgoulhon, Grandclément, and Novak is one of these formulations. It contains, as a particular case, the approximation of the conformal flatness condition (CFC) which, in the last ten years, has been used in many astrophysical applications. The elliptic part of the FCF basically shares the same differential operators as the elliptic equations in the CFC scheme. We present here a reformulation of the elliptic sector of the CFC that has the fundamental property of overcoming the local uniqueness problems. The correct behavior of our new formulation is confirmed by means of a battery of numerical simulations. Finally, we extend these ideas to the FCF, complementing the mathematical analysis carried out in previous studies.

We analyze the Hawking radiation process due to collapsing configurations in the presence of superluminal modifications of the dispersion relation. With such superluminal dispersion relations, the horizon effectively becomes a frequency-dependent concept. In particular, at every moment of the collapse, there is a critical frequency above which no horizon is experienced. We show that, as a consequence, the late-time radiation suffers strong modifications, both quantitative and qualitative, compared to the standard Hawking picture. Concretely, we show that the radiation spectrum becomes dependent on the measuring time, on the surface gravities associated with different frequencies, and on the critical frequency. Even if the critical frequency is well above the Planck scale, important modifications still show up.

I aim to quantify the distribution of information in the Hawking radiation and inside the black hole in the semiclassical evaporation process. The structure of relativistic quantum field theory does not allow one to define a localized entropy unambiguously, but rather forces one to consider the shared information (mutual information) between two different regions of space-time. Using this tool, I first show that the entropy of a thermal gas at the Unruh temperature underestimates the actual amount of (shared) information present in a region of the Rindler space. Then, I analyze the mutual information between the black hole and the late time radiation region. A well-known property of the entropy implies that this is monotonically increasing with time. This means that in the semiclassical picture it is not possible to recover the eventual purity of the initial state in the final Hawking radiation through subtle correlations established during the whole evaporation period, no matter the interactions present in the theory. I find extensivity of the entropy as a consequence of a reduction to a two dimensional conformal problem in a simple approximation. However, the extensivity of information in the radiation region in a full four dimensional calculation seems not to be guaranteed on general grounds. I also analyze the localization of shared information inside the black hole finding that a large amount of it is contained in a small, approximately flat region of space-time near the point where the horizon begins. This gives place to large violations of the entropy bounds. I show that this problem is not eased by backscattering effects and argue that a breaking of conformal invariance is necessary to delocalize the entropy. Finally, I indicate that the mutual information could lead to a way to understand the Bekenstein-Hawking black hole entropy which does not require a drastic reduction in degrees of freedom in order to regulate the entanglement entropy. On the contrary, a large number of field degrees of freedom at high energies giving place to a Hagedorn transition implements a natural distance cutoff in the mutual information, which may in consequence turn out to be bounded.

We study the instability of small AdS black holes with two independent rotation parameters in minimal five-dimensional gauged supergravity to massless scalar perturbations. We analytically solve the Klein-Gordon equation for low-frequency perturbations in two regions of the spacetime of these black holes: namely, in the region close to the horizon and in the far-region. By matching the solutions in an intermediate region, we calculate the frequency spectrum of quasinormal modes. We show that in the regime of superradiance only the modes of even orbital quantum number undergo negative damping, resulting in exponential growth of the amplitude. That is, the black holes become unstable to these modes. Meanwhile, the modes of odd orbital quantum number do not undergo any damping, oscillating with frequency-shifts. This is in contrast with the case of four-dimensional small Kerr-AdS black holes which exhibit the instability to all modes of scalar perturbations in the regime of superradiance.

Annihilation of dark matter usually produces together with gamma rays comparable amounts of electrons and positrons. The $e^{+}{e}^{-}$ gyrating in the galactic magnetic field then produce secondary synchrotron radiation which thus provides an indirect means to constrain the DM signal itself. To this purpose, we calculate the radio emission from the galactic halo as well as from its expected substructures and we then compare it with the measured diffuse radio background. We employ a multifrequency approach using data in the relevant frequency range 100 MHz–100 GHz, as well as the WMAP haze data at 23 GHz. The derived constraints are of the order $⟨{\sigma }_{\mathrm{A}}v⟩={10}^{-24}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ for a DM mass $m_{\chi }=100\mathrm{GeV}$ sensibly depending, however, on the astrophysical uncertainties, in particular, on the assumption of the galactic magnetic field model. The signal from single bright clumps is instead largely attenuated by diffusion effects and offers only poor detection perspectives.

We present a coherent theoretical framework for computing gravitational lensing effects and redshift-space distortions in an inhomogeneous universe and investigate their impacts on galaxy two-point statistics. Adopting the linearized Friedmann-Lemaître-Robertson-Walker metric, we derive the gravitational lensing and the generalized Sachs-Wolfe effects that include the weak lensing distortion, magnification, and time delay effects, and the redshift-space distortion, Sachs-Wolfe, and integrated Sachs-Wolfe effects, respectively. Based on this framework, we first compute their effects on observed source fluctuations, separating them as two physically distinct origins: the volume effect that involves the change of volume and is always present in galaxy two-point statistics, and the source effect that depends on the intrinsic properties of source populations. Then we identify several terms that are ignored in the standard method, and we compute the observed galaxy two-point statistics, an ensemble average of all the combinations of the intrinsic source fluctuations and the additional contributions from the gravitational lensing and the generalized Sachs-Wolfe effects. This unified treatment of galaxy two-point statistics clarifies the relation of the gravitational lensing and the generalized Sachs-Wolfe effects to the metric perturbations and the underlying matter fluctuations. For near-future dark energy surveys, we compute additional contributions to the observed galaxy two-point statistics and analyze their impact on the anisotropic structure. Thorough theoretical modeling of galaxy two-point statistics would be not only necessary to analyze precision measurements from upcoming dark energy surveys, but also provide further discriminatory power in understanding the underlying physical mechanisms.

The abundance and distribution of collapsed objects such as galaxy clusters will become an important tool to investigate the nature of dark energy and dark matter. Number counts of very massive objects are sensitive not only to the equation of state of dark energy, which parametrizes the smooth component of its pressure, but also to the sound speed of dark energy, which determines the amount of pressure in inhomogeneous and collapsed structures. Since the evolution of these structures must be followed well into the nonlinear regime, and a fully relativistic framework for this regime does not exist yet, we compare two approximate schemes: the widely used spherical collapse model and the pseudo-Newtonian approach. We show that both approximation schemes convey identical equations for the density contrast, when the pressure perturbation of dark energy is parametrized in terms of an effective sound speed. We also make a comparison of these approximate approaches to general relativity in the linearized regime, which lends some support to the approximations.

Light dark matter annihilating into electron-positron pairs emits a significant amount of internal bremsstrahlung that may contribute to the cosmic gamma-ray background. The amount of emitted gamma-rays depends on the dark matter clumping factor. Recent calculations indicate that this value should be of order ${10}^6-{10}^7$. That allows us to calculate the expected gamma-ray background contribution from dark matter annihilation. We find that the light dark matter model can be ruled out if a constant thermally-averaged cross section is assumed (s-wave annihilation). For more massive dark matter candidates like neutralinos, however, cosmic constraints are weaker.

We study a particular nonlinear dispersion relation ${\omega }_p(k_p)$—a series expansion in the physical wave number $k_p$—for modeling first-order corrections in the equation of motion of a test scalar field in a de Sitter spacetime from trans-Planckian physics in cosmology. Using both a numerical approach and a semianalytical one, we show that the WKB approximation previously adopted in the literature should be used with caution, since it holds only when the comoving wave number $k\gg aH$. We determine the amplitude and behavior of the corrections on the power spectrum for this test field. Furthermore, we consider also a more realistic model of inflation, the power-law model, using only a numerical approach to determine the corrections on the power spectrum.

Since Witten’s seminal 1984 paper on the subject, searches for evidence of strange quark nuggets (SQNs) have proven unsuccessful. In the absence of experimental evidence ruling out SQNs, the validity of theories introducing mechanisms that increase their stability should continue to be tested. To stimulate electromagnetic SQN searches, particularly space searches, we estimate the net charge that would develop on a SQN in space exposed to various radiation baths (and showers) capable of liberating the SQN’s less strongly bound electrons, taking into account recombination with ambient electrons. We consider, in particular, the cosmic microwave background, radiation from the sun, and diffuse galactic and extragalactic ultraviolet backgrounds. The largest charge, for the settings considered, develops on a solar system SQN exposed to a solar X-ray flare. A possible dramatic signal of SQNs in explosive astrophysical events is noted.

Recently, the DAMA/LIBRA Collaboration has repeated and reinforced their claim to have detected an annual modulation in their signal rate, and have interpreted this observation as evidence for dark-matter particles at the $8.2\sigma$ confidence level. Furthermore, it has also been noted that the effects of channeling may enable a weakly interacting massive particle (WIMP) that scatters elastically via spin-independent interactions from nuclei to produce the signal observed by DAMA/LIBRA without exceeding the limits placed by CDMS, XENON, CRESST, CoGeNT, and other direct-detection experiments. To accommodate this elastic-scattering explanation, however, the mass of the responsible dark-matter particle must be relatively light, $m_{\mathrm{DM}}\lesssim 10\mathrm{GeV}$. Such dark-matter particles will become captured by and annihilate in the Sun at very high rates, leading to a potentially large flux of GeV-scale neutrinos. We calculate the neutrino spectrum resulting from WIMP annihilations in the Sun and show that existing limits from Super-Kamiokande can be used to close a significant portion of the DAMA region, especially if the dark-matter particles produce tau leptons or neutrinos in a sizable fraction of their annihilations. We also determine the spin-dependent WIMP-nuclei elastic-scattering parameter space consistent with DAMA. The constraints from Super-Kamiokande on the spin-dependent scenario are even more severe—they exclude any self-annihilating WIMP in the DAMA region that annihilates 1% of the time or more to any combination of neutrinos, tau leptons, or charm or bottom quarks.

In the context of warped scenarios in which standard model (SM) fields are allowed to propagate in the bulk, we revisit the possible mixing between the IR localized Higgs field and the radion graviscalar. The phenomenology of the resulting mostly Higgs field does not suffer important deviations with respect to the case in which all the SM is localized in the IR brane (original Higgs-radion mixing scenario). On the contrary, the phenomenology of the mostly radion field can present important differences with respect to the original scenario. At the LHC, the most striking effect is now the possibility of sizable radion decays into photons in a mass range well beyond the $ZZ$ and $WW$ thresholds, not due to dramatically enhanced couplings to photons but to suppressed couplings to massive fields.

We examine the predictions for both the spin-dependent and spin-independent direct detection rates in a variety of new particle physics models with dark matter candidates. We show that a determination of both spin-independent and spin-dependent amplitudes on protons and neutrons can in principle discriminate different candidates of dark matter up to a few ambiguities. We emphasize the importance of making measurements with different spin-dependent sensitive detector materials and the need for significant improvement of the detector sensitivities. Scenarios where exchange of new colored particles contributes significantly to the elastic scattering cross sections are often the most difficult to identify, the LHC should give an indication whether such scenarios are relevant for direct detection.

We present the first lattice QCD calculation of the form factor for $\overline{B}\to D^{*}\ell \overline{\nu }$ with three flavors of sea quarks. We use an improved staggered action for the light valence and sea quarks (the MILC configurations), and the Fermilab action for the heavy quarks. The form factor is computed at zero recoil using a new double ratio method that yields the form factor more directly than the previous Fermilab method. Other improvements over the previous calculation include the use of much lighter light-quark masses, and the use of lattice (staggered) chiral perturbation theory in order to control the light-quark discretization errors and chiral extrapolation. We obtain for the form factor, ${\mathcal{F}}_{B\to D^{*}}(1)=0.921(13)(20)$, where the first error is statistical and the second is the sum of all systematic errors in quadrature. Applying a 0.7% electromagnetic correction and taking the latest PDG average for ${\mathcal{F}}_{B\to D^{*}}(1)|V_{cb}|$ leads to $|V_{cb}|=(38.7\pm {0.9}_{\exp }\pm {1.0}_{\mathrm{theo}})\times {10}^{-3}$.

Fixing a gauge in the nonperturbative domain of Yang-Mills theory is a nontrivial problem due to the presence of Gribov copies. In particular, there are different gauges in the nonperturbative regime which all correspond to the same definition of a gauge in the perturbative domain. Gauge-dependent correlation functions may differ in these gauges. Two such gauges are the minimal Landau gauge and the absolute Landau gauge, both corresponding to the perturbative Landau gauge. These, and their numerical implementation, are described and presented in detail. Other choices will also be discussed. This investigation is performed, using numerical lattice gauge theory calculations, by comparing the propagators of gluons and ghosts for the minimal Landau gauge and the absolute Landau gauge in SU(2) Yang-Mills theory. It is found that the propagators are different in the far infrared and even at energy scales of the order of half a GeV. In particular, the finite-volume effects are also modified. This is observed in two and three dimensions. Some remarks on the four-dimensional case are provided as well.

The dominance of ${\chi }_0$ in the data for $e^{+}{e}^{-}\to \psi +{\chi }_J(c\overline{c})$ is shown to violate Okubo-Zweig-Iizuka rule factorization. Single gluon exchange gives a nonfactorizing effective $\mathbf{S}·\mathbf{L}$ interaction that generates a large scalar production amplitude. This also has observable effects near threshold in $e^{+}{e}^{-}\to D^{(*)}{D}_J$, where enhancements of $D^{*}{D}_0$ and $D{D}_1$ channels are predicted. Further tests and implications are discussed.

We describe a method for measuring $CP$-violation parameters from which the Cabibbo-Kobayashi-Maskawa angle $\gamma$ may be extracted. The method makes use of the total decay rates in $B^{\pm }\to D{K}^{\pm }$ decays, where the neutral $D$ meson decays to multibody final states. We analyze the error of the method using experimental $CP$-violation analysis variables that enable straightforward sensitivity comparison with other methods for extracting $\gamma$, and discuss the use of $B$-factory and charm-factory data to obtain the relevant charm-decay information needed for this measurement. Measurement sensitivities are estimated for the currently available $B$-factory data sample, and $D$ decay modes for which use of this method can make a significant contribution toward reducing the total error on $\gamma$ are identified.