Black holes are important astrophysical objects describing an end state of stellar evolution, which are observed frequently. There are theoretical predictions that Kerr black holes with high spins expel magnetic fields. However, Kerr black holes are pure vacuum solutions, which do not include accretion disks, and additionally previous investigations are mainly limited to weak magnetic fields. We prove for the first time in full general relativity that generic rapidly spinning black holes including those deformed by accretion disks still expel even strong magnetic fields. Analogously to a similar property of superconductors, this is called the Meissner effect.

We propose a novel branch of the Galilean genesis scenario as an alternative to inflation, in which the Universe starts expanding from Minkowski in the asymptotic past with a gross violation of the null energy condition (NEC). This variant, described by several functions and parameters within the Horndeski scalar-tensor theory, shares the same background dynamics with the existing genesis models, but the nature of primordial quantum fluctuations is quite distinct. In some cases, tensor perturbations grow on superhorizon scales. The tensor power spectrum can be red, blue, or scale invariant, depending on the model, while scalar perturbations are nearly scale invariant. This is in sharp contrast to typical NEC-violating cosmologies, in which a blue tensor tilt is generated. Though the primordial tensor and scalar spectra are both nearly scale invariant as in the inflationary scenario, the consistency relation in our variant of Galilean genesis is nonstandard.

Some classes of inflationary models naturally introduce two distinct metrics/frames, and their equivalence in terms of observables has often been put in question. D-brane inflation proposes candidates for an inflaton embedded in the string theory and possesses descriptions on the brane and bulk metrics/frames, which are connected by a conformal/disformal transformation that depends on the inflaton and its derivatives. It has been shown that curvature perturbations generated by the inflaton are identical in both frames, meaning that observables such as the spectrum of cosmic microwave background (CMB) anisotropies are independent of whether matter fields—including those in the standard model of particle physics—minimally couple to the brane or the bulk metric/frame. This is true despite the fact that the observables are eventually measured by the matter fields and that the total action including the matter fields is different in the two cases. In contrast, in curvaton scenarios, the observables depend on the frame to which the curvaton minimally couples. Among all inflationary scenarios, we focus on two models motivated by the KKLMMT fine-tuning problem: a slow-roll inflation with an inflection-point potential and a model of a rapidly rolling inflaton that conformally couples to gravity. In the first model, the difference between the frames in which the curvaton resides is encoded in the spectral index of the curvature perturbations, depicting the nature of the frame transformation. In the second model, the curvaton on the brane induces a spectral index significantly different from that in the bulk and is even falsified by the observations. This work thus demonstrates that two frames connected by a conformal/disformal transformation lead to different physical observables such as CMB anisotropies in curvaton models.

We propose an efficient way to test rotational invariance in the cosmological perturbations by use of galaxy correlation functions. In symmetry-breaking cases, the galaxy power spectrum can have extra angular dependence in addition to the usual one due to the redshift-space distortion, $\widehat{k}·\widehat{n}$. We confirm that, via the decomposition into not the usual Legendre basis ${\mathcal{L}}_{\ell }(\widehat{k}·\widehat{n})$ but the bipolar spherical harmonic one $\{Y_{\ell }(\widehat{k})\otimes Y_{{\ell }^{\prime }}(\widehat{n}){\}}_{LM}$, the symmetry-breaking signal can be completely distinguished from the usual isotropic one since the former yields nonvanishing $L\ge 1$ modes but the latter is confined to the $L=0$ one. As a demonstration, we analyze the signatures due to primordial-origin symmetry breakings such as the well-known quadrupolar-type and dipolar-type power asymmetries and find nonzero $L=2$ and 1 modes, respectively. Fisher matrix forecasts of their constraints indicate that the Planck-level sensitivity could be achieved by the SDSS or BOSS-CMASS data, and an order-of-magnitude improvement is expected in a near future survey as PFS or Euclid by virtue of an increase in accessible Fourier mode. Our methodology is model-independent and hence applicable to the searches for various types of statistically anisotropic fluctuations.

The spectral shape of cosmic ray positrons and antiprotons has been accurately measured in the broad kinetic energy range 1–350 GeV. In the higher part of this range ($E\gtrsim 30\mathrm{GeV}$), the $e^{+}$ and $\overline{p}$ are both well described by power laws with spectral indices ${\gamma }_{e^{+}}\simeq 2.77\pm 0.02$ and ${\gamma }_{\overline{p}}\simeq 2.78\pm 0.04$ that are approximately equal to each other and to the spectral index of protons. In the same energy range, the positron-antiproton flux ratio has the approximately constant value $2.04\pm 0.04$, that is consistent with being equal to the ratio $e^{+}/\overline{p}$ calculated for the conventional mechanism of production, where the antiparticles are created as secondaries in the inelastic interactions of primary cosmic rays with interstellar gas. The positron-antiproton ratio at lower energy is significantly higher (reaching a value $e^{+}/\overline{p}\approx 100$ for $E\approx 1\mathrm{GeV}$), but, in the entire energy range 1–350 GeV, the flux ratio is consistent with being equal to the ratio of the production rates in the conventional mechanism, as the production of low-energy antiprotons is kinematically suppressed in collisions with a target at rest. These results strongly suggest that cosmic ray positrons and antiprotons have a common origin as secondaries in hadronic interactions. This conclusion has broad implications for the astrophysics of cosmic rays in the Galaxy.

An energy-extracting black hole magnetosphere can be defined by the location of its inner Alfvén surface, which determines the rate of black hole energy extraction along a given magnetic field line. We study how the location of the inner Alfvén surface can modify the structure of energy-extracting black hole magnetospheres in the force-free limit. Hundreds of magnetospheres are numerically computed via a general-relativistic extension of the Newtonian magnetofrictional method for a full range of black hole spins and flow parameters. We find that jet-like structures naturally form very close to the horizon for Alfvén surfaces near the boundary of the ergosphere and that energy is extracted towards the equatorial plane for Alfvén surfaces close to the horizon. This suggests that two broad classes of energy-extracting black hole magnetospheres might exist: those that transmit extracted energy directly to distant observers, and those that transmit extracted energy to nearby accreting matter. Applied to transient high-energy phenomena, we find that they might also differ in time scale by a factor of 20 or more.

We explore a new low-threshold direct-detection concept for dark matter, based on the breaking of chemical bonds between atoms. This includes the dissociation of molecules and the creation of defects in a lattice. With thresholds of a few to 10s of eV, such an experiment could probe the nuclear couplings of dark matter particles as light as a few MeV. We calculate the expected rates for dark matter to break apart diatomic molecules, which we take as a case study for more general systems. We briefly mention ideas for how chemical-bond breaking might be detected in practice. We also discuss the possibility of detecting solar neutrinos, including pp neutrinos, with this experimental concept. With an event rate of $\mathcal{O}(0.1/\mathrm{kg}\text{−}\mathrm{year})$, large exposures are required, but measuring low-energy solar neutrinos would provide a crucial test of the solar model.

The Polyakov–Nambu–Jona-Lasinio model has been quite successful in describing various qualitative features of observables for strongly interacting matter, that are measurable in heavy-ion collision experiments. The question still remains on the quantitative uncertainties in the model results. Such an estimation is possible only by contrasting these results with those obtained from first principles using the lattice QCD framework. Recently a variety of lattice QCD data were reported in the realistic continuum limit. Here we make a first attempt at reparametrizing the model so as to reproduce these lattice data. We find excellent quantitative agreement for the equation of state. Certain discrepancies in the charge and strangeness susceptibilities as well as baryon-charge correlation still remain. We discuss their causes and outline possible directions to remove them.

I propose a general, covariant way of defining when one region is “deeper in the bulk” than another. This definition is formulated outside of an event horizon (or in the absence thereof) in generic geometries; it may be applied to both points and surfaces, and it may be used to compare the depth of bulk points or surfaces relative to a particular boundary subregion or relative to the entire boundary. Using the recently proposed “light-cone cut” formalism, the comparative depth between two bulk points can be determined from the singularity structure of Lorentzian correlators in the dual field theory. I prove that, by this definition, causal wedges of progressively larger regions probe monotonically deeper in the bulk. The definition furthermore matches expectations in pure AdS and in static AdS black holes with isotropic spatial slices, where a well-defined holographic coordinate exists. In terms of holographic renormalization group flow, this new definition of bulk depth makes contact with coarse graining over both large distances and long time scales.

We study the Casimir interaction between a perfectly conducting sphere and plate in the classical limit of high temperatures. By taking the small-distance expansion of the exact scattering formula, we compute the leading correction to the Casimir energy beyond the commonly employed proximity force approximation. We find that for a sphere of radius $R$ at a distance $d$ from the plate the correction is of the form ${\ln }^2(d/R)$, in agreement with indications from recent large-scale numerical computations. We develop a fast-converging numerical scheme for computing the Casimir interaction to high precision, based on bispherical partial waves, and we verify that the short-distance formula provides precise values of the Casimir energy also for fairly large distances.

The decays of excited bosonic and excited fermionic modes in the external field of the domain wall are studied. The wave functions of the excited fermionic modes are found analytically in the external field approximation. Some properties of the fermionic modes are investigated. The reflection and transmission coefficients are calculated for fermion scattering from the domain wall. Properties of the reflection and transmission coefficients are studied. The decays of the first excited fermionic mode are investigated to the first order in the Yukawa coupling constant. The amplitudes, angular distributions, and widths of these decays are found by analytical and numerical methods. Decays of the excited bosonic mode are also investigated to the first order in the Yukawa and self-interaction coupling constants. The amplitudes, angular distributions, and widths of these decays are obtained analytically and by numerical methods.

Ongoing astronomical efforts extract physical properties of black holes from electromagnetic emissions in their near-vicinity. This requires finding the null geodesics which extend from the near-horizon region out to a distant observatory. In general these are given by elliptic integrals which are often studied numerically. In this paper, for the interesting special case of extremally spinning Kerr black holes, we use an emergent near-horizon conformal symmetry to find near-superradiant geodesics analytically in terms of elementary functions.

We study the development of caustics in shift-symmetric scalar field theories by focusing on simple waves with an $SO(p)$-symmetry in an arbitrary number of space dimensions. We show that the pure Galileon, the DBI–Galileon, and the extreme-relativistic Galileon naturally emerge as the unique set of caustic-free theories, highlighting a link between the caustic-free condition for simple $SO(p)$-waves and the existence of either a global Galilean symmetry or a global (extreme-)relativistic Galilean symmetry.

We consider big bang nucleosynthesis and the cosmic microwave background when both the neutrino temperature and neutrino number are allowed to vary from their standard values. The neutrino temperature is assumed to differ from its standard model value by a fixed factor from big bang nucleosynthesis up to the present. In this scenario, the effective number of relativistic degrees of freedom, $N_{\mathrm{eff}}^{\mathrm{CMB}}$, derived from observations of the cosmic microwave background is not equal to the true number of neutrinos, $N_{\nu }$. We determine the element abundances predicted by big bang nucleosynthesis as a function of the neutrino number and temperature, converting the latter to the equivalent value of $N_{\mathrm{eff}}^{\mathrm{CMB}}$. We find that a value of $N_{\mathrm{eff}}^{\mathrm{CMB}}\approx 3$ can be made consistent with $N_{\nu }=4$ with a decrease in the neutrino temperature of $\sim 5\%$, while $N_{\nu }=5$ is excluded for any value of $N_{\mathrm{eff}}^{\mathrm{CMB}}$. No observationally allowed values for $N_{\mathrm{eff}}^{\mathrm{CMB}}$ and $N_{\nu }$ can solve the lithium problem.

A primordial magnetic field (PMF) present before recombination can leave specific signatures on the cosmic microwave background (CMB) fluctuations. Of particular importance is its contribution to the B-mode polarization power spectrum. Indeed, vortical modes sourced by the PMF can dominate the B-mode power spectrum on small scales, as they survive damping up to a small fraction of the Silk length. Therefore, measurements of the B-mode polarization at high $\ell$, such as the one recently performed by the South Pole Telescope (SPT), have the potential to provide stringent constraints on the PMF. We use the publicly released SPT B-mode polarization spectrum, along with the temperature and polarization data from the Planck satellite, to derive constraints on the magnitude, the spectral index and the energy scale at which the PMF was generated. We find that, while Planck data constrains the magnetic amplitude to $B_{1\mathrm{Mpc}}<3.3\mathrm{nG}$ at the 95% confidence level (C.L.), the SPT measurement improves the constraint to $B_{1\mathrm{Mpc}}<1.5\mathrm{nG}$. The magnetic spectral index, $n_B$, and the time of the generation of the PMF are unconstrained. For a nearly scale-invariant PMF, predicted by the simplest inflationary magnetogenesis models, the bound from $\mathrm{Planck}+\mathrm{SPT}$ is $B_{1\mathrm{Mpc}}<1.2\mathrm{nG}$ at 95% C.L. For PMF with $n_B=2$, which is expected for fields generated in post-inflationary phase transitions, the 95% C.L. bound is $B_{1\mathrm{Mpc}}<0.002\mathrm{nG}$, corresponding to the magnetic fraction of the radiation density ${\mathrm{\Omega }}_{B\gamma }<{10}^{-3}$ or the effective field $B_{\mathrm{eff}}<100\mathrm{nG}$. The patches for the Boltzmann code camb and the Markov chain Monte Carlo engine CosmoMC, incorporating the PMF effects on CMB, are made publicly available.

Helical intergalactic magnetic fields at the $\sim {10}^{-14}\mathrm{G}$ level on $\sim 10\mathrm{Mpc}$ length scales are indicated by current gamma ray observations. The existence of magnetic fields in cosmic voids and their nontrivial helicity suggest that they must have originated in the early Universe and thus have implications for the fundamental interactions. We derive the spectrum of the cosmological magnetic field as implied by observations and MHD evolution, yielding order nano Gauss fields on kiloparsec scales and a “large helicity puzzle” that needs to be resolved by the fundamental interactions. The importance of $CP$ violation and a possible crucial role for chiral effects or axions in the early Universe are pointed out.

It has been suggested that nonrelativistic outflows from quasars can naturally account for the missing component of the extragalactic $\gamma$-ray background and explain the cumulative neutrino background through pion decay in collisions between protons accelerated by the outflow shock and interstellar protons. Here, we show that the same quasar outflows are capable of accelerating protons to energies of $\sim {10}^{20}\mathrm{eV}$ during the early phase of their propagation. The overall quasar population is expected to produce a cumulative ultrahigh energy cosmic-ray flux of $\sim {10}^{-7}\mathrm{GeV}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}$ at $E_{\mathrm{CR}}\gtrsim {10}^{18}\mathrm{eV}$. The spectral shape and amplitude are consistent with recent observations for outflow parameters constrained to fit secondary $\gamma$ rays and neutrinos without any additional parameter tuning. This indicates that quasar outflows simultaneously account for all three messengers at their observed levels.

Using lunar seismological data, constraints are proposed on the available parameter space of macroscopic dark matter (macros). We show that actual limits are considerably weaker by considering in greater detail the mechanism through which macro impacts generate detectable seismic waves, which have wavelengths considerably longer than the diameter of the macro. We show that the portion of the macro parameter space that can be ruled out by current seismological evidence is considerably smaller than previously reported, and specifically that candidates with greater than or equal to nuclear density are not excluded by lunar seismology.

The self-energy of the $\mathrm{\Delta }$ baryon is evaluated at a finite temperature and density using the real-time formalism of thermal field theory. The Dyson-Schwinger equation is used to get the exact thermal propagator followed by the spectral function of $\mathrm{\Delta }$. The $\pi N$ scattering cross section obtained using an explicit $\mathrm{\Delta }$ exchange is normalized to the experimental data in the vacuum, and its medium modification is implemented by means of the exact thermal propagator. A significant suppression of the peak of the cross section is observed at a higher temperature and baryon density. Effects on the mean relaxation time of nucleons and the temperature dependence of the shear viscosity of a pion nucleon gas are demonstrated.