This work is devoted to the study of photon trajectories around rotating boson stars. The basic properties of boson star models are given with a particular emphasis on the high compactness those objects can have. Using an effective potential method, circular orbits of photons around rotating boson stars are then obtained, at least for relativistic enough configurations. A particular class of light rings, in which the photons are at rest on a stable orbit, is exhibited. By this, one means that the associated worldline is collinear to the Killing vector corresponding to the asymptotic time translation symmetry. It is proposed to call those orbits light points. Their existence is very specific to boson stars, and the link between light points and ergoregions is investigated.

When bosonic matter in the form of a complex scalar field is added to Ellis wormholes, the phenomenon of spontaneous symmetry breaking is observed. Symmetric solutions possess full reflection symmetry with respect to the radial coordinate of the two asymptotically flat spacetime regions connected by the wormhole, whereas asymmetric solutions do not possess this symmetry. Depending on the size of the throat, at bifurcation points pairs of asymmetric solutions arise from or merge with the symmetric solutions. These asymmetric solutions are energetically favored. When the backreaction of the boson field is taken into account, this phenomenon is retained. Moreover, in a certain region of the solution space both symmetric and asymmetric solutions exhibit a transition from single throat to double throat configurations.

Bouncing solutions are obtained from a generally covariant action characterized by a potential which is a nonlocal functional of the dilaton field at two separated space-time points. Gradient instabilities are shown to arise in this context but they are argued to be nongeneric. After performing a gauge-invariant and a frame-invariant derivation of the evolution equations of the fluctuations, a heuristic criterion for the avoidance of pathological instabilities is proposed and corroborated by a number of explicit examples that turn out to be compatible with a quasiflat spectrum of curvature inhomogeneities for large wavelengths.

We study scenarios of parallel cyclic multiverses which allow for a different evolution of the physical constants, while having the same geometry. These universes are classically disconnected, but quantum-mechanically entangled. Applying the thermodynamics of entanglement, we calculate the temperature and the entropy of entanglement. It emerges that the entropy of entanglement is large at big bang and big crunch singularities of the parallel universes as well as at the maxima of the expansion of these universes. The latter seems to confirm earlier studies that quantum effects are strong at turning points of the evolution of the universe performed in the context of the timeless nature of the Wheeler-DeWitt equation and decoherence. On the other hand, the entropy of entanglement at big rip singularities is going to zero despite its presumably quantum nature. This may be an effect of total dissociation of the universe structures into infinitely separated patches violating the null energy condition. However, the temperature of entanglement is large/infinite at every classically singular point and at maximum expansion and seems to be a better measure of quantumness.

We observe a large fraction of circular polarization in radio emission from extensive air showers recorded during thunderstorms, much higher than in the emission from air showers measured during fair-weather circumstances. We show that the circular polarization of the air showers measured during thunderstorms can be explained by the change in the direction of the transverse current as a function of altitude induced by atmospheric electric fields. Thus by using the full set of Stokes parameters for these events, we obtain a good characterization of the electric fields in thunderclouds. We also measure a large horizontal component of the electric fields in the two events that we have analyzed.

Newly born massive magnetars are generally considered to be produced by binary neutron star (NS) mergers, which could give rise to short gamma-ray bursts (SGRBs). The strong magnetic fields and fast rotation of these magnetars make them promising sources for gravitational wave (GW) detection using ground based GW interferometers. Based on the observed masses of Galactic NS-NS binaries, by assuming different equations of state (EOSs) of dense matter, we investigate the stochastic gravitational wave background (SGWB) produced by an ensemble of newly born massive magnetars. The massive magnetar formation rate is estimated through: (i) the SGRB formation rate (hereafter entitled as MFR1); (ii) the NS-NS merger rate (hereafter entitled as MFR2). We find that for massive magnetars with masses $M_{mg}=2.4743M_{\odot }$, if EOS CDDM2 is assumed, the resultant SGWBs may be detected by the future Einstein Telescope (ET) even for MFR1 with minimal local formation rate, and for MFR2 with a local merger rate ${\dot{\rho }}_{\mathrm{c}}^{\mathrm{o}}(0)\lesssim 10{\mathrm{Mpc}}^{-3}{\mathrm{Myr}}^{-1}$. However, if EOS BSk21 is assumed, the SGWB may be detectable by the ET for MFR1 with the maximal local formation rate. Moreover, the background spectra show cutoffs at about 350 Hz in the case of EOS BSk21, and at 124 Hz for CDDM2, respectively. We suggest that if the cutoff at $\sim 100\mathrm{Hz}$ in the background spectrum from massive magnetars could be detected, then the quark star EOS CDDM2 seems to be favorable. Moreover, the EOSs, which present relatively small TOV maximum masses, would be excluded.

SuperCDMS SNOLAB will be a next-generation experiment aimed at directly detecting low-mass particles (with masses $\le 10\mathrm{GeV}/{\mathrm{c}}^2$) that may constitute dark matter by using cryogenic detectors of two types (HV and iZIP) and two target materials (germanium and silicon). The experiment is being designed with an initial sensitivity to nuclear recoil cross sections $\sim 1\times {10}^{-43}{\mathrm{cm}}^2$ for a dark matter particle mass of $1\mathrm{GeV}/{\mathrm{c}}^2$, and with capacity to continue exploration to both smaller masses and better sensitivities. The phonon sensitivity of the HV detectors will be sufficient to detect nuclear recoils from sub-GeV dark matter. A detailed calibration of the detector response to low-energy recoils will be needed to optimize running conditions of the HV detectors and to interpret their data for dark matter searches. Low-activity shielding, and the depth of SNOLAB, will reduce most backgrounds, but cosmogenically produced ${}^3\mathrm{H}$ and naturally occurring ${}^{32}\mathrm{Si}$ will be present in the detectors at some level. Even if these backgrounds are 10 times higher than expected, the science reach of the HV detectors would be over 3 orders of magnitude beyond current results for a dark matter mass of $1\mathrm{GeV}/{\mathrm{c}}^2$. The iZIP detectors are relatively insensitive to variations in detector response and backgrounds, and will provide better sensitivity for dark matter particles with masses $\gtrsim 5\mathrm{GeV}/{\mathrm{c}}^2$. The mix of detector types (HV and iZIP), and targets (germanium and silicon), planned for the experiment, as well as flexibility in how the detectors are operated, will allow us to maximize the low-mass reach, and understand the backgrounds that the experiment will encounter. Upgrades to the experiment, perhaps with a variety of ultra-low-background cryogenic detectors, will extend dark matter sensitivity down to the “neutrino floor,” where coherent scatters of solar neutrinos become a limiting background.

The free energy of a static quark-antiquark pair is obtained in an interacting dyon ensemble near the deconfinement temperature. Comparing the results with the noninteracting case, we observe that the string tension between the quark-antiquark pair increases for the interacting ensemble. As a result, the confinement temperature decreases.

We investigate the predictions for lepton flavor number violating processes in the context of a simple left-right symmetric theory. In this context neutrinos are Majorana fermions and their masses are generated at the quantum level through the Zee mechanism using the simplest Higgs sector. We show that the right-handed neutrinos are generically light and can give rise to large lepton flavor violating contributions to rare processes. We discuss the correlation between the collider constraints and the predictions for lepton flavor violating processes. We find that using the predictions for $\mu \to e\gamma$ and $\mu \to e$ conversion together with the collider signatures one could test this theory in the near future.

We present all the leading twist T-even transverse momentum dependent parton distributions (TMDs) in the light-front quark-diquark model (LFQDM) and study the relations among them. The model contains both the scalar and vector diquark with the light front wave functions modeled from the soft-wall AdS/QCD prediction. The $x-p_{\perp }^2$ factorization used in phenomenological extraction for TMDs is observed in this model. We present the results for the quark densities and the transverse shape of proton. The shape of the transversely polarized proton is shown to be nonspherical for nonzero transverse momentum. The scale evolution of both integrated and unintegrated TMDs are also presented in this paper.

We account for dynamical spin effects in the holographic light-front wavefunction of the pion in order to predict the mean charge radius, $\sqrt{⟨r_{\pi }^2⟩}$, the decay constant, $f_{\pi }$, the spacelike electromagnetic form factor, $F_{\pi }(Q^2)$, the twist-2 pion distribution amplitude and the photon-to-pion transition form factor $F_{\gamma \pi }(Q^2)$. Using a universal fundamental AdS/QCD scale, $\kappa =523\mathrm{MeV}$, and a constituent quark mass of 330 MeV, we find a remarkable improvement in describing all observables.

A measurement of the inclusive $pp\to t\overline{t}+X$ production cross section in the $\tau +\text{jets}$ final state using only the hadronic decays of the $\tau$ lepton is presented. The measurement is performed using $20.2{\mathrm{fb}}^{-1}$ of proton-proton collision data recorded at a center-of-mass energy of $\sqrt{s}=8\mathrm{TeV}$ with the ATLAS detector at the Large Hadron Collider. The cross section is measured via a counting experiment by imposing a set of selection criteria on the identification and kinematic variables of the reconstructed particles and jets, and on event kinematic variables and characteristics. The production cross section is measured to be ${\sigma }_{t\overline{t}}=239\pm 29\mathrm{pb}$, which is in agreement with the measurements in other final states and the theoretical predictions at this center-of-mass energy.

The B-model approach of topological string theory leads to difference equations by quantizing algebraic mirror curves. It is known that these quantum mechanical systems are solved by the refined topological strings. Recently, it was pointed out that the quantum eigenvalue problem for a particular Calabi–Yau manifold, known as local ${\mathbb{F}}_0$, is closely related to the Hofstadter problem for electrons on a two-dimensional square lattice. In this paper, we generalize this idea to a more complicated Calabi–Yau manifold. We find that the local ${\mathcal{B}}_3$ geometry, which is a three-point blow-up of local ${\mathbb{P}}^2$, is associated with electrons on a triangular lattice. This correspondence allows us to use known results in condensed matter physics to investigate the quantum geometry of the toric Calabi–Yau manifold.

We generalize the semiclassical treatment of graviton radiation to gravitational scattering at very large energies $\sqrt{s}\gg m_P$ and finite scattering angles ${\mathrm{\Theta }}_s$, so as to approach the collapse regime of impact parameters $b\simeq b_c\sim R\equiv 2G\sqrt{s}$. Our basic tool is the extension of the recently proposed, unified form of radiation to the Amati Ciafaloni Veneziano (ACV) reduced-action model and to its resummed-eikonal exchange. By superimposing that radiation all over eikonal scattering, we are able to derive the corresponding (unitary) coherent-state operator. The resulting graviton spectrum, tuned on the gravitational radius $R$, fully agrees with previous calculations for small angles ${\mathrm{\Theta }}_s\ll 1$ but, for sizeable angles ${\mathrm{\Theta }}_s(b)\le {\mathrm{\Theta }}_c=\mathcal{O}(1)$, acquires an exponential cutoff of the large $\omega R$ region, due to energy conservation, so as to emit a finite fraction of the total energy. In the approach-to-collapse regime of $b\to b_c^{+}$, we find a radiation enhancement due to large tidal forces, so that the whole energy is radiated off, with a large multiplicity $⟨N⟩\sim Gs\gg 1$ and a well-defined frequency cutoff of order $R^{-1}$. The latter corresponds to the Hawking temperature for a black hole of mass notably smaller than $\sqrt{s}$.

The semiclassical kinetic theory of Dirac particles in the presence of external electromagnetic fields and global rotation is established. To provide the Hamiltonian formulation of Dirac particles, a symplectic two-form which is a matrix in spin indices is proposed. The particle number and current densities for the Dirac particles are acquired in the helicity basis. Following a similar procedure, the semiclassical kinetic theory of the Weyl particles is accomplished. It is shown that the phase-space dynamics of the Weyl and Dirac particles is directly linked. The anomalous chiral effects due to the external electromagnetic fields and angular velocity of the frame are calculated.

We studied the leading area term of the entanglement entropy of the $\mathcal{N}=1$ supersymmetric $O(N)$ vector model in $2+1$ dimensions close to the line of the second order phase transition in the large $N$ limit. We found that the area term is independent of the varying interaction coupling along the critical line, unlike what is expected in a perturbative theory. Along the way, we studied noncommuting limits $n-1\to 0$ vs UV cutoff $r\to 0$ when evaluating the gap equation and found a match only when the appropriate counterterm is introduced and the coupling of which is chosen to take its fixed point value. As a bonus, we also studied fermionic Green functions in the conical background. We made the observation of a map between the problem and the relativistic hydrogen atom.

We investigate the metric perturbations of the restricted $f(R)$ theory of gravity in the cosmological context and explore the phenomenological implications of this model. We show that it is possible to construct a restricted model of gravity, in which the background equations are the same as the equations of motion which are derived from the Einstein-Hilbert action with the cosmological constant term. We argue that the deviation from the Einstein-Hilbert model emerges in the perturbed equations, for which we have a nonvanishing anisotropic stress. Further, with the help of the results of Planck data for the modified gravity, we obtain constraints on the parameters of the model.

The gravitational field of a laser pulse, although not detectable at the moment, has a special feature which continues to attract attention; cause and effect propagate with the same speed, the speed of light. One particular result of this feature is that the gravitational field of an emitted laser pulse and the gravitational effect of the emitter’s energy-momentum change are intimately entangled. In this article, a specific example of an emission process is considered: An atom, modeled as a point mass, emits two counter-propagating pulses. The corresponding curvature and the effect on massive and massless test particles is discussed. A comparison is made with the metric corresponding to a spherically symmetric massive object that isotropically emits radiation; the Vaidya metric.

A simple expression for calculating the classical potential in $D$-dimensional gravitational models is obtained through a method based on the generating functional. The prescription is then used as a mathematical tool to probe the conjecture that renormalizable higher-order gravity models—which are, of course, nonunitary—are endowed with a classical potential that is nonsingular at the origin. It is also shown that the converse of this statement is not true, which implies that the finiteness of the classical potential at the origin is a necessary but not sufficient condition for the renormalizability of the model. The systems we have utilized to verify the conjecture were fourth- and sixth-order gravity models in $D$ dimensions. A discussion about the polemic question related to the renormalizability of new massive gravity, which Oda claimed to be renormalizable in 2009 and which was shown to be nonrenormalizable by Muneyuki and Ohta three years later, is considered. We remark that the solution of this issue is straightforward if the aforementioned conjecture is employed. We point out that our analysis is restricted to local models in which the propagator has simple and real poles.