Recent work has shown that scalar fields around black holes can form long-lived, quasistationary configurations surviving for cosmological time scales. Scalar fields thus cannot be discarded as viable candidates for dark matter halo models in galaxies around central supermassive black holes (SMBHs). One hypothesized formation scenario of most SMBHs at high redshift is the gravitational collapse of supermassive stars (SMSs) with masses of $\sim {10}^5{\mathrm{M}}_{\odot }$. Any such scalar field configurations must survive the gravitational collapse of a SMS in order to be a viable model of physical reality. To check for the postcollapse survival of these configurations and to follow the dynamics of the black hole–scalar field system we present in this paper the results of a series of numerical relativity simulations of gravitationally collapsing, spherically symmetric stars surrounded by self-gravitating scalar fields. We use an ideal fluid equation of state with adiabatic index $\mathrm{\Gamma }=4/3$ which is adequate to simulate radiation-dominated isentropic SMSs. Our results confirm the existence of oscillating, long-lived, self-gravitating scalar field configurations around nonrotating black holes after the collapse of the stars.

Advanced gravitational wave interferometric detectors will operate at their design sensitivity with nearly $\sim 1\mathrm{MW}$ of laser power stored in the arm cavities. Such large power may lead to the uncontrolled growth of acoustic modes in the test masses due to the transfer of optical energy to the mechanical modes of the arm cavity mirrors. These parametric instabilities have the potential to significantly compromise the detector performance and control. Here we present the design of “acoustic mode dampers” that use the piezoelectric effect to reduce the coupling of optical to mechanical energy. Experimental measurements carried on an Advanced LIGO-like test mass have shown a tenfold reduction in the amplitude of several mechanical modes, thus suggesting that this technique can greatly mitigate the impact of parametric instabilities in advanced detectors.

We discuss the future prospects of heavy neutrino searches at next generation lepton colliders. In particular, we focus on the planned electron-positron colliders, operating in two different beam modes, namely, $e^{+}{e}^{-}$ and $e^{-}{e}^{-}$. In the $e^{+}{e}^{-}$ beam mode, we consider various production and decay modes of the heavy neutrino ($N$), and find that the final state with $e+2j+\cancel{E}$, arising from the $e^{+}{e}^{-}\to N\nu$ production mode, is the most promising channel. However, since this mode is insensitive to the Majorana nature of the heavy neutrinos, we also study a new production channel $e^{+}{e}^{-}\to N{e}^{\pm }{W}^{\mp }$, which leads to a same-sign dilepton plus four jet final state, thus directly probing the lepton number violation in $e^{+}{e}^{-}$ colliders. In the $e^{-}{e}^{-}$ beam mode, we study the prospects of the lepton number violating process of $e^{-}{e}^{-}\to W^{-}{W}^{-}$, mediated by a heavy Majorana neutrino. We use both cut-based and multivariate analysis techniques to make a realistic calculation of the relevant signal and background events, including detector effects for a generic linear collider detector. We find that with the cut-based analysis, the light-heavy neutrino mixing parameter $|V_{eN}{|}^2$ can be probed down to $\sim 10^{-4}$ at 95% C.L. for the heavy neutrino mass up to 400 GeV or so at $\sqrt{s}=500\mathrm{GeV}$ with $100{\mathrm{fb}}^{-1}$ of integrated luminosity. For smaller mixing values, we show that a multivariate analysis can improve the signal significance by up to an order of magnitude. These limits will be at least an order of magnitude better than the current best limits from electroweak precision data, as well as the projected limits from $\sqrt{s}=14\mathrm{TeV}$ LHC.

We apply a color glass $\text{condensate}+\text{nonrelativistic}$ QCD ($\mathrm{CGC}+\mathrm{NRQCD}$) framework to compute $J/\psi$ production in deuteron-nucleus collisions at RHIC and proton-nucleus collisions at the LHC. Our results match smoothly at high $p_{\perp }$ to a next-to-leading order perturbative $\mathrm{QCD}+\mathrm{NRQCD}$ computation. Excellent agreement is obtained for $p_{\perp }$ spectra at the RHIC and LHC for central and forward rapidities, as well as for the normalized ratio $R_{\mathrm{pA}}$ of these results to spectra in proton-proton collisions. In particular, we observe that the $R_{\mathrm{pA}}$ data are strongly bounded by our computations of the same for each of the individual NRQCD channels; this result provides strong evidence that our description is robust against uncertainties in initial conditions and hadronization mechanisms.

The effects of electric field polarizations on pair production from a vacuum are investigated numerically by employing the real-time Dirac-Heisenberg-Wigner formalism. For few-cycle fields, it is found that the interference pattern in momentum spectra is absent and the circular distortion of the momentum distribution becomes more apparent with an increase of the polarization. For multicycle fields, it is found that the interference effects in momentum spectra are obvious. And as the polarization increases, the momentum distribution is split into two parts in the momentum $q_y$ direction first and then two separated parts are connected into a ring. The effects of polarizations on the number density of created particles exhibits two different characteristics. For a small laser frequency, the particle number density decreases with the polarization, while for a large laser frequency, the relation between them is sensitive to the field frequency nonlinearly. Some interpretations for the results obtained in this study are provided, which are expected to be valuable for understanding pair production in complex fields and also helpful for the study of strong-field ionization.

The global structure of the family of Kerr–de Sitter spacetimes is reexamined. Taking advantage of the natural length scale set by the cosmological constant $\mathrm{\Lambda }>0$, conditions on the parameters $(\mathrm{\Lambda },M,a^2)$ have been found, so that a Kerr–de Sitter spacetime either describes a black hole with well-separated horizons, or describes degenerate configurations where two or more horizons coincide. As long as the rotation parameter $a^2$ is subject to the constraint $a^2\mathrm{\Lambda }\ll 1$, and the mass parameter $M$ is subject to $a^2[1+O(a^2\mathrm{\Lambda }{)}^2)]<M^2<\frac{1}{9\mathrm{\Lambda }}[1+2a^2\mathrm{\Lambda }+O(a^2\mathrm{\Lambda }{)}^2)]$, then a Kerr–de Sitter spacetime with parameters in these ranges describes a black hole possessing an inner horizon separated from an outer horizon and the hole is embedded within a pair of cosmological horizons. Still for $a^2\mathrm{\Lambda }\ll 1$, but assuming that either $M^2>\frac{1}{9\mathrm{\Lambda }}[1+2a^2\mathrm{\Lambda }+O(a^2\mathrm{\Lambda }{)}^2)]$ or $M^2<a^2[1+O(a^2\mathrm{\Lambda }{)}^2)]$, the Kerr–de Sitter spacetime describes a ringlike singularity enclosed by two cosmological horizons. A Kerr–de Sitter spacetime may also describe configurations where the inner, the outer and one of the cosmological horizons coincide. However, we found that this coalescence occurs provided $M^2\mathrm{\Lambda }\sim 1$ and due to the observed smallness of $\mathrm{\Lambda }$, these configurations are probably irrelevant in astrophysical settings. Extreme black holes, i.e. black holes where the inner horizon coincides with the outer black hole horizon, are also admitted. We have found that in the limit $M^2\mathrm{\Lambda }\ll 1$ and $a^2\mathrm{\Lambda }\ll 1$, extreme black holes occur, provided $a^2=M^2(1+O(\mathrm{\Lambda }{M}^2))$. Finally a coalescence between the outer and the cosmological horizon, although in principle possible, is likely to be unimportant at the astrophysical level, since this requires $M^2\mathrm{\Lambda }\sim 1$. Our analysis shows that as far as the structure of the horizons is concerned, the family of Kerr–de Sitter spacetimes exhibits similar structure to the Reissner–Nordstrom–de Sitter family of spacetimes.

We analyze the universal properties of a new two-dimensional quantum gravity model defined in terms of locally causal dynamical triangulations. Measuring the Hausdorff and spectral dimensions of the dynamical geometrical ensemble, we find numerical evidence that the continuum limit of the model lies in a new universality class of two-dimensional quantum gravity theories, inequivalent to both Euclidean and causal dynamical triangulations. The presence of significant finite-size effects, which are present even at the largest volumes investigated, prevents us from reaching a more definite conclusion.

We study the stability of anti–de Sitter (AdS) spacetime to spherically symmetric perturbations of a real scalar field in general relativity. Further, we work within the context of the “two time framework” (TTF) approximation, which describes the leading nonlinear effects for small amplitude perturbations, and is therefore suitable for studying the weakly turbulent instability of AdS—including both collapsing and noncollapsing solutions. We have previously identified a class of quasiperiodic (QP) solutions to the TTF equations, and in this paper we analyze their stability. We show that there exist several families of QP solutions that are stable to linear order, and we argue that these solutions represent islands of stability in TTF. We extract the eigenmodes of small oscillations about QP solutions, and we use them to predict approximate recurrence times for generic noncollapsing initial data in the full (non-TTF) system. Alternatively, when sufficient energy is driven to high-frequency modes, as occurs for initial data far from a QP solution, the TTF description breaks down as an approximation to the full system. Depending on the higher order dynamics of the full system, this often signals an imminent collapse to a black hole.

Dark matter particles can be captured by the Sun with rates that depend on the dark matter mass and the DM-nucleon cross section. However, for masses below $\sim 3.3\mathrm{GeV}$, the captured dark matter particles evaporate, leading to an equilibrium where the rate of captured particles is equal to the rate of evaporating ones. Unlike dark matter particles from the halo, the evaporating dark matter particles have velocities that are not limited to values below the escape velocity of the Galaxy. Despite the fact that high velocities are exponentially suppressed, I demonstrate here that current underground detectors have the possibility to probe/constrain low dark matter parameter space by (not)-observing the high energy tail of the evaporating dark matter particles from the Sun. I also show that the functional form of the differential rate of counts with respect to the recoil energy in Earth-based detectors can identify precisely the mass and the cross section of the dark matter particle in this case.

Jet finding is a type of optimization problem, where hadrons from a high-energy collision event are grouped into jets based on a clustering criterion. As three interesting examples, one can form a jet cluster that (i) optimizes the overall jet four-vector, (ii) optimizes the jet axis, or (iii) aligns the jet axis with the jet four-vector. In this paper, we show that these three approaches to jet finding, despite being philosophically quite different, can be regarded as descendants of a mother optimization problem. For the special case of finding a single cone jet of fixed opening angle, the three approaches are genuinely identical when defined appropriately, and the result is a stable cone jet with the largest value of a quantity $J$. This relationship is only approximate for cone jets in the rapidity-azimuth plane, as used at the Large Hadron Collider, though the differences are mild for small radius jets.

The neutrino mass matrix has remnant $CP$ symmetry expressed in terms of the lepton mixing matrix, and vice versa the remnant $CP$ transformations allow us to reconstruct the mixing matrix. We study the scenario that all four remnant $CP$ transformations are preserved by the neutrino mass matrix. The most general parametrization of remnant $CP$ transformations is presented. The lepton mixing matrix is completely fixed by the remnant $CP$, and its explicit form is derived. The necessary and sufficient condition for conserved Dirac $CP$ violating phase is found. If the Klein four flavor symmetry generated by the postulated remnant $CP$ transformations arises from a finite flavor symmetry group, the phenomenologically viable lepton flavor mixing would be the trimaximal pattern, both Dirac $CP$ phase ${\delta }_{CP}$ and Majorana phase ${\alpha }_{31}$ are either 0 or $\pi$ while another Majorana phase ${\alpha }_{21}$ is a rational multiple of $\pi$. These general results are confirmed to be true in the case that the finite flavor symmetry group is $\mathrm{\Delta }(6n^2)$.

Understanding the spectral and flavor composition of the astrophysical neutrino flux responsible for the recently observed ultrahigh-energy events at IceCube is of great importance for both astrophysics and particle physics. We perform a statistical likelihood analysis to the three-year IceCube data and derive the allowed range of the spectral index and flux normalization for various well-motivated physical flavor compositions at the source. While most of the existing analyses so far assume the flavor composition of the neutrinos at an astrophysical source to be (1:2:0), it seems rather unnatural to assume only one type of source, once we recognize the possibility of at least two physical sources. Bearing this in mind, we entertain the possibility of a two-component source for the analysis of IceCube data. It appears that our two-component hypothesis explains some key features of the data better than a single-component scenario; i.e. it addresses the apparent energy gap between 400 TeV and about 1 PeV and easily accommodates the observed track-to-shower ratio. Given the extreme importance of the flavor composition for the correct interpretation of the underlying astrophysical processes as well as for the ramification for particle physics, this two-component flux should be tested as more data is accumulated.

Motivated by the theoretical possibility of floating orbits and the potential to contribute extra constraints on alternative theories, in this paper we derive the self-force equation for a small compact object moving on an accelerated world line in a background spacetime which is a solution of the coupled gravitational and scalar field equations of scalar-tensor theory. In the Einstein frame, the coupled field equations governing the perturbations sourced by the particle share the same form as the field equations for perturbations of a scalarvac spacetime in general relativity, with both falling under the general class of hyperbolic field equations studied in [1]. Here, we solve the field equations formally in terms of retarded Green functions, which have explicit representations as Hadamard forms in the neighborhood of the world line. Using a quasilocal expansion of the Hadamard form, we derive the regular solutions in Fermi normal coordinates according to the Detweiler-Whiting prescription. To compute the equation of motion, we parametrize the world line by the particle’s mass and “charge,” which we define in terms of the original Jordan frame mass, its derivative, and the parameter which translates the proper time in the Jordan frame to the Einstein frame. These parameters depend on the value of the background scalar field and its self-field corrections. The equation of motion which follows from the regular fields strongly resembles the equation for the self-force acting on a charged, massive particle in a scalarvac geometry of general relativity. Unlike the scalar vacuum scenario, the charge parameter in the scalar-tensor self-force equation is time variable and leading to additional local and tail terms. We also provide evolution equations for the world line parameters under the influence of the self-fields.

We study the semileptonic decays of $D_s^{+}$, $D^{+}$, and $D^0$ mesons into the light scalar mesons [$f_0(500)$, $K_0^{*}(800)$, $f_0(980)$, and $a_0(980)$] and the light vector mesons [$\rho (770)$, $\omega (782)$, $K^{*}(892)$, and $\varphi (1020)$]. With the help of a chiral unitarity approach in coupled channels, we compute the branching fractions for scalar meson processes of the semileptonic $D$ decays in a simple way. Using current known values of the branching fractions, we make predictions for the branching fractions of the semileptonic decay modes with other scalar and vector mesons. Furthermore, we calculate the ${\pi }^{+}{\pi }^{-}$, $\pi \eta$, $\pi K$, and $K^{+}{K}^{-}$ invariant mass distributions in the semileptonic decays of $D$ mesons, which will help us clarify the nature of the light scalar mesons.

Electric fields can thread a classical Einstein-Rosen bridge. Maldacena and Susskind have recently suggested that in a theory of dynamical gravity the entanglement of ordinary perturbative quanta should be viewed as creating a quantum version of an Einstein-Rosen bridge between the particles, or a “quantum wormhole.” We demonstrate within low-energy effective field theory that there is a precise sense in which electric fields can also thread such quantum wormholes. We define a nonperturbative “wormhole susceptibility” that measures the ease of passing an electric field through any sort of wormhole. The susceptibility of a quantum wormhole is suppressed by powers of the $U(1)$ gauge coupling relative to that for a classical wormhole but can be made numerically equal with a sufficiently large amount of entangled matter.

The integrated Sachs-Wolfe (ISW) effect predicts additional anisotropies in the cosmic microwave background (CMB) due to time variation of the gravitational potential when the expansion of the Universe is not matter dominated. The ISW effect is therefore expected in the early Universe, due to the presence of relativistic particles at recombination, and in the late Universe, when dark energy starts to dominate the expansion. Deviations from the standard picture can be parametrized by $A_{e\mathrm{ISW}}$ and $A_{l\mathrm{ISW}}$, which rescale the overall amplitude of the early and late ISW effects. Analyzing the most recent CMB temperature spectra from the Planck 2015 release, we detect the presence of the early ISW at high significance with $A_{e\mathrm{ISW}}=1.06\pm 0.04$ at 68% C.L. and an upper limit for the late ISW of $A_{l\mathrm{ISW}}<1.1$ at 95% C.L. The inclusion of the recent polarization data from the Planck experiment results in $A_{e\mathrm{ISW}}=0.999\pm 0.028$ at 68% C.L., in better agreement with the value $A_{e\mathrm{ISW}}=1$ of a standard cosmology. When considering the recent detections of the late ISW coming from correlations between CMB temperature anisotropies and weak lensing, a value of $A_{l\mathrm{ISW}}=0.85\pm 0.21$ is predicted at 68% C.L., showing $4\sigma$ evidence. We discuss the stability of our result in the case of an extra relativistic energy component parametrized by the effective neutrino number $N_{\mathrm{eff}}$ and of a CMB lensing amplitude $A_{\mathrm{L}}$.

The vector mode of cosmological perturbation theory imprints characteristic signals on the weak lensing signals such as curl and B modes which are never imprinted by the scalar mode. However, the vector mode is neglected in the standard first-order cosmological perturbation theory since it only has a decaying mode. This situation changes if the cosmological perturbation theory is expanded up to second order. The second-order vector and tensor modes are inevitably induced by the product of the first-order scalar modes. We study the effect of the second-order vector mode on the weak lensing curl and B modes. We find that the curl mode induced by the second-order vector mode is comparable to that induced by the primordial gravitational waves with the tensor-to-scalar ratio $r=0.1$ at $\ell \approx 200$. In this case, the curl mode induced by the second-order vector mode dominates at $\ell >200$. Furthermore, the B-mode cosmic shear induced by the second-order vector mode dominates on almost all scales. However, we find that the observational signatures of the second-order vector and tensor modes cannot exceed the expected noise of ongoing and upcoming weak lensing measurements. We conclude that the curl and B modes induced by the second-order vector and tensor modes are unlikely to be detected in future experiments.