Some severe constraints on asymmetric dark matter are based on the scenario that certain types of weakly interacting massive particles can form mini-black holes inside neutron stars that can lead to their destruction. A crucial element for the realization of this scenario is that the black hole grows after its formation (and eventually destroys the star) instead of evaporating. The fate of the black hole is dictated by the two opposite mechanics, i.e., accretion of nuclear matter from the center of the star and Hawking radiation that tends to decrease the mass of the black hole. We study how the assumptions for the accretion rate can in fact affect the critical mass beyond which a black hole always grows. We also study to what extent degenerate nuclear matter can impede Hawking radiation due to the fact that emitted particles can be Pauli blocked at the core of the star.

Recently released Planck data favor a lower value of the Hubble constant and a higher value of the fraction matter density in the standard $\mathrm{\Lambda }\mathrm{CDM}$ model, which are discrepant with some of the low-redshift measurements. Within the context of this cosmology, we examine the consistency of the estimated values for the Hubble constant and fraction matter density with redshift tomography. Using the type Ia supernovae, Hubble parameter, baryon acoustic oscillation, and reduced cosmic microwave background data, which are divided into three bins, we find no statistical evidence for any tension in the three redshift bins.

Systems of self-gravitating fermions constitute a topic of great interest in astrophysics, due to the wide field of applications. In this paper, we consider the gravitational equilibrium of spherically symmetric Newtonian models of collisionless semidegenerate fermions. We construct numerical solutions by taking into account the effects of the anisotropy in the distribution function and considering the prevalence of tangential velocity. In this way, our models generalize the solutions obtained for isotropic Fermi-Dirac statistics. We also extend the analysis to equilibrium configurations in the classical regime and in the fully degenerate limit, recovering, for different levels of anisotropy, hollow equilibrium configurations obtained in the Maxwellian regime. Moreover, in the limit of full degeneracy, we find a direct expression relating the anisotropy with the mass of the particles composing the system.

We consider the holographic dark energy (HDE) model in the framework of the DGP braneworld with Granda-Oliveros infrared (IR) cutoff, $L={(\alpha \dot{H}+\beta H^2)}^{-1/2}$. With this choice for IR cutoff, we are able to derive evolution of the cosmological parameters such as the equation of state and the deceleration parameters, $w$ and $q$, as the functions of the redshift parameter $z$. As far as we know, most previous models of HDE presented in the literature, do not give analytically $\omega =\omega (z)$ and $q=q(z)$. We plot the evolution of these parameters versus $z$ and discuss that the results are compatible with the recent observations. With suitably choosing the parameters, this model can exhibit a transition from deceleration to the acceleration around $z\approx 0.6$. Then we suggest a correspondence between the quintessence and tachyon scalar fields and HDE in the framework of the DGP braneworld. This correspondence allows us to reconstruct the evolution of the scalar fields and the scalar potentials. We also investigate the stability of the presented model by calculating the squared sound speed, $v_s^2$, whose sign determines the stability of the model. Our study shows that $v_s^2$ could be positive provided the parameters of the model are chosen suitably. In particular, for $\alpha >1$, $\beta >0$, and $\alpha <1$, $\beta <0$, we have $v_s^2>0$ during the history of the Universe, and so the stable dark-energy-dominated universe can be achieved. This is in contrast to the HDE in standard cosmology, which is unstable against background perturbations and so cannot lead to a stable dark- energy-dominated universe.

In this paper we report on a search for short-duration gravitational wave bursts in the frequency range 64 Hz–1792 Hz associated with gamma-ray bursts (GRBs), using data from GEO 600 and one of the LIGO or Virgo detectors. We introduce the method of a linear search grid to analyze GRB events with large sky localization uncertainties, for example the localizations provided by the Fermi Gamma-ray Burst Monitor (GBM). Coherent searches for gravitational waves (GWs) can be computationally intensive when the GRB sky position is not well localized, due to the corrections required for the difference in arrival time between detectors. Using a linear search grid we are able to reduce the computational cost of the analysis by a factor of $\mathcal{O}(10)$ for GBM events. Furthermore, we demonstrate that our analysis pipeline can improve upon the sky localization of GRBs detected by the GBM, if a high-frequency GW signal is observed in coincidence. We use the method of the linear grid in a search for GWs associated with 129 GRBs observed satellite-based gamma-ray experiments between 2006 and 2011. The GRBs in our sample had not been previously analyzed for GW counterparts. A fraction of our GRB events are analyzed using data from GEO 600 while the detector was using squeezed-light states to improve its sensitivity; this is the first search for GWs using data from a squeezed-light interferometric observatory. We find no evidence for GW signals, either with any individual GRB in this sample or with the population as a whole. For each GRB we place lower bounds on the distance to the progenitor, under an assumption of a fixed GW emission energy of ${10}^{-2}\mathrm{M}\odot c^2$, with a median exclusion distance of 0.8 Mpc for emission at 500 Hz and 0.3 Mpc at 1 kHz. The reduced computational cost associated with a linear search grid will enable rapid searches for GWs associated with Fermi GBM events once the advanced LIGO and Virgo detectors begin operation.

The recently discovered 3.5 keV x-ray line from extragalactic sources may be evidence of dark matter scatterings or decays. We show that dark atoms can be the source of the emission, through their hyperfine transitions, which would be the analog of 21 cm radiation from a dark sector. We identify two families of dark atom models that match the x-ray observations and are consistent with other constraints. In the first, the hyperfine excited state is long lived compared to the age of the Universe, and the dark atom mass is relatively unconstrained; dark atoms could be strongly self-interacting in this case. In the second, the excited state is short lived, and viable models are parametrized by the value of the dark proton-to-electron mass ratio $R$: for $R={10}^2–{10}^4$, the dark atom mass is predicted to be in the range 350–1300 GeV, with fine structure constant ${\alpha }^{\prime }\cong 0.1–0.6$. In either class of models, the dark photon is expected to be massive with $m_{{\gamma }^{\prime }}\sim 1\mathrm{MeV}$ and decay into $e^{+}{e}^{-}$. Evidence for the model could come from direct detection of the dark atoms. In a natural extension of this framework, the dark photon could decay predominantly into invisible particles, for example, $\sim 0.5\mathrm{eV}$ sterile neutrinos, explaining the extra radiation degree of freedom recently suggested by data from BICEP2, while remaining compatible with big bang nucleosynthesis.

The $Q^2$-dependence of the sum of the electric and magnetic polarizabilities of the proton is calculated over the range $0\le Q^2\le 6{\mathrm{GeV}}^2$ using the generalized Baldin sum rule. Employing a parametrization of the $F_1$ structure function valid down to $Q^2=0.06{\mathrm{GeV}}^2$, the polarizabilities at the real photon point are found by extrapolating the results of finite $Q^2$ to $Q^2=0{\mathrm{GeV}}^2$. We determine the evolution over four-momentum transfer to be consistent with the Baldin sum rule using photoproduction data, obtaining $\alpha +\beta =13.7\pm 0.7\times {10}^{-4}{\mathrm{fm}}^3$.

High-energy Coulomb corrections to the parameters of the Molière multiple scattering theory are obtained. Numerical calculations are presented in the range of the nuclear charge number of the target atom $6⪕Z⪕92$. It is shown that these corrections have a large value for sufficiently heavy elements of the target material and should be taken into account in describing high-energy experiments with nuclear targets.

We analyze the constraints on $CP$-violating, flavor conserving two Higgs doublet models implied by measurements of Higgs boson properties at the Large Hadron Collider (LHC) and by the nonobservation of permanent electric dipole moments (EDMs) of molecules, atoms, and neutrons. We find that the LHC and EDM constraints are largely complementary, with the LHC studies constraining the mixing between the neutral $CP$-even states and the EDMs probing the effect of mixing between the $CP$-even and $CP$-odd scalars. Presently, the most stringent constraints are implied by the nonobservation of the ThO molecule EDM signal. Future improvements in the sensitivity of neutron and diamagnetic atom EDM searches could yield competitive or even more severe constraints. We analyze the quantitative impact of hadronic and nuclear theory uncertainties on the interpretation of the latter systems and conclude that these uncertainties cloud the impact of projected improvements in the corresponding experimental sensitivities.

Motivated by the gamma-ray excess observed from the region surrounding the Galactic Center, we explore particle dark matter models that could potentially account for the spectrum and normalization of this signal. Taking a model-independent approach, we consider an exhaustive list of tree-level diagrams for dark matter annihilation, and determine which could account for the observed gamma-ray emission while simultaneously predicting a thermal relic abundance equal to the measured cosmological dark matter density. We identify a wide variety of models that can meet these criteria without conflicting with existing constraints from direct detection experiments or the Large Hadron Collider (LHC). The prospects for detection in near future dark matter experiments and/or the upcoming 14 TeV LHC appear quite promising.

We present a method for resolving the combinatorial issues in the $t\overline{t}$ $\text{lepton}+\text{jets}$ events occurring at the Tevatron collider. By incorporating multiple information into an artificial neural network, we introduce a novel event reconstruction method for such events. We find that this method significantly reduces the number of combinatorial ambiguities. Compared to the classical reconstruction method, our method provides significantly higher purity with the same efficiency. We illustrate the reconstructed observables for the realistic top-quark mass and the forward-backward asymmetry measurements. A Monte Carlo study shows that our method provides meaningful improvements in the top-quark measurements using the same amount of data as other methods.

Borexino has been running since May 2007 at the Laboratori Nazionali del Gran Sasso laboratory in Italy with the primary goal of detecting solar neutrinos. The detector, a large, unsegmented liquid scintillator calorimeter characterized by unprecedented low levels of intrinsic radioactivity, is optimized for the study of the lower energy part of the spectrum. During Phase-I (2007–2010), Borexino first detected and then precisely measured the flux of the ${}^7\mathrm{Be}$ solar neutrinos, ruled out any significant day-night asymmetry of their interaction rate, made the first direct observation of the pep neutrinos, and set the tightest upper limit on the flux of solar neutrinos produced in the CNO cycle (carbon, nitrogen, oxigen) where carbon, nitrogen, and oxygen serve as catalysts in the fusion process. In this paper we discuss the signal signature and provide a comprehensive description of the backgrounds, quantify their event rates, describe the methods for their identification, selection, or subtraction, and describe data analysis. Key features are an extensive in situ calibration program using radioactive sources, the detailed modeling of the detector response, the ability to define an innermost fiducial volume with extremely low background via software cuts, and the excellent pulse-shape discrimination capability of the scintillator that allows particle identification. We report a measurement of the annual modulation of the ${}^7\mathrm{Be}$ neutrino interaction rate. The period, the amplitude, and the phase of the observed modulation are consistent with the solar origin of these events, and the absence of their annual modulation is rejected with higher than 99% C.L. The physics implications of Phase-I results in the context of the neutrino oscillation physics and solar models are presented.

We study the process $e^{+}{e}^{-}\to \psi (2S){\pi }^{+}{\pi }^{-}$ with initial-state-radiation events produced at the PEP-II asymmetric-energy collider. The data were recorded with the BABAR detector at center-of-mass energies at and near the $\mathrm{\Upsilon }(\mathrm{nS})$ ($n=2,3,4$) resonances and correspond to an integrated luminosity of $520{\mathrm{fb}}^{-1}$. We investigate the $\psi (2S){\pi }^{+}{\pi }^{-}$ mass distribution from 3.95 to $5.95\mathrm{GeV}/c^2$, and measure the center-of-mass energy dependence of the associated $e^{+}{e}^{-}\to \psi (2S){\pi }^{+}{\pi }^{-}$ cross section. The mass distribution exhibits evidence of two resonant structures. A fit to the $\psi (2S){\pi }^{+}{\pi }^{-}$ mass distribution corresponding to the decay mode $\psi (2S)\to J/\psi {\pi }^{+}{\pi }^{-}$ yields a mass value of $4340\pm 16(\text{stat})\pm 9(\text{syst})\mathrm{MeV}/c^2$ and a width of $94\pm 32(\text{stat})\pm 13(\text{syst})\mathrm{MeV}$ for the first resonance, and for the second a mass value of $4669\pm 21(\text{stat})\pm 3(\text{syst})\mathrm{MeV}/c^2$ and a width of $104\pm 48(\text{stat})\pm 10(\text{syst})\mathrm{MeV}$. In addition, we show the ${\pi }^{+}{\pi }^{-}$ mass distributions for these resonant regions.

We consider the perturbative consistency of inflationary models with features with effective field theory methods. By estimating the size of one-loop contributions to the three-point function, we find the energy scale where their contribution is of the same order of the tree-level amplitude. It is well known that beyond that scale, perturbative unitarity is lost and the theory is no more under theoretical control. Requiring that all the relevant energy scales of the problem are below this cutoff, we derive a strong upper bound on the sharpness of the feature, or equivalently on its characteristic time scale, which is independent on the amplitude of the feature itself. We point out that the sharp features that seem to provide better fits to the cosmic microwave background power spectrum are already outside this bound, questioning the consistency of the models that predict them.

We propose a one-parameter family of nonlinear covariant gauges which can be formulated as an extremization procedure that may be amenable to lattice implementation. At high energies, where the Gribov ambiguities can be ignored, this reduces to the Curci-Ferrari-Delbourgo-Jarvis gauges. We further propose a continuum formulation in terms of a local action which is free of Gribov ambiguities and avoids the Neuberger zero problem of the standard Faddeev-Popov construction. This involves an averaging over Gribov copies with a nonuniform weight, which introduces a new gauge-fixing parameter. We show that the proposed gauge-fixed action is perturbatively renormalizable in four dimensions and we provide explicit expressions of the renormalization factors at one loop. We discuss the possible implications of the present proposal for the calculation of Yang-Mills correlators.

We present a gauge mediation principle for beyond standard model theories where exact UV scale invariance is broken in a hidden sector. The relevant configurations are those in which the standard model and a hidden sector emanate from a scale invariant pair of UV theories that communicate only via gauge interactions. We compute the radiatively induced Higgs potential which contains logarithmic mass-squared terms that lead to unusual Higgs self-couplings. Its other couplings are unchanged.

We investigate Brownian motions of a particle coupled to vacuum fluctuations of a quantum field. The Unruh effect predicts that an observer in an accelerated motion sees the Minkowski vacuum as thermally excited. This addresses the problem of whether or not a thermal property appears in a perturbative random motion of a particle in an accelerated motion due to the coupling. We revisit this problem by solving the equation of motion of a particle coupled to vacuum fluctuations including the radiation reaction force. We compute a Fourier integral for the variance of the random velocity in a rigorous manner. Similarly, we consider a particle coupled to vacuum fluctuations in de Sitter spacetime motivated by the argument that an observer in de Sitter spacetime sees the Bunch-Davies vacuum as a thermally excited state with the Gibbons-Hawking temperature. Our investigation clarifies the condition that the energy equipartition relation arises in the Brownian motions of a particle.

The Weyl biconnection model manifests a natural framework to automatically produce the structure of the Galileon theory. It is shown that this framework can explain the scalar and vector Galileon as well as their interactions by generalizing the Weyl nonmetricity, and as such it can be interpreted as a geometrical realization for Galileons. The nonmetricity part enjoys a U(1) gauge invariance. The result is interestingly nontrivial since the structure of the Galileon theory appears spontaneously, and not by demanding the absence of the Ostrogradsky ghost. This fact suggests a possible deeper conceptual relation between the Weyl biconnection model and the absence of the Ostrogradsky ghost.

If binary black holes form following the successive core collapses of sufficiently massive binary stars, precessional dynamics may align their spins, ${\mathbf{S}}_{\mathbf{1}}$ and ${\mathbf{S}}_{\mathbf{2}}$, and the orbital angular momentum $\mathbf{L}$ into a plane in which they jointly precess about the total angular momentum $\mathbf{J}$. These spin orientations are known as spin-orbit resonances since ${\mathbf{S}}_{\mathbf{1}}$, ${\mathbf{S}}_{\mathbf{2}}$, and $\mathbf{L}$ all precess at the same frequency to maintain their planar configuration. Two families of such spin-orbit resonances exist, differentiated by whether the components of the two spins in the orbital plane are either aligned or antialigned. The fraction of binary black holes in each family is determined by the stellar evolution of their progenitors, so if gravitational-wave detectors could measure this fraction they could provide important insights into astrophysical formation scenarios for binary black holes. In this paper, we show that even under the conservative assumption that binary black holes are observed along the direction of $\mathbf{J}$ (where precession-induced modulations to the gravitational waveforms are minimized), the waveforms of many members of each resonant family can be distinguished from all members of the other family in events with signal-to-noise ratios $\rho \simeq 10$, typical of those expected for the first detections with Advanced LIGO and Virgo. We hope that our preliminary findings inspire a greater appreciation of the capability of gravitational-wave detectors to constrain stellar astrophysics and stimulate further studies of the distinguishability of spin-orbit resonant families in more expanded regions of binary black-hole parameter space.

We study the nature of the chiral transition for an effective theory with spontaneous breaking of symmetry, where charged bosons and fermions are subject to the effects of a constant external magnetic field. The problem is studied in terms of the relative intensity of the magnetic field with respect to the mass and the temperature. When the former is the smallest of the scales, we present a suitable method to obtain magnetic and thermal corrections up to ring order at high temperature. By these means, we solve the problem of the instability in the boson sector for these theories, where the squared masses—taken as functions of the order parameter—can vanish and even become negative. The solution is found by considering the screening properties of the plasma, encoded in the resummation of the ring diagrams at high temperature. We also study the case where the magnetic field is the intermediate of the three scales and explore the nature of the chiral transition as we vary the field strength, the coupling constants, and the number of fermions. We show that the critical temperature for the restoration of chiral symmetry monotonically increases from small to intermediate values of the magnetic field and that this temperature is always above the critical temperature for the case when the magnetic field is absent.