In this work, we study the merger of two neutron stars with a gravitational mass of $1.4M_{\odot }$ each, employing the Shen-Horowitz-Teige equation of state. This equation of state is a corner case, allowing the formation of a stable neutron star with the given total baryonic mass of $3.03M_{\odot }$. We investigate in unprecedented detail the structure of the remnant, in particular the mass distribution, the thermal structure, and the rotation profile. We also compute fluid trajectories both inside the remnant and those relevant for the formation of the disk. We find a peanut-shaped fluid flow inside the remnant following a strong $m=2$ perturbation. Moreover, the flow is locally compressive, causing the appearance of dynamic hot spots. Further, we introduce new diagnostic measures that are easy to implement in numeric simulations and that allow one to quantify mass and compactness of merger remnants in a well-defined way. As in previous studies of supra- and hypermassive stars, we find a remnant with a slowly rotating core and an outer envelope rotating at nearly Keplerian velocity. We compute a Tolman-Oppenheimer-Volkoff star model which agrees well with that of the remnant in the core, while the latter possesses extensive outer layers rotating close to Kepler velocity. Finally, we extract the gravitational wave signal and discuss the detectability with modern observatories. This study has implications for the interpretation of gravitational wave detections from the postmerger phase and is relevant for short gamma-ray burst models.

Assuming that the AdS/CFT prescription is valid in the case of noncausal backgrounds, we apply it to the simplest possible eternal time machine solution in ${\mathrm{AdS}}_3$ based on two conical defects moving around their center of mass along a circular orbit. Closed timelike curves in this space-time extend all the way to the boundary of ${\mathrm{AdS}}_3$, violating causality of the boundary field theory. By use of the geodesic approximation we address the issue of self-consistent dynamics of the dual $1+1$ dimensional field theory when causality is violated, and calculate the two-point retarded Green function. It has a nontrivial analytical structure both at negative and positive times, providing us with an intuition on how an interacting quantum field could behave once causality is broken.

The knowledge of the properties of the different exact solutions modeling binary systems is a necessary step toward the classification of physically suitable solutions and its corresponding limits of applicability. In the present paper, we perform an analysis of the geodesics around two counter-rotating Kerr-Newman black holes endowed with opposite electric charges, which achieve equilibrium by means of a strut between their constituents. We find that bounded and unbounded orbits are possible. However, test particles may cross between the black holes only if their angular momentum equals zero; otherwise, there exists a repulsive potential, which prohibits such orbits. Two important aspects are pointed out for these trajectories: (i) the motion of photons is affected once it has crossed the strut, and (ii) massive particles exhibit oscillatory motion, as a first analog of the Sitnikov problem in general relativity. The radius of the innermost stable circular orbit as a function of the physical parameters of the black holes is also investigated.

In a previous paper, we developed tools for studying the horizon geometry of a Kerr black hole that is tidally distorted by a binary companion using techniques that require large mass ratios but can be applied to any bound orbit and allow for arbitrary black hole spin. We now apply these tools to generic Kerr black hole orbits. This allows us to investigate horizon dynamics: the tidal field perturbing the horizon’s geometry varies over a generic orbit, with significant variations for eccentric orbits. Many of the features of the horizon’s behavior found previously carry over to the dynamical case in a natural way. In particular, we find significant offsets between the applied tide and the horizon’s response. This leads to bulging in the horizon’s geometry which can lag or lead the orbit, depending upon the hole’s rotation and the orbit’s geometry. An interesting and apparently new feature we find are small-amplitude, high-frequency oscillations in the horizon’s response. We have not been able to identify a mechanism for producing these oscillations but find that they appear most clearly when rapidly rotating black holes are distorted by very strong-field orbits.

Noise hunting is a critical requirement for realizing design sensitivity of a detector, and consequently, noise origins and its features have been revealed partially. Among the noise sources to be hunted, sources of nonlinearly correlated noise, such up-conversion noise, are hard to find and can limit the sensitivity of gravitational wave searches with advanced detectors. We propose using a correlation analysis method called maximal information coefficient (MIC) to find both nonlinear and linear correlations. We apply MIC to the scattered light noise correlated between the seismic activity and the strain signal, which limited the sensitivity of the Virgo detector during the first science run. The results show that MIC can find nonlinearly correlated noise more efficiently than the Pearson correlation method. When the data is linearly correlated, the efficiency of the Pearson method and MIC is comparable. On the other hand, when the data is known to be nonlinearly correlated, MIC finds the correlation while the Pearson method fails completely.

In light of the recent 750 GeV diphoton excesses reported by the ATLAS and CMS collaborations, we investigate the possibility of explaining this excess using the minimal dilaton model. We find that this model is able to explain the observed excess with the presence of additional top partner(s), with the same charge as the top quark, but with mass in the TeV region. First, we constrain model parameters using in addition to the 750 GeV diphoton signal strength, precision electroweak tests, single top production measurements, as well as Higgs signal strength data collected in the earlier runs of the LHC. In addition we discuss interesting phenomenology that could arise in this model, relevant for future runs of the LHC.

Why is natural supersymmetry neither detected nor ruled out to date? To answer this question we use the Bayesian approach where the emphasis in finding prior-independent features within broader and minimally biased frames is taken as the guiding principle. The 20-parameter minimal supersymmetric standard model (MSSM) global fits to subjective naturalness indicate the existence of a prior-independent upper bound on the pseudoscalar Higgs boson mass $m_A$ as a function of $\tan \beta$, the ratio of the vacuum expectation values of MSSM Higgs doublets. For a 30-parameter MSSM this implies that $m_A\lesssim 3\mathrm{TeV}$ and $\tan \beta \lesssim 25$ at 95% Bayesian confidence. Removing the contradictory subjectiveness within the electroweak fine-tuning measure leads to finding the naturalness line, $m_A\sim \frac{1}{\sqrt{2}}{m}_Z\tan \beta$, that reduces by one the number of MSSM Higgs sector free parameters.

The quark orbital angular momentum component of proton spin, $L_q$, can be defined in QCD as the integral of a Wigner phase space distribution weighting the cross product of the quark’s transverse position and momentum. It can also be independently defined from the operator product expansion for the off-forward Compton amplitude in terms of a twist-three generalized parton distribution. We provide an explicit link between the two definitions, connecting them through their dependence on partonic intrinsic transverse momentum. Connecting the definitions provides the key for correlating direct experimental determinations of $L_q$ and evaluations through lattice QCD calculations. The direct observation of quark orbital angular momentum does not require transverse spin polarization but can occur using longitudinally polarized targets.

The partition function of a relativistic invariant quantum field theory is expressed by its vacuum energy calculated on a spatial manifold with one dimension compactified to a 1-sphere $S^1(\beta )$, whose circumference $\beta$ represents the inverse temperature. Explicit expressions for the usual energy density and pressure in terms of the energy density on the partially compactified spatial manifold ${\mathbb{R}}^2\times S^1(\beta )$ are derived. To make the resulting expressions mathematically well defined a Poisson resummation of the Matsubara sums as well as an analytic continuation in the chemical potential are required. The new approach to finite-temperature quantum field theories is advantageous in a Hamilton formulation since it does not require the usual thermal averages with the density operator. Instead, the whole finite-temperature behavior is encoded in the vacuum wave functional on the spatial manifold ${\mathbb{R}}^2\times S^1(\beta )$. We illustrate this approach by calculating the pressure of a relativistic Bose and Fermi gas and reproduce the known results obtained from the usual grand canonical ensemble. As a first nontrivial application we calculate the pressure of Yang-Mills theory as a function of the temperature in a quasiparticle approximation motivated by variational calculations in Coulomb gauge.

We corroborate the previously applied spectral approach to compute the vacuum polarization energy of string configurations in models similar to the standard model of particle physics. The central observation underlying this corroboration is the existence of a particular global isospin transformation of the string configuration. Under this transformation the single particle energies of the quantum fluctuations are invariant, while the inevitable implementation of regularization and renormalization requires operations that are not invariant. We verify numerically that all such variances eventually cancel, and that the vacuum polarization energy obtained in the spectral approach is indeed gauge invariant.

It is generally believed that, when matter collapses to form a black hole, the complete information about the initial state of the matter cannot be retrieved by future asymptotic observers, through local measurements. This is contrary to the expectation from a unitary evolution in quantum theory and leads to (a version of) the black hole information paradox. Classically, nothing else, apart from mass, charge, and angular momentum is expected to be revealed to such asymptotic observers after the formation of a black hole. Semiclassically, black holes evaporate after their formation through the Hawking radiation. The dominant part of the radiation is expected to be thermal and hence one cannot know anything about the initial data from the resultant radiation. However, there can be sources of distortions which make the radiation nonthermal. Although the distortions are not strong enough to make the evolution unitary, these distortions carry some part of information regarding the in-state. In this work, we show how one can decipher the information about the in-state of the field from these distortions. We show that the distortions of a particular kind—which we call nonvacuum distortions—can be used to fully reconstruct the initial data. The asymptotic observer can do this operationally by measuring certain well-defined observables of the quantum field at late times. We demonstrate that a general class of in-states encode all their information content in the correlation of late time out-going modes. Further, using a $1+1$ dimensional dilatonic black hole model to accommodate backreaction self-consistently, we show that observers can also infer and track the information content about the initial data, during the course of evaporation, unambiguously. Implications of such information extraction are discussed.

The “trousers” spacetime is a pair of flat two-dimensional cylinders (“legs”) merging into a single one (“trunk”). In spite of its simplicity this spacetime has a few features (including, in particular, a naked singularity in the “crotch”) each of which is presumably unphysical, but for none of which a mechanism is known able to prevent its occurrence. Therefore, it is interesting and important to study the behavior of the quantum fields in such a space. Anderson and DeWitt were the first to consider the free scalar field in the trousers spacetime. They argued that the crotch singularity produces an infinitely bright flash, which was interpreted as evidence that the topology of space is dynamically preserved. Similar divergencies were later discovered by Manogue, Copeland, and Dray who used a more exotic quantization scheme. Later yet the same result obtained within a somewhat different approach led Sorkin to the conclusion that the topological transition in question is suppressed in quantum gravity. In this paper I show that the Anderson-DeWitt divergence is an artifact of their choice of the Fock space. By choosing a different one-particle Hilbert space one gets a quantum state in which the components of the stress-energy tensor (SET) are bounded in the frame of a free-falling observer.

The computation of the renormalized stress-energy tensor or ${⟨{\varphi }^2⟩}_{\text{ren}}$ in curved spacetime is a challenging task, at both the conceptual and technical levels. Recently we developed a new approach to compute such renormalized quantities in asymptotically flat curved spacetimes, based on the point-splitting procedure. Our approach requires the spacetime to admit some symmetry. We already implemented this approach to compute ${⟨{\varphi }^2⟩}_{\text{ren}}$ in a stationary spacetime using $t$ splitting, namely splitting in the time-translation direction. Here we present the angular-splitting version of this approach, aimed for computing renormalized quantities in a general (possibly dynamical) spherically symmetric spacetime. To illustrate how the angular-splitting method works, we use it here to compute ${⟨{\varphi }^2⟩}_{\text{ren}}$ for a quantum massless scalar field in Schwarzschild background, in various quantum states (Boulware, Unruh, and Hartle-Hawking states). We find excellent agreement with the results obtained from the $t$-splitting variant and also with other methods. Our main goal in pursuing this new mode-sum approach was to enable the computation of the renormalized stress-energy tensor in a dynamical spherically symmetric background, e.g. an evaporating black hole. The angular-splitting variant presented here is most suitable to this purpose.

In the accretion flow of a fluid, its velocity may transit from subsonic to supersonic. The point at which such a transition occurs is called the sonic point and is often mathematically special. We consider the steady-state and spherically symmetric accretion problem of an ideal photon gas in general static spherically symmetric spacetimes, neglecting backreaction. Our main result is that the equation of state (EOS) of an ideal photon gas leads to a correspondence between its sonic point and the photon sphere of the spacetime in general situations. Moreover, we also show that in spite of the dependence of the EOS on the dimension of spacetime, this correspondence holds for spacetimes of arbitrary dimensions.

Weak lensing convergence peaks are a promising tool to probe nonlinear structure evolution at late times, providing additional cosmological information beyond second-order statistics. Previous theoretical and observational studies have shown that the cosmological constraints on ${\mathrm{\Omega }}_m$ and ${\sigma }_8$ are improved by a factor of up to $\approx 2$ when peak counts and second-order statistics are combined, compared to using the latter alone. We study the origin of lensing peaks using observational data from the $154{\mathrm{deg}}^2$ Canada-France-Hawaii Telescope Lensing Survey. We found that while high peaks (with height $\kappa >3.5{\sigma }_{\kappa }$, where ${\sigma }_{\kappa }$ is the rms of the convergence $\kappa$) are typically due to one single massive halo of $\approx 10^{15}{M}_{\odot }$, low peaks ($\kappa \lesssim {\sigma }_{\kappa }$) are associated with constellations of 2–8 smaller halos ($\lesssim 10^{13}{M}_{\odot }$). In addition, halos responsible for forming low peaks are found to be significantly offset from the line of sight towards the peak center (impact parameter $\gtrsim$ their virial radii), compared with $\approx 0.25$ virial radii for halos linked with high peaks, hinting that low peaks are more immune to baryonic processes whose impact is confined to the inner regions of the dark matter halos. Our findings are in good agreement with results from the simulation work by Yang et al. [Phys. Rev. D 84, 043529 (2011)].

We deliver a lattice study of $\rho$ resonance parameters with $p$-wave $\pi \pi$ scattering phases, which are extracted by finite-size methods at one center-of-mass frame and four moving frames for six lattice ensembles from the MILC Collaboration with pion masses ranging from 346 to 176 MeV. The effective range formula is applied to describe the scattering phases as a function of the energy covering the resonance region; this allows us to extract $\rho$ resonance parameters and to investigate the quark-mass dependence. Lattice studies with three flavors of Asqtad-improved staggered fermions enable us to use the moving-wall source technique on large lattice spatial dimensions ($L=64$) and small light $u/d$ quarks. Numerical computations are carried out at two lattice spacings, $a\approx 0.12$ and 0.09 fm.

We interpret the potential observation of the 750 GeV diphoton resonance at the LHC in models, in which an $SU(2)$ isospin-singlet scalar boson mixes with the standard model (SM) Higgs boson through an angle $\alpha$. Allowing the singlet scalar boson to have renormalizable couplings to vectorlike leptons and quarks and introducing sizable decay width of the 750 GeV diphoton resonance into non-SM particles such as dark matters, we can explain the large production cross section $\sigma (H_2)\times B(H_2\to \gamma \gamma )$ as well as the apparent large total width of the boson without conflicts from the results obtained by previous global fits to the SM Higgs boson data.

We study a model of interacting spinless fermions in a one dimensional lattice with supersymmetry (SUSY). The Hamiltonian is given by the anticommutator of two supercharges $Q$ and $Q^{†}$, each of which is comprised solely of fermion operators and possesses one adjustable parameter $g$. When the parameter $g$ vanishes, the model is identical to the one studied by Nicolai [H. Nicolai, J. Phys. A 9, 1497 (1976)], where the zero-energy ground state is exponentially degenerate. On the other hand, in the large-$g$ limit the model reduces to the free-fermion chain with a four-fold degenerate ground state. We show that for finite chains SUSY is spontaneously broken when $g>0$. We also rigorously prove that for sufficiently large $g$ the ground-state energy density is nonvanishing in the infinite-volume limit. We further analyze the nature of the low-energy excitations by employing various techniques such as rigorous inequalities, exact numerical diagonalization, and renormalization group method with bosonization. The analysis reveals that the low-energy excitations are described by massless Dirac fermions (or Thirring fermions more generally), which can be thought of as Nambu-Goldstone fermions from the spontaneous SUSY breaking.