This work is driven by our curiosity about some basic questions in QCD: how is the energy of a moving hadron partitioned among different gauge-invariant sectors in the QCD Hamiltonian? How is the energy of a massless pion separated between quark and gluon sectors, particularly in the soft pion limit? Is it possible to decompose the celebrated Gell-Mann-Oakes-Renner (GOR) relation? To what extent can we justify the quark potential model from the field-theoretical mass decomposition for heavy quarkonium? Due to the limitations of contemporary nonperturbative tools, we do not yet know answers to these questions in realistic QCD. In this work, we take the ’t Hooft model (two-dimensional QCD in the large-$N$ limit) as a prototype that mimics some essential aspects of the true QCD. We investigate the gauge-invariant energy decomposition of a flavor-neutral meson that can carry an arbitrary momentum (including the stationary case), with the meson species ranging from the massless pion to bottomonium. All the aforementioned questions can be addressed satisfactorily within this model; in particular, some unexpected patterns related to the pion are discovered for the first time in two-dimensional QCD. We hope that our study can offer some useful clues and stimulation for future investigation of hadron energy decomposition in realistic QCD.

The most recent experimental data for all measured production and decay channels of the bottomoniumlike states $Z_b(10610)$ and $Z_b(10650)$ are analyzed simultaneously using solutions of the Lippmann-Schwinger equations which respect constraints from unitarity and analyticity. The interaction potential in the open-bottom channels $B^{(*)}{\overline{B}}^{*}+\mathrm{c}.\mathrm{c}.$ contains short-range interactions as well as a one-pion exchange. It is found that the long-range interaction does not affect the line shapes as long as only $S$ waves are considered. Meanwhile, the line shapes can be visibly modified once $D$ waves, mediated by the strong tensor forces from the pion exchange potentials, are included. However, in the fit they get balanced largely by a momentum dependent contact term that appears to be needed also to render the results for the line shapes independent of the cutoff. The resulting line shapes are found to be insensitive to various higher-order interactions included to verify stability of the results. Both $Z_b$ states are found to be described by the poles located on the unphysical Riemann sheets in the vicinity of the corresponding thresholds. In particular, the $Z_b(10610)$ state is associated with a virtual state residing just below the $B{\overline{B}}^{*}/\overline{B}{B}^{*}$ threshold while the $Z_b(10650)$ state most likely is a shallow state located just above the $B^{*}{\overline{B}}^{*}$ threshold.

We give a new description of classical Yang-Mills theory by coupling a two-dimensional chiral conformal field theory (which gives the tree-level S matrix of Yang-Mills theory at genus zero) to a background non-Abelian gauge field. The resulting model is solvable, and when the gravitational degrees of freedom are decoupled, the nonlinear Yang-Mills equations are imposed as an exact worldsheet anomaly cancellation condition. When gravitational modes are reinstated, we find gauge anomalies analogous to those appearing in heterotic string theory.

We compute the radiative quantum corrections to the critical exponents and amplitude ratios for $\mathrm{O}(N)$ $\lambda {\varphi }^4$ scalar high energy nonextensive $q$-field theories. We employ the field-theoretic renormalization group approach through six methods for evaluating the high energy nonextensive critical exponents up to next-to-leading order while the high energy nonextensive amplitude ratios are computed up to leading level by applying three methods. Later we generalize these high energy nonextensive finite loop order results for any loop level. We find that the high energy nonextensive critical exponents are the same when obtained through all the methods employed. The same fact occurs for the high energy nonextensive amplitude ratios. Furthermore, we show that these high energy nonextensive universal quantities are equal to their low energy extensive counterparts, thus showing that the nonextensivity is broken down at high energies.

We introduce a general method to construct, directly in configuration space, classes of dynamical systems invariant under generalizations of the Carroll and of the Galilei groups. The method does not make use of any nonrelativistic limiting procedure, although the starting point is a Lagrangian Poincaré invariant in the full space. It consists in considering a spacetime in $D+1$ dimensions and partitioning it in two parts, the first Minkowskian and the second Euclidean. The action consists of two terms that are separately invariant under the Minkowskian and Euclidean partitioning. One of those contains a system of lagrangian multipliers that confine the system to a subspace. The other term defines the dynamics of the system. The total lagrangian is invariant under the Carroll or the Galilei groups with zero central charge.

In order to explain the late-time cosmological acceleration, we propose a new pure geometric gravity based on Deser-Woodard theory [Phys. Rev. Lett. 99, 111301 (2007)], in which the expansion of a matter-dominated universe can be accelerating. This new theory behaves as well as general relativity in solar system and gravitational waves, which is an important improvement over Deser-Woodard nonlocal gravity. Especially, for the simplest case, theoretical considerations determine all the parameters that appear in the Lagrangian.

Assuming a simple form for the growth index $\gamma (z)$ depending on two parameters ${\gamma }_0\equiv \gamma (z=0)$ and ${\gamma }_1\equiv {\gamma }^{\prime }(z=0)$, we show that these parameters can be constrained using background expansion data. We explore systematically the preferred region in this parameter space. Inside general relativity we obtain that models with a quasistatic growth index and ${\gamma }_1\approx -0.02$ are favored. We find further the lower bounds ${\gamma }_0\gtrsim 0.53$ and ${\gamma }_1\gtrsim -0.15$ for models inside GR. Models outside GR having the same background expansion as $\mathrm{\Lambda }\mathrm{CDM}$ and arbitrary $\gamma (z)$ with ${\gamma }_0={\gamma }_0^{\mathrm{\Lambda }\mathrm{CDM}}$, satisfy $G_{\mathrm{eff},0}>G$ for ${\gamma }_1>{\gamma }_1^{\mathrm{\Lambda }\mathrm{CDM}}$, and $G_{\mathrm{eff},0}<G$ for ${\gamma }_1<{\gamma }_1^{\mathrm{\Lambda }\mathrm{CDM}}$. The first models will cross downwards the value $G_{\mathrm{eff}}=G$ on very low redshifts $z<0.3$, while the second models will cross upwards $G_{\mathrm{eff}}=G$ in the same redshift range. This makes the realization of such modified gravity models even more problematic.

While the global cosmological and local galactic abundance of dark matter is well established, its identity, physical size, and composition remain a mystery. In this paper, we analyze an important question of dark matter detectability through its gravitational interaction, using current and next generation gravitational-wave observatories to look for macroscopic (kilogram-scale or larger) objects. Keeping the size of the dark matter objects to be smaller than the physical dimensions of the detectors, and keeping their mass as a free parameter, we derive the expected event rates. For favorable choice of mass, we find that dark matter interactions could be detected in space-based detectors such as LISA at a rate of one per ten years. We then assume the existence of an additional Yukawa force between dark matter and regular matter. By choosing the range of the force to be comparable to the size of the detectors, we derive the levels of sensitivity to such a new force, which exceeds the sensitivity of other probes in a wide range of parameters. For sufficiently large Yukawa coupling strength, the rate of dark matter events can then exceed 10 per year for both ground- and space-based detectors. Thus, gravitational-wave observatories can make an important contribution to a global effort of searching for nongravitational interactions of dark matter.

We present a concept of a mirror for application in high-reflectivity low-noise instruments such as interferometers. The concept is based on an etalon with a metasurface (meta-etalon) on the front and a conventional multilayer stack on the rear surface. The etalon in combination with the metasurface enables a dedicated spatial weighing of the relevant thermal noise processes and by this a substantial reduction of the overall readout thermal noise. As examples, we illustrate the benefit of the proposed etalon for thermal noise in two applications: the test masses of the Einstein Telescope gravitational wave detector and a single-crystalline cavity for laser frequency stabilization. In the Einstein Telescope, the thermal noise of the etalon even at room temperature outperforms existing concepts for operation temperatures at 10 K. For the laser stabilization cavity, a reduction of the modified Allan deviation of an order of magnitude is predicted.

Gravitational-wave (GW) and electromagnetic (EM) signals from the merger of a neutron star (NS) and a black hole (BH) are a highly anticipated discovery. We present a simple formula, validated with 75 simulations, that distinguishes between potential merger outcomes and predicts the baryon mass left outside of the BH after merger. Our formula describes critical unexplored regimes: comparable masses with nonspinning BHs, and higher BH spins, and is essential in assessing whether events such as GW170817 could be NS-BH systems instead of NS-NS mergers.

We (re)consider the sensitivity of past (LSND) and future (${\mathrm{JSNS}}^2$) beam dump neutrino experiments to two models of MeV-scale pseudo-Dirac dark matter. Both LSND and ${\mathrm{JSNS}}^2$ are close (24–30 m) to intense sources of light neutral mesons which may decay to dark matter via interactions involving a light mediator or dipole operators. The dark matter can then scatter or decay inside of the nearby detector. We show that the higher beam energy of ${\mathrm{JSNS}}^2$ and resulting $\eta$ production can improve on the reach of LSND for light-mediator models with dark matter masses greater than $m_{\pi }/2$. Further, we find that both existing LSND and future ${\mathrm{JSNS}}^2$ measurements can severely constrain the viable parameter space for a recently proposed model of dipole dark matter which could explain the 3.5 keV excess reported in observations of stacked galaxy clusters and the Galactic center.

The direct observation of time reversal symmetry violation (TV) is important for the test of $CPT$ conservation and the Standard Model. In this paper, we study both time-dependent and time-independent genuine TV signals in entangled $D^0-{\overline{D}}^0$ pairs. A possible $CPT$-violation effect called the $\omega$ effect is also investigated. In the $C=-1$ entangled state, the asymmetries due to TV are calculated to be of the order of ${10}^{-5}$ to ${10}^{-4}$ within the Standard Model, but the modification due to the $\omega$ effect in the $C=-1$ states is found to be about 10%–30% when $|\omega |\sim {10}^{-4}$. This result is consistent with our Monte Carlo simulation, which implies that with $10^9$ to $10^{10}$ events, TV signals can be observed in the entangled $D^0-{\overline{D}}^0$ pairs, and the bound of $\omega \sim {10}^{-3}$ can be reached. The time-dependent and the time-independent asymmetries in the $C=-1$ $D^0-{\overline{D}}^0$ system provides a window to detect new physics such as the $\omega$ effect, although they are not easily observable.

We derive new Lorentz invariance and equation of motion relations between twist-three generalized parton distributions (GPDs) and moments in the parton transverse momentum, $k_T$, of twist-two generalized transverse momentum-dependent distributions (GTMDs), as a function of the parton longitudinal momentum fraction $x$. Although GTMDs in principle define the observables for partonic orbital motion, experiments that can unambiguously detect them appear remote at present. The relations presented here provide a solution to this impasse in that, e.g., the orbital angular momentum density is connected to directly measurable twist-three GPDs. Out of 16 possible equation of motion relations that can be written in the $T$-even sector, we focus on three helicity configurations that can be detected analyzing specific spin asymmetries: two correspond to longitudinal proton polarization and are associated with quark orbital angular momentum and spin-orbit correlations; the third, obtained for transverse proton polarization, is a generalization of the relation obeyed by the $g_2$ structure function. We also exhibit an additional relation connecting the off-forward extension of the Sivers function to an off-forward Qiu-Sterman term.

A search is presented for the four-body decay $B^0\to pp\overline{p}\overline{p}$ in a sample of 471 million $B\overline{B}$ pairs collected with the BABAR detector, operated at the SLAC PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider. The center-of-mass energy is 10.58 GeV. From a fit to the distribution of the energy-substituted mass $m_{\mathrm{ES}}$, the branching fraction $\mathcal{B}(B^0\to pp\overline{p}\overline{p})=(1.1\pm 0.5\pm 0.2)\times {10}^{-7}$ is extracted, where the first uncertainty is statistical and the second is systematic. The significance of the signal, including the systematic uncertainty, is 2.9 standard deviations. The upper limit on the branching fraction is determined to be $2.0\times {10}^{-7}$ at 90% confidence level.

The Kerr nature of a compact-object–coalescence remnant can be unveiled by observing multiple quasinormal modes in the post-merger signal. Current methods to achieve this goal rely on matching the data with a superposition of exponentially damped sinusoids with amplitudes fitted to numerical-relativity (NR) simulations of binary black-hole mergers. These models presume the ability to correctly estimate the time at which the gravitational-wave signal starts to be dominated by the quasinormal modes of a perturbed black hole. Here we show that this difficulty can be overcome by using multipolar inspiral-merger-ringdown waveforms, calibrated to NR simulations, as already developed within the effective-one-body formalism (EOBNR). We build a parameterized (nonspinning) EOBNR waveform model in which the quasinormal mode complex frequencies are free parameters (pEOBNR), and use Bayesian analysis to study its effectiveness in measuring quasinormal modes in GW150914, and in synthetic gravitational-wave signals of binary black holes injected in Gaussian noise. We find that using the pEOBNR model gives, in general, stronger constraints compared to the ones obtained when using a sum of damped sinusoids and using Bayesian model selection, we also show that the pEOBNR model can successfully be employed to find evidence for deviations from general relativity in the ringdown signal. Since the pEOBNR model properly includes time and phase shifts among quasinormal modes, it is also well suited to consistently combine information from several observations—e.g., we find on the order of $\sim 30$ GW150914-like binary black-hole events would be needed for Advanced LIGO and Virgo at design sensitivity to measure the fundamental frequencies of both the (2,2) and (3,3) modes, and the decay time of the (2,2) mode with an accuracy of $\lesssim 5\%$ at the $2\text{−}\sigma$ level, thus allowing to test the black hole’s no-hair conjecture.

A new definition of proper time, which may incorporate all of the fundamental interactions as well as the whole Poincaré group, is presented. The new proper time definition reduces to the usual one when neither interactions besides gravitational ones nor new group (such as Lorentz) transformations are considered. Physical implications of this new definition are discussed and a proposal for an experiment to check its validity is presented.

The braneworld model of gravity is well-known for several notable cosmological features such as self-acceleration originating from a geometric and not matter source, effective dark energy behavior with phantom characteristics but not leading to a big-rip singularity, rough resemblance to the $\mathrm{\Lambda }\mathrm{CDM}$ evolution, etc. The dynamical system tools usually allow us to obtain generic conclusions on the global dynamics of a system over a wide range of initial conditions. With this motivation, in order to recover the important features of the braneworld model from a more global perspective, here, we investigate the global cosmological dynamics of the braneworld model using dynamical system techniques. We first analyze the case where there is just a normal matter on the brane and then extend the analysis to the case with an extra scalar field also trapped on the brane. In the presence of a scalar field, potentials belonging to different classes are considered. The stability behavior of critical points is examined using linear stability analysis and when necessary center manifold theory as well as numerical perturbation techniques are also used. To understand the global dynamics of a dynamical system, we utilized the Poincaré compactification method to capture the properties of all possible critical points. Applying dynamical system analysis, we found that brane gravity is consistent with observed actions of the Universe. In particular, our analysis shows that important cosmological behaviors like the long-lasting matter-dominated era, late time acceleration as well as the avoidance of big-rip singularity can be realized in brane gravity for a wide range of initial conditions.

Motivated by the apparent discrepancy between cosmic microwave background measurements of the Hubble constant and measurements from Type-Ia supernovae, we construct a model for dark energy with equation of state $w=p/\rho <-1$, violating the null energy condition. Naive canonical models of so-called “phantom” dark energy require a negative scalar kinetic term, resulting in a Hamiltonian unbounded from below and associated vacuum instability. We construct a scalar field model for dark energy with $w<-1$, which nonetheless has a Hamiltonian bounded from below in the comoving reference frame, i.e., in the rest frame of the fluid. We demonstrate that the solution is a cosmological attractor, and find that early-time cosmological boundary conditions consist of a “frozen” scalar field, which relaxes to the attractor solution once the dark energy component dominates the cosmological energy density. We consider the model in an arbitrary choice of gauge, and find that, unlike the case of comoving gauge, the fluid Hamiltonian is in fact unbounded from below in the reference frame of a highly boosted observer, corresponding to a nonlinear gradient instability. We discuss this in the context of general NEC-violating perfect fluids, for which this instability is a general property.

We present the calculation of thermal noise in interferometric gravitational-wave detectors due to the thermal fluctuations of the beam splitter (BS). This work makes use of a recently developed method of analysis of thermal noise in mirrors from first principles, based on the fluctuation dissipation theorem. The evaluation of BS thermal noise is carried out for the two different gravitational wave observatories, GEO600 and the Advanced Laser Interferometer Gravitational Wave Observatory (aLIGO). The analysis evaluates thermal noise from both the substrate and the optical reflective and antireflective stacks located on the BS surface. We demonstrate that the fluctuations of both reflecting and antireflecting surfaces significantly contribute to the total thermal noise of the BS. The oscillating intensity pattern couples small-scale distortions of the surface to the overall phase readout, and therefore increases the overall thermal noise. In the case of aLIGO, the BS contribution is with 0.3% negligibly small. At a frequency of 500 Hz, the BS causes about 10% of GEO600’s sensitivity limit. BS noise impairs the feasible sensitivity of the GEO-HF design proposal by about 50%.

Effective neutrino-quark generalized interactions are entirely determined by Lorentz invariance, so they include all possible four-fermion nonderivative Lorentz structures. They contain neutrino-quark nonstandard interactions as a subset, but span over a larger set that involves effective scalar, pseudoscalar, axial and tensor operators. Using recent COHERENT data, we derive constraints on the corresponding couplings by considering scalar, vector and tensor quark currents and assuming no lepton flavor dependence. We allow for mixed neutrino-quark Lorentz couplings and consider two types of scenarios in which: (i) one interaction at the nuclear level is present at a time, (ii) two interactions are simultaneously present. For scenarios (i) our findings show that scalar interactions are the most severely constrained, in particular for pseudoscalar-scalar neutrino-quark couplings. In contrast, tensor and nonstandard vector interactions still enable for sizable effective parameters. We find as well that an extra vector interaction improves the data fit when compared with the result derived assuming only the standard model contribution. In scenarios (ii) the presence of two interactions relaxes the bounds and opens regions in parameter space that are otherwise closed, with the effect being more pronounced in the scalar-vector and scalar-tensor cases. We point out that barring the vector case, our results represent the most stringent bounds on effective neutrino-quark generalized interactions for mediator masses of order $\sim 1\mathrm{GeV}$. They hold as well for larger mediator masses, case in which they should be compared with limits from neutrino deep-inelastic scattering data.