One of the striking features of general relativity is that the Einstein equation is implied by the Clausius relation imposed on a small patch of locally constructed causal horizon. The extension of this thermodynamic derivation of the field equation to more general theories of gravity has been attempted many times in the last two decades. In particular, equations of motion for minimally coupled higher-curvature theories of gravity, but without the derivatives of curvature, have previously been derived using a thermodynamic reasoning. In that derivation the horizon slices were endowed with an entropy density whose form resembles that of the Noether charge for diffeomorphisms, and was dubbed the Noetheresque entropy. In this paper, we propose a new entropy density, closely related to the Noetheresque form, such that the field equation of any diffeomorphism-invariant metric theory of gravity can be derived by imposing the Clausius relation on a small patch of local causal horizon.

In this paper we address the problem of dark energy oscillations in the context of mimetic $F(R)$ gravity with potential. The issue of dark energy oscillations can be a problem in some models of ordinary $F(R)$ gravity, and a remedy that can make the oscillations milder is to introduce additional modifications in the functional form of the $F(R)$ gravity. As we demonstrate, the power-law modifications are not necessary in the mimetic $F(R)$ case, and by appropriately choosing the mimetic potential and the Lagrange multiplier, it is possible to make the oscillations almost vanish at the end of the matter domination era and during the late-time acceleration era. We examine the behavior of the dark energy equation of state parameter and of the total effective equation of state parameter as functions of the redshift, and we compare the resulting picture with the ordinary $F(R)$ gravity case. As we also show that the present day values of the dark energy equation of state parameter and of the total effective equation of state parameter are in better agreement with the observational data, in comparison to the ordinary $F(R)$ gravity case. Finally, we study the evolution of the growth factor as a function of the redshift for all the mimetic models we use.

We consider a model of the classical spinning particle in which the coadjoint orbits of the Poincaré group are parametrized by two pairs of canonically conjugate four-vectors, one representing the standard position and momentum variables, and the other encoding the spinning degrees of freedom. This “dual phase space model” is shown to be a consistent theory of both massive and massless particles and allows for coupling to background fields such as electromagnetism. The on-shell action is derived and shown to be a sum of two terms, one associated with motion in spacetime, and the other with motion in “spin space.” Interactions between spinning particles are studied, and a necessary and sufficient condition for consistency of a three-point vertex is established.

We investigate the impact of spatial topology in $3+1$-dimensional causal dynamical triangulations (CDT) by performing numerical simulations with toroidal spatial topology instead of the previously used spherical topology. In the case of spherical spatial topology, we observed in the so-called phase C an average spatial volume distribution $n(t)$ which after a suitable time redefinition could be identified as the spatial volume distribution of the four-sphere. Imposing toroidal spatial topology, we find that the average spatial volume distribution $n(t)$ is constant. By measuring the covariance matrix of spatial volume fluctuations, we determine the form of the effective action. The difference compared to the spherical case is that the effective potential has changed such that it allows a constant average $n(t)$. This is what we observe and this is what one would expect from a minisuperspace GR action, where only the scale factor is kept as dynamical variable. Although no background geometry is put in by hand, the full quantum theory of CDT is also with toroidal spatial toplogy able to identify a classical background geometry around which there are well-defined quantum fluctuations.

The “memory effect” is the permanent change in the relative separation of test particles resulting from the passage of gravitational radiation. We investigate the memory effect for a general, spatially flat Friedmann-Lemaître-Robertson-Walker (FLRW) cosmology by considering the radiation associated with emission events involving particle-like sources. We find that if the resulting perturbation is decomposed into scalar, vector, and tensor parts, only the tensor part contributes to memory. Furthermore, the tensor contribution to memory depends only on the cosmological scale factor at the source and observation events, not on the detailed expansion history of the universe. In particular, for sources at the same luminosity distance, the memory effect in a spatially flat FLRW spacetime is enhanced over the Minkowski case by a factor of ($1+z$).

We study a class of nonlocal, action-based, and purely gravitational models. These models seek to describe a cosmology in which inflation is driven by a large, bare cosmological constant that is screened by the self-gravitation between the soft gravitons that inflation rips from the vacuum. Inflation ends with the Universe poised on the verge of gravitational collapse, in an oscillating phase of expansion and contraction that should lead to rapid reheating when matter is included. After the attainment of a hot, dense Universe the nonlocal screening terms become constant as the Universe evolves through a conventional phase of radiation domination. The onset of matter domination triggers a much smaller antiscreening effect that could explain the current phase of acceleration.

The $B$-mode polarization in the cosmic microwave background (CMB) anisotropies at large angular scales provides compelling evidence for the primordial gravitational waves (GWs). It is often stated that a discovery of the GWs establishes the quantum fluctuation of vacuum during the cosmic inflation. Since the GWs could also be generated by source fields, however, we need to check if a sizable signal exists due to such source fields before reaching a firm conclusion when the $B$ mode is discovered. Source fields of particular types can generate non-Gaussianity (NG) in the GWs. Testing statistics of the $B$ mode is a powerful way of detecting such NG. As a concrete example, we show a model in which gauge field sources chiral GWs via a pseudoscalar coupling and forecast the detection significance at the future CMB satellite LiteBIRD. Effects of residual foregrounds and lensing $B$ mode are both taken into account. We find the $B$-mode bispectrum “BBB” is in particular sensitive to the source-field NG, which is detectable at LiteBIRD with a $>3\sigma$ significance. Therefore the search for the BBB will be indispensable toward unambiguously establishing quantum fluctuation of vacuum when the $B$ mode is discovered. We also introduced the Minkowski functional to detect the NGs. While we find that the Minkowski functional is less efficient than the harmonic-space bispectrum estimator, it still serves as a useful cross-check. Finally, we also discuss the possibility of extracting clean information on parity violation of GWs and new types of parity-violating observables induced by lensing.

Massive scalar fields can form long-lived configurations around black holes. These configurations, dubbed quasibound states, have been studied both in the linear and nonlinear regimes. In this paper, we show that quasibound states can form in a dynamical scenario in which the mass of the black hole grows significantly due to the capture of infalling matter. We solve the Klein-Gordon equation numerically in spherical symmetry, mimicking the evolution of the spacetime through a sequence of analytic Schwarzschild black hole solutions of increasing mass. It is found that the frequency of oscillation of the quasibound states decreases as the mass of the black hole increases. In addition, accretion leads to an increase of the exponential decay of the scalar field energy. We compare the black hole mass growth rates used in our study with estimates from observational surveys and extrapolate our results to values of the scalar field masses consistent with models that propose scalar fields as dark matter in the universe. We show that, even for unrealistically large mass accretion rates, quasibound states around accreting black holes can survive for cosmological time scales. Our results provide further support to the intriguing possibility of the existence of dark matter halos based on (ultralight) scalar fields surrounding supermassive black holes in galactic centers.

We examine the development and detectability of the $m=1$ instability in the remnant of binary neutron star mergers. The detection of the gravitational mode associated with the $m=1$ degree of freedom could potentially reveal details of the equation of state. We analyze the postmerger epoch of simulations of both equal- and nonequal-mass neutron star mergers using three realistic, microphysical equations of state and neutrino cooling. Our studies show such an instability develops generically and within a short dynamical time to strengths that are comparable to or stronger than the $m=2$ mode, which is the strongest during the early postmerger stage. We estimate the signal to noise ratio that might be obtained for the $m=1$ mode and discuss the prospects for observing this signal with available Earth-based detectors. Because the $m=1$ occurs at roughly half the frequency of the more powerful $m=2$ signal and because it can potentially be long lived, targeted searches could be devised to observe it. We estimate that with constant amplitude direct detection of the mode could occur up to a distance of roughly 14 Mpc, whereas a search triggered by the inspiral signal could extend this distance to roughly 100 Mpc.

We show that if the propagating speed of gravitational waves (GWs) gradually diminishes during inflation, the power spectrum of primordial GWs will be strongly blue, while that of the primordial scalar perturbation may be unaffected. We also illustrate that such a scenario is actually a disformal dual to the superinflation, but it does not have the ghost instability. The blue tilt obtained is $0<n_T\lesssim 1$, which may significantly boost the stochastic GW background at the frequency band of Advanced LIGO/Virgo, as well as the space-based detectors.

Various new physics models, e.g., theories of compositeness, can accommodate the color singlet excited leptons that interact with the leptons, quarks, leptoquarks, etc. A particular type of excited lepton, which can be produced through the four-fermion interaction with a lepton and quark-antiquark (or lepton-antilepton) pair, we call a leptomeson. These new particles may contribute to a variety of experimental anomalies such as the discrepancy in the muon $g-2$. We propose that the leptomesons also can generate the baryon asymmetry that explains the imbalance in ordinary matter and antimatter in the observable Universe. We consider the two types of scenarios for this baryogenesis via leptogenesis to occur from either leptomeson oscillations or decays. Neither possibility contradicts the small masses of the observable neutrinos and the proton stability. Moreover, they can be relevant for the near-future collider experiments and do not suffer from the gravitino problem.

We study the sensitivity of the proposed SHiP experiment to the $LQD$ operator in $R$-parity violating supersymmetric theories. We focus on single neutralino production via rare meson decays and the observation of downstream neutralino decays into charged mesons inside the SHiP decay chamber. We provide a generic list of effective operators and decay width formulas for any ${\lambda }^{\prime }$ coupling and show the resulting expected SHiP sensitivity for a widespread list of benchmark scenarios via numerical simulations. We compare this sensitivity to expected limits from testing the same decay topology at the LHC with ATLAS.

We present an analysis of the dynamics of two-flavor QCD in the vacuum. Special attention is paid to the transition from the high-energy quark-gluon regime to the low-energy regime governed by hadron dynamics. This is done within a functional renormalization group approach to QCD amended by dynamical hadronization techniques. These techniques allow us to describe conveniently the transition from the perturbative high-energy regime to the nonperturbative low-energy limit without suffering from a fine-tuning of model parameters. In the present work, we apply these techniques to two-flavor QCD with physical quark masses and show how the dynamics of the dominant low-energy degrees of freedom emerge from the underlying quark-gluon dynamics.

Previously, a matrix model of the region near the transition temperature, in the “semi”quark gluon plasma, was developed for the theory of $SU(3)$ gluons without quarks. In this paper we develop a chiral matrix model applicable to QCD by including dynamical quarks with $2+1$ flavors. This requires adding a nonet of scalar fields, with both parities, and coupling these to quarks through a Yukawa coupling, $y$. Treating the scalar fields in mean field approximation, the effective Lagrangian is computed by integrating out quarks to one loop order. As is standard, the potential for the scalar fields is chosen to be symmetric under the flavor symmetry of $SU(3{)}_L\times SU(3{)}_R\times Z(3{)}_A$, except for a term linear in the current quark mass, $m_{\mathrm{qk}}$. In addition, at a nonzero temperature $T$ it is necessary to add a new term, $\sim m_{\mathrm{qk}}{T}^2$. The parameters of the gluon part of the matrix model are identical to those for the pure glue theory without quarks. The parameters in the chiral matrix model are fixed by the values, at zero temperature, of the pion decay constant and the masses of the pions, kaons, $\eta$, and ${\eta }^{\prime }$. The temperature for the chiral crossover at $T_{\chi }=155\mathrm{MeV}$ is determined by adjusting the Yukawa coupling $y$. We find reasonable agreement with the results of numerical simulations on the lattice for the pressure and related quantities. In the chiral limit, besides the divergence in the chiral susceptibility there is also a milder divergence in the susceptibility between the Polyakov loop and the chiral order parameter, with critical exponent $\beta -1$. We compute derivatives with respect to a quark chemical potential to determine the susceptibilities for baryon number, the ${\chi }_{2n}$. Especially sensitive tests are provided by ${\chi }_4-{\chi }_2$ and by ${\chi }_6$, which changes in sign about $T_{\chi }$. The behavior of the susceptibilities in the chiral matrix model strongly suggests that as the temperature increases from $T_{\chi }$, that the transition to deconfinement is significantly quicker than indicated by the measurements of the (renormalized) Polyakov loop on the lattice.

We construct an improved implementation for combining transverse-momentum-dependent (TMD) factorization and collinear factorization. TMD factorization is suitable for low transverse momentum physics, while collinear factorization is suitable for high transverse momenta and for a cross section integrated over transverse momentum. The result is a modified version of the standard $W+Y$ prescription traditionally used in the Collins-Soper-Sterman (CSS) formalism and related approaches. We further argue that questions regarding the shape and $Q$ dependence of the cross sections at lower $Q$ are largely governed by the matching to the $Y$ term.

We propose to study at the Large Hadron Collider (LHC) the inclusive production of a pair of hadrons (a “dihadron” system) in a kinematics where two detected hadrons with high transverse momenta are separated by a large interval of rapidity. This process has much in common with the widely discussed Mueller-Navelet jet production and can also be used to access the dynamics of hard proton-parton interactions in the Regge limit. For both processes large contributions enhanced by logarithms of energy can be resummed in perturbation theory within the Balitsky-Fadin-Kuraev-Lipatov (BFKL) formalism with next-to-leading logarithmic accuracy. The experimental study of dihadron production would provide an additional clear channel to test the BFKL dynamics. We present here the first theoretical predictions for cross sections and azimuthal angle correlations of the dihadrons produced with LHC kinematics.

We report the discovery of ${\mathrm{\Xi }}_c(3055{)}^0$, observed by its decay into the final-state $\mathrm{\Lambda }{D}^0$, and present the first observation and evidence of the decays of ${\mathrm{\Xi }}_c(3055{)}^{+}$ and ${\mathrm{\Xi }}_c(3080{)}^{+}$ into $\mathrm{\Lambda }{D}^{+}$. We also perform a combined analysis of the $\mathrm{\Lambda }{D}^{+}$ with the ${\mathrm{\Sigma }}_c^{++}{K}^{-}$ and ${\mathrm{\Sigma }}_c^{*++}{K}^{-}$ decay modes to measure the ratios of branching fractions, masses and widths with improved accuracy. We measure the ratios of branching fractions $\mathcal{B}({\mathrm{\Xi }}_c(3055{)}^{+}\to \mathrm{\Lambda }{D}^{+})/\mathcal{B}({\mathrm{\Xi }}_c(3055{)}^{+}\to {\mathrm{\Sigma }}_c^{++}{K}^{-})=5.09\pm 1.01\pm 0.76$, $\mathcal{B}({\mathrm{\Xi }}_c(3080{)}^{+}\to \mathrm{\Lambda }{D}^{+})/\mathcal{B}({\mathrm{\Xi }}_c(3080{)}^{+}\to {\mathrm{\Sigma }}_c^{++}{K}^{-})=1.29\pm 0.30\pm 0.15$, and $\mathcal{B}({\mathrm{\Xi }}_c(3080{)}^{+}\to {\mathrm{\Sigma }}_c^{*++}{K}^{-})/\mathcal{B}({\mathrm{\Xi }}_c(3080{)}^{+}\to {\mathrm{\Sigma }}_c^{++}{K}^{-})=1.07\pm 0.27\pm 0.04$, where the uncertainties are statistical and systematic. The analysis is performed using a $980{\mathrm{fb}}^{-1}$ data sample collected with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider.

Holographic models of QCD, collectively known as anti-de Sitter/QCD, have been proven useful in deriving several properties of hadrons. One particular feature well reproduced by such models is the Regge trajectories, both for mesons and glueballs. We focus on scalar and tensor glueballs and derive an effective theory for the Pomeron by analytic continuation along the leading trajectory from the tensor glueball. It then follows that the Pomeron, as the tensor glueball itself, should possess a two-index polarization tensor, inherited from the graviton. The three-graviton interaction is deduced from the Einstein-Hilbert action. Using this structure in the cross section of double-Pomeron production of the tensor glueball, we calculate certain angular distributions of production and compare them with those from the CERN WA102 experiment. We find that the agreement is very good for the $f_2(2300)$ tensor glueball candidate. At the same time, other tensor states—such as $f_2(1270)$ and $f_2^{\prime }(1520)$—have completely different distributions, which we interpret as a consequence of the fact that they are not glueballs and thus, in our model, unrelated to the gravitational excitations, which are dual to spin-2 glueballs.

We provide a gauge-covariant decomposition of the Yang-Mills field with the exceptional gauge group $G(2)$, which extends the field decomposition proposed by Cho, Duan-Ge, and Faddeev-Niemi for the $SU(N)$ Yang-Mills field. As an application of the decomposition, we derive a new expression of the non-Abelian Stokes theorem for the Wilson loop operator in an arbitrary representation of $G(2)$. The resulting new form is used to define gauge-invariant magnetic monopoles in the $G(2)$ Yang-Mills theory. Moreover, we obtain the quantization condition to be satisfied by the resulting magnetic charge. The method given in this paper is general enough to be applicable to any semisimple Lie group other than $SU(N)$ and $G(2)$.

A small body orbiting a black hole follows a trajectory that, at leading order, is a geodesic of the black hole spacetime. Much effort has gone into computing “self-force” corrections to this motion, arising from the small body’s own contributions to the system’s spacetime. Another correction to the motion arises from coupling of the small body’s spin to the black hole’s spacetime curvature. Spin-curvature coupling drives a precession of the small body, and introduces a “force” (relative to the geodesic) which shifts the small body’s worldline. These effects scale with the small body’s spin at leading order. In this paper, we show that the equations which govern spin-curvature coupling can be analyzed with a frequency-domain decomposition, at least to leading order in the small body’s spin. We show how to compute the frequency of precession along generic orbits, and how to describe the small body’s precession and motion in the frequency domain. We illustrate this approach with a number of examples. This approach is likely to be useful for understanding spin coupling effects in the extreme mass ratio limit, and may provide insight into modeling spin effects in the strong field for nonextreme mass ratios.