Various theories beyond the Standard Model predict new particles with masses in the sub-eV range with very weak couplings to ordinary matter which can possess spin-dependent couplings to electrons and nucleons. Present laboratory constraints on exotic spin-dependent interactions with pseudoscalar and axial couplings for exchange boson masses between meV and eV are very poor compared to constraints on spin-independent interactions in the same mass range arising from spin-0 and spin-1 boson exchange. It is therefore interesting to analyze in a general way how one can use the strong experimental bounds on spin-independent interactions to also constrain spin-dependent interactions by considering higher-order exchange processes. The exchange of a pair of bosons between two fermions with spin-dependent couplings will possess contributions which flip spins twice and thereby generate a polarization-independent interaction energy which can add coherently between two unpolarized objects. In this paper we derive the dominant long-range contributions to the interaction energy between two nonrelativistic spin-$1/2$ Dirac fermions from double exchange of spin-0 and spin-1 bosons proportional to couplings of the form $g_P^4$, $g_S^2{g}_P^2$, and $g_V^2{g}_A^2$. Our results for $g_P^4$ are in agreement with previous calculations that have appeared in the literature. We demonstrate the usefulness of this analysis to constrain spin-dependent couplings by presenting the results of a reanalysis of data from a short-range gravity experiment to derive an improved constraint on $(g_P^N{)}^2$, the pseudoscalar coupling for nucleons, in the range between 40 and $200\mu \mathrm{m}$ of about a factor of 5 compared to previous limits. We hope that the expressions derived in this work will be employed by other researchers in the future to evaluate whether or not they can constrain exotic spin-dependent interactions from spin-independent measurements. The spin-independent contribution from 2-boson exchange with axial vector couplings of the form $g_A^4$ requires special treatment and will be explored in another paper.

We calculate radiative corrections to the quark quasidistribution in lattice perturbation theory at one loop to leading orders in the lattice spacing. We also consider one-loop corrections in continuum Euclidean space. We find that the infrared behavior of the corrections in Euclidean and Minkowski space are different. We explore features of momentum loop integrals and demonstrate why loop corrections from the lattice perturbation theory and Euclidean continuum do not correspond with their Minkowski brethren, and comment on a recent suggestion for transcending the differences in the results. Further, we examine the role of the lattice spacing $a$ and of the $r$ parameter in the Wilson action in these radiative corrections.

Paying attention to conformal invariance as the invariance under local transformations of units of measure, we take a conformal-invariant quantum field as a quantum matter theory in which one has the freedom to choose the values of units of mass, length, and time arbitrarily at each point. To be able to have this view, it is necessary that the background on which the quantum field is based be conformal invariant as well. Consequently, defining the unambiguous expectation value of the energy-momentum tensor of such a quantum field through the Wald renormalizing prescription necessitates breaking down the conformal symmetry of the background. Then, noticing the field equations suitable for describing the backreaction effect, we show that the existence of the “trace anomaly,” known for indicating the brokenness of conformal symmetry in quantum field theory, can also indicate the above “gravitational” conformal symmetry brokenness.

In this work we show that a relativistic spinning particle can be described at the classical and the quantum level as being composed of two physical constituents which are entangled and separated by a fixed distance. This bilocal model for spinning particles allows for a natural description of particle interactions as a local interaction at each of the constituents. This form of the interaction vertex provides a resolution to a long standing issue on the nature of relativistic interactions for spinning objects in the context of the worldline formalism. It also potentially brings a dynamical explanation for why massive fundamental objects are naturally of lowest spin. We analyze first a nonrelativistic system where spin is modeled as an entangled state of two particles with the entanglement encoded into a set of constraints. It is shown that these constraints can be made relativistic and that the resulting description is isomorphic to the usual description of the phase space of massive relativistic particles with the restriction that the quantum spin has to be an integer.

We report long-term simulations of black hole-neutron star binary mergers where the neutron star possesses an asymmetric magnetic field dipole. Focusing on the scenario where the neutron star is tidally disrupted by the black hole, we track the evolution of the binary up to $\approx 100\mathrm{ms}$ after the merger. We uncover more than one episode of thermally driven winds being launched along a funnel wall in all these cases beginning from $\approx 25\mathrm{ms}$ after the merger. On the other hand, we are unable to conclude presently whether the amount of ejected mass increases with the degree of asymmetry. A large-scale magnetic field configuration in the poloidal direction is formed along the funnel wall accompanied by the generation of a large Poynting flux. The magnetic field in the accretion disk around the black hole remnant is amplified by both magnetic winding and the nonaxisymmetric magnetorotational instability (MRI). The MRI growth is estimated to be in the ideal magnetohydrodynamics (MHD) regime and thus would be free from significant effects induced by potential neutrino radiation. However, the asymmetry in the magnetic field leads to increased turbulence, which causes the vertical magnetic field in the accretion disk to grow largely in a nonlinear manner.

A new model of thermal inflation is introduced, in which the mass of the thermal waterfall field is dependent on a light spectator scalar field. Using the $\delta N$ formalism, the “end of inflation” scenario is investigated in order to ascertain whether this model is able to produce the dominant contribution to the primordial curvature perturbation. A multitude of constraints are considered so as to explore the parameter space, with particular emphasis on key observational signatures. For natural values of the parameters, the model is found to yield a sharp prediction for the scalar spectral index and its running, well within the current observational bounds.

In this paper we constrain some aspects of the general postinflationary phase in the context of superconformal $\alpha$-attractor models of inflation. In particular, we provide constraints on the duration of the reheating process, $N_{\mathrm{reh}}$, and on the reheating temperature, $T_{\mathrm{reh}}$, simulating possible and future results given by the next generation of cosmological missions. Moreover, we stress what kinds of equation-of-state parameter, $w_{\mathrm{reh}}$, are favored for different scenarios. The analysis does not depend on the details of the reheating phase, and it is performed assuming different measurements of the tensor-to-scalar ratio $r$.

Bumblebee models are effective field theories describing a vector field with a nonzero vacuum expectation value that spontaneously breaks Lorentz invariance. They provide an alternative way of exploring the similarities between theories with spontaneous Lorentz symmetry breaking and gauge theories. The equivalence between bumblebee models with suitable conditions and standard electrodynamics in a nonlinear gauge $A_{\mu }{A}^{\mu }+b^2=0$ is taken for granted; however, this point is very subtle and has not yet been fully addressed. The main goal of this paper is to fill in this gap. More precisely, here we study the relation between a bumblebee model, with a smooth potential of the form $V(B_{\mu })=V(B_{\mu }{B}^{\mu }+b^2)$, and standard electrodynamics in the nonlinear gauge $A_{\mu }{A}^{\mu }+b^2=0$, both at the classical and quantum levels. Using Dirac’s method we show that after introducing Dirac brackets with suitable initial conditions, the classical dynamics of the bumblebee model corresponds to that of standard electrodynamics in the aforementioned nonlinear gauge. In the quantum case we demonstrate that perturbative calculations of Feynman amplitudes to any physical process in each model are indistinguishable. To do this, we show that the Feynman rules and propagators of standard electrodynamics in the nonlinear gauge and those describing the bumblebee model are the same.

We discuss analytic continuation as a tool to extract the cumulants of the quark number fluctuations in the strongly interacting medium from lattice QCD simulations at imaginary chemical potentials. The method is applied to $N_f=2+1$ QCD, discretized with stout improved staggered fermions, physical quark masses and the tree level Symanzik gauge action, exploring temperatures ranging from 135 up to 350 MeV and adopting mostly lattices with $N_t=8$ sites in the temporal direction. The method is based on a global fit of various cumulants as a function of the imaginary chemical potentials. We show that it is particularly convenient to consider cumulants up to order two, and that below $T_c$ the method can be advantageous, with respect to a direct Montecarlo sampling at $\mu =0$, for the determination of generalized susceptibilities of order four or higher, and especially for mixed susceptibilities, for which the gain is well above one order of magnitude. We provide cumulants up to order eight, which are then used to discuss the radius of convergence of the Taylor expansion and the possible location of the second-order critical point at real $\mu$: no evidence for such a point is found in the explored range of $T$ and for chemical potentials within present determinations of the pseudocritical line.

The principle of maximal conformality (PMC) provides a rigorous method for eliminating renormalization scheme-and-scale ambiguities for perturbative QCD (pQCD) predictions. The PMC uses the renormalization group equation to fix the $\beta$ pattern of each order in an arbitrary pQCD approximant, and it then determines the optimal renormalization scale by absorbing all $\{{\beta }_i\}$ terms into the running coupling at each order. The resulting coefficients of the pQCD series match the scheme-independent conformal series with $\beta =0$. As in QED, different renormalization scales appear at each order; we call this the multiscale approach. In this paper, we present a novel single-scale approach for the PMC, in which a single effective scale is constructed to eliminate all nonconformal $\beta$ terms up to a given order simultaneously. The PMC single-scale approach inherits the main features of the multiscale approach; for example, its predictions are scheme independent, and the pQCD convergence is greatly improved due to the elimination of divergent renormalon terms. As an application of the single-scale approach, we investigate the $e^{+}{e}^{-}$ annihilation cross-section ratio $R_{e^{+}{e}^{-}}$ and the Higgs decay width $\mathrm{\Gamma }(H\to b\overline{b})$, including four-loop QCD contributions. The resulting predictions are nearly identical to the multiscale predictions for both the total and differential contributions. Thus in many cases, the PMC single-scale approach PMC-s, which requires a simpler analysis, could be adopted as a reliable substitution for the PMC multiscale approach for setting the renormalization scale for high-energy processes, particularly when one does not need detailed information at each order. The elimination of the renormalization scale uncertainty increases the precision of tests of the Standard Model at the LHC.

Using $(223.7\pm 1.4)\times 10^6$ $J/\psi$ events accumulated with the BESIII detector, we study ${\eta }_c$ decays to $\varphi \varphi$ and $\omega \varphi$ final states. The branching fraction of ${\eta }_c\to \varphi \varphi$ is measured to be $\mathrm{Br}({\eta }_c\to \varphi \varphi )=(2.5\pm 0.3_{-0.7}^{+0.3}\pm 0.6)\times {10}^{-3}$, where the first uncertainty is statistical, the second is systematic, and the third is from the uncertainty of $\mathrm{Br}(J/\psi \to \gamma {\eta }_c)$. No significant signal for the double Okubo-Zweig-Iizuka suppressed decay of ${\eta }_c\to \omega \varphi$ is observed, and the upper limit on the branching fraction is determined to be $\mathrm{Br}({\eta }_c\to \omega \varphi )<2.5\times {10}^{-4}$ at the 90% confidence level.

It has been argued that the recently detected ring-down gravity waveforms could be indicative only of the presence of light rings in a horizonless object, such as a surgical Schwarzschild wormhole, with the frequencies differing drastically from those of the horizon quasinormal mode frequencies ${\omega }_{\mathrm{QNM}}$ at late times. While the possibility of such a horizonless alternative is novel by itself, we show by the example of the Ellis-Bronnikov wormhole that the differences in ${\omega }_{\mathrm{QNM}}$ in the eikonal limit (large $l$) need not be drastic. This result will be reached by exploiting the connection between ${\omega }_{\mathrm{QNM}}$ and the Bozza strong field lensing parameters. We shall also show that the lensing observables of the Ellis-Bronnikov wormhole can be very close to those of a black hole (say, $\text{Sgr}{\mathrm{A}}^{*}$ hosted by our galaxy) of the same mass. This situation indicates that the ring-down frequencies and lensing observables of the Ellis-Bronnikov wormhole can remarkably mimic those of a black hole. The constraint on wormhole parameter $\gamma$ imposed by experimental accuracy is briefly discussed. We also provide independent arguments supporting the stability of the Ellis-Bronnikov wormhole proven recently.

In a large class of scalar-tensor theories that are potential candidates for dark energy, a nonminimal coupling between the scalar and the photon is possible. The presence of such an interaction grants us the exciting prospect of directly observing dark sector phenomenology in the electromagnetic spectrum. This paper investigates the behavior of one-electron atoms in this class of modified gravity models, exploring their viability as probes of deviations from general relativity in both laboratory and astrophysical settings. Building heavily on earlier studies, our main contribution is threefold: A thorough analysis finds additional fine-structure corrections previously unaccounted for, which now predict a contribution to the Lamb shift that is larger by nearly 4 orders of magnitude. In addition, they also predict a scalar-mediated photon-photon interaction, which now constrains the scalar’s coupling to the photon independently of the matter coupling. This was not previously possible with atomic precision tests. Our updated constraints are ${\log }_{10}{\beta }_m\lesssim 13.4$ and ${\log }_{10}{\beta }_{\gamma }\lesssim 19.0$ for the matter and photon coupling, respectively, although these remain uncompetitive with bounds from other experiments. Second, we include the effects of the nuclear magnetic moment, allowing for the study of hyperfine structure and the 21 cm line, which hitherto have been unexplored in this context. Finally, we also examine how a background scalar leads to equivalence principle violations.

With the experimental evidences of ${\overline{B}}^0\to p\overline{p}$ and $B^{-}\to \mathrm{\Lambda }\overline{p}$ decays, it is now possible to extract both tree and penguin amplitudes of the charmless two-body baryonic $B$ decays for the first time. The extracted penguin-tree ratio agrees with the expectation. Using the topological amplitude approach with the experimental results on ${\overline{B}}^0\to p\overline{p}$ and $B^{-}\to \mathrm{\Lambda }\overline{p}$ decay rates as input, predictions on all other ${\overline{B}}_q\to \mathcal{B}\overline{\mathcal{B}}$, $\mathcal{B}\overline{\mathcal{D}}$, $\mathcal{D}\overline{\mathcal{B}}$ and $\mathcal{D}\overline{\mathcal{D}}$ decay rates, where $\mathcal{B}$ and $\mathcal{D}$ are the low lying octet and decuplet baryons, respectively, are given. It is nontrivial that the results do not violate any existing experimental upper limit. From the analysis it is understandable that why ${\overline{B}}^0\to p\overline{p}$ and $B^{-}\to \mathrm{\Lambda }\overline{p}$ modes are the first two modes with experimental evidences. Relations on rates are verified using the numerical results. We note that the predicted $B^{-}\to p\overline{{\mathrm{\Delta }}^{++}}$ rate is close to the experimental bound, which has not been updated in the last ten years. Direct $CP$ asymmetries of all ${\overline{B}}_q\to \mathcal{B}\overline{\mathcal{B}}$, $\mathcal{B}\overline{\mathcal{D}}$, $\mathcal{D}\overline{\mathcal{B}}$ and $\mathcal{D}\overline{\mathcal{D}}$ modes are explored. Relations on $CP$ asymmetries are examined using the numerical results. The direct $CP$ asymmetry of ${\overline{B}}^0\to p\overline{p}$ decay can be as large as $\pm 50\%$. Some of the $CP$ asymmetries can serve as tests of the Standard Model. Most of them are pure penguin modes, which are expected to be sensitive to new physics contributions. In particular, ${\overline{B}}_s^0\to {\mathrm{\Xi }}^{-}\overline{{\mathrm{\Xi }}^{-}}$, ${\overline{B}}^0\to {\mathrm{\Xi }}^{-}\overline{{\mathrm{\Sigma }}^{*-}}$, ${\overline{B}}^0\to {\mathrm{\Omega }}^{-}\overline{{\mathrm{\Xi }}^{-}}$, ${\overline{B}}_s^0\to {\mathrm{\Sigma }}^{*-}\overline{{\mathrm{\Sigma }}^{*-}}$, ${\overline{B}}_s^0\to {\mathrm{\Omega }}^{-}\overline{{\mathrm{\Omega }}^{-}}$, ${\overline{B}}_s^0\to {\mathrm{\Xi }}^{-}\overline{{\mathrm{\Xi }}^{*-}}$, ${\overline{B}}_s^0\to {\mathrm{\Xi }}^{*-}\overline{{\mathrm{\Xi }}^{-}}$, ${\overline{B}}^0\to {\mathrm{\Xi }}^{*-}\overline{{\mathrm{\Sigma }}^{*-}}$, ${\overline{B}}^0\to {\mathrm{\Omega }}^{-}\overline{{\mathrm{\Xi }}^{*-}}$ and ${\overline{B}}_s^0\to {\mathrm{\Xi }}^{*-}\overline{{\mathrm{\Xi }}^{*-}}$ decays are $\mathrm{\Delta }S=-1$ pure penguin modes with unsuppressed rates, which can be searched in the near future. Their $CP$ asymmetries are constrained to be of few % and are good candidates to be added to the list of the tests of the Standard Model.

Based on the experimental data released recently by the CLAS Collaboration, the $f_1(1285)$ photoproduction off a proton target is investigated in an effective Lagrangian approach. In our model, $s$-channel, $u$-channel, and $t$-channel Born terms are included to calculate the differential cross sections, which are compared with the recent CLAS experiment. An interpolating Reggeized treatment is applied to the $t$ channel, and it is found that the $t$-channel contribution is dominant in the $f_1(1285)$ photoproduction and the $u$-channel contribution is responsible for the enhancement at backward angles. The present calculation does not take into account any explicit $s$-channel nucleon-resonance contribution; nevertheless, our model provides a good description of the main features of the data. It suggests small couplings of the $f_1(1285)$ and the nucleon resonances in this energy region.

We investigate the deflection of light by a rotating global monopole spacetime and a rotating Letelier spacetime in the weak deflection approximation. To this end, we apply the Gauss-Bonnet theorem to the corresponding osculating optical geometries and show that the deflection of light increases in each spacetime due to the presence of the global monopole parameter and the string cloud parameter, respectively. The results obtained for the deflection angle in the equatorial plane generalize known results for the corresponding nonrotating global monopole and Letelier spacetimes as well as the Kerr solution.

Working within the post-Newtonian (PN) approximation to general relativity, we use the effective field theory (EFT) framework to study the conservative dynamics of the two-body motion at fourth PN order, at fifth order in the Newton constant. This is one of the missing pieces preventing the computation of the full Lagrangian at fourth PN order using EFT methods. We exploit the analogy between diagrams in the EFT gravitational theory and two-point functions in massless gauge theory, to address the calculation of four-loop amplitudes by means of standard multiloop diagrammatic techniques. For those terms which can be directly compared, our result confirms the findings of previous studies, performed using different methods.

The field equations for Einstein-Maxwell-dilaton gravity in $D$ dimensions are reduced to an effective one-dimensional system under the influence of exponential potentials. Various cases where exact solutions can be found are explored. With this procedure, we present interesting solutions such as a one-parameter generalization of the dilaton-Melvin spacetime and a three-parameter solution that interpolates between the Reissner-Nordström and Bertotti-Robinson solutions. This procedure also allows simple, alternative derivations of known solutions such as the Lifshitz spacetime and the planar anti–de Sitter naked singularity. In the latter case, the metric is cast in a simpler form which reveals the presence of an additional curvature singularity.