The STAR Collaboration reports measurements of the longitudinal double-spin asymmetry, $A_{LL}$, for neutral pions produced at forward directions in polarized proton-proton collisions, at a center-of-mass energy of 510 GeV. Results are given for transverse momenta in the range $2<p_T<10\mathrm{GeV}/c$ within two regions of pseudorapidity that span $2.65<\eta <3.9$. These results are sensitive to the polarized gluon parton distribution function, $\mathrm{\Delta }g(x)$, down to the region of Bjorken $x\sim {10}^{-3}$. The asymmetries observed are less than $\pm 5\times {10}^{-3}$ in magnitude and will help constrain the contribution to the spin of the proton from polarized gluons at low $x$, when combined with other measurements as part of a global analysis.

In [1] it was shown that the four-dimensional Einstein-dilaton-Gauss-Bonnet theory allows for wormholes without introducing any exotic matter. The numerical solution for the wormhole was obtained there and it was claimed that this solution is gravitationally stable against radial perturbations, what, by now, would mean the only known theoretical possibility for the existence of an apparently stable, four-dimensional and asymptotically flat wormhole without exotic matter. Here, more detailed analysis of perturbations shows that the Kanti-Kleihaus-Kunz wormhole is unstable against small perturbations for any values of its parameters. The exponential growth appears in the time domain after a long period of damped oscillations, in the same way as it takes place in the case of unstable higher-dimensional black holes in the Einstein-Gauss-Bonnet theory. The instability is driven by the purely imaginary mode, which is nonperturbative in the Gauss-Bonnet coupling $\alpha$.

In this paper we on inflationary dynamics in the context of Einstein-Gauss-Bonnet gravitational theories. We investigate the implications of the slow-roll condition on the slow-roll indices and we investigate how the inflationary dynamical evolution is affected by the presence of the Gauss-Bonnet coupling to the scalar field. To exemplify our analysis, we investigate how the dynamics of inflationary cubic-order, quartic-order, and exponential scalar potentials are affected by the nontrivial Gauss-Bonnet coupling to the scalar field. As we demonstrate, it is possible to obtain a viable phenomenology compatible with the observational data, although the canonical scalar field theory with cubic- and quartic-order potentials does not yield phenomenologically acceptable results. In addition, with regard to the exponential potential example, the Einstein-Gauss-Bonnet extension of the single canonical scalar field model has an inherent mechanism that can trigger the graceful exit from inflation. Furthermore, we introduce a bottom-up reconstruction technique where, by fixing the tensor-to-scalar ratio and the Hubble rate as a function of the $e$-folding number, one is capable of reproducing the Einstein-Gauss-Bonnet theory which generates the aforementioned quantities. We illustrate how the method works by using some relatively simple examples.

We study scalar-tensor theories respecting the projective invariance in the metric-affine formalism. The metric-affine formalism is a formulation of gravitational theories such that the metric and the connection are independent variables in the first place. In this formalism, the Einstein-Hilbert action has an additional invariance, called the projective invariance, under a shift of the connection. Respecting this invariance for the construction of the scalar-tensor theories, we find that the Galileon terms in curved spacetime are uniquely specified at least up to quartic order which does not coincide with either the covariant Galileon or the covariantized Galileon. We also find an action in the metric-affine formalism which is equivalent to class ${}^2\mathrm{N}\text{−}\mathrm{I}/\mathrm{Ia}$ of the quadratic degenerated higher order scalar-tensor (DHOST) theory. The structure of DHOST would become clear in the metric-affine formalism since the equivalent action is just linear in the generalized Galileon terms and non-minimal couplings to the Ricci scalar and the Einstein tensor with independent coefficients. The fine-tuned structure of DHOST is obtained by integrating out the connection. In these theories, nonminimal couplings between fermionic fields and the scalar field may be predicted. We discuss possible extensions which could involve theories beyond DHOST.

We study gravitational wave production during Abelian gauge-field preheating following inflation. We consider both scalar and pseudoscalar inflaton models coupled directly to Abelian gauge fields via either a dilatonic coupling to the gauge-field kinetic term or an axial coupling to a Chern-Simons term. In both cases gravitational waves are produced efficiently during the preheating phase, with a signature louder than most cosmological signals. These gravitational waves can contribute to the radiation energy budget of Universe at a level which will be probed by upcoming cosmic microwave background experiments through $N_{\mathrm{eff}}$. For axially coupled fields the resulting gravitational wave spectrum is helically polarized—a unique feature that can be used to differentiate it from other stochastic gravitational wave backgrounds. We compute the gravitational topological charge and demonstrate that gauge preheating following axion inflation may be responsible for the matter-antimatter asymmetry of the Universe via gravitational leptogenesis.

The observations of a macronova/kilonova accompanied by gravitational waves from a binary neutron star merger (GW170817) confirmed that neutron star coalescences produce copious ejecta. The coincident gamma-ray detection implies the existence of a relativistic jet in this system. During the jet’s propagation within the ejecta, high-energy photons and neutrinos can be produced. The photons are absorbed by the ejecta, while the neutrinos escape and can be detected. Here, we estimate such transejecta neutrino emission, and discuss how neutrino observations could be used to differentiate between gamma-ray burst emission scenarios. We find that neutrinos from the internal shocks inside the ejecta may be detectable by IceCube within a few years of operation, and will likely be detected with IceCube-Gen2. The neutrino signals coincident with gravitational waves would enable us to reveal the physical quantities of the choked jets even without electromagnetic signals.

The ANITA experiment has observed two unusual upgoing air shower events, which are consistent with the $\tau$-lepton decay origin. However, these events are in contradiction with the standard neutrino-matter interaction models as well as the EeV diffuse neutrino flux limits set by IceCube and the cosmic ray facilities like AUGER. In this paper, we have reinvestigated the possibility of using the sterile neutrino hypothesis to explain the ANITA anomalous events. The diffuse flux of the sterile neutrinos is less constrained by the IceCube and AUGER experiments due to the small active-sterile mixing angle suppression. The quantum decoherence effect should be included for describing the neutrino flux propagating in the Earth matter, because the interactions between neutrinos and the Earth matter are very strong at the EeV energy scale. After several experimental approximations, we show that the ANITA anomaly itself is able to be explained by the sterile neutrino origin, but we also predict that the IceCube observatory should have more events than ANITA. It makes the sterile neutrino origin very unlikely to account for both of them simultaneously. A more solid conclusion can be drawn by the dedicated ANITA signal simulation.

We study perturbative unitarity in the scalar sector of the Myers-Pospelov model. The model introduces a preferred four-vector $n$ which breaks Lorentz symmetry and couples to a five-dimension operator. When the preferred four-vector is chosen in the pure timelike or lightlike direction, the model becomes a higher time derivative theory, leading to a cubic dispersion relation. Two of the poles are shown to be perturbatively connected to the standard ones, while a third pole, which we call the Lee-Wick-like pole, is associated to a negative metric in Hilbert space, threatening the preservation of unitarity. The pure spacelike case is a normal theory in the sense that it has only two solutions, both being small perturbations over the standard ones. We analyze perturbative unitarity for purely spacelike and timelike cases using the optical theorem and considering a quartic self-interaction term. By computing discontinuities in the loop diagram, we arrive at a pinching condition which determines the propagation of particles and Lee-Wick-like particles through the cut. We find that the contribution for Lee-Wick-like particles vanishes for any external momenta, leaving only the contribution of particles, thus preserving one-loop unitarity in both cases.

We study the gauge dependence of the neutrino mass renormalization in a two Higgs doublet model, that is extended with one singlet seesaw neutrino. This model gives only one light neutrino a mass at tree level, while the second light mass is generated at loop level via the interaction with the second Higgs doublet. At one loop level, one neutrino stays massless. We use multiplicative renormalization constants to define counterterms. The renormalized mass parameters are defined as the complex poles of the propagators, using the complex mass scheme for mass renormalization. With this setup, we analytically get the expressions for the neutrino mass counterterms and isolate the gauge dependent part. We show, how relating this gauge dependent part with the tadpole renormalization leads to gauge independent counterterm definitions, hence gauge independent bare masses for neutrinos.

The recent observation and measurement of the decay $Z_c(3900)\to \rho {\eta }_c$ provides the data on the relative strength of the pion and $\rho$ coupling in the corresponding transitions between exotic resonances and pure heavy quarkonium. It is argued that using these data, the heavy quark limit for the $c$ and $b$ quarks, the heavy quark spin symmetry (HQSS) and the vector dominance for photon emission by the light quarks, one can (approximately) quantitatively estimate the rates of the radiative transitions from $\mathrm{\Upsilon }(5S)$ to the expected $G$-odd states of molecular bottomonium $W_{bJ}$. The estimate of the cross section of the processes $e^{+}{e}^{-}\to \gamma W_{bJ}$ at the maximum of the $\mathrm{\Upsilon }(5S)$ resonance comes out in the ballpark of 0.1 pb, which sets a benchmark for a possible search for these processes at BelleII.

We present calculations of radiative transitions between vector and pseudoscalar quarkonia in the light-front Hamiltonian approach. The valence sector light-front wave functions of heavy quarkonia are obtained from the Basis Light-Front Quantization approach in a holographic basis. We study the transition form factor with both the traditional “good current” $J^{+}$ and the transverse current ${\overrightarrow{J}}_{\perp }$ (in particular, $J^R=J^x+i{J}^y$). This allows us to investigate the role of rotational symmetry by considering vector mesons with different magnetic projections ($m_j=0,\pm 1$). We use the $m_j=0$ state of the vector meson to obtain the transition form factor, since this procedure employs the dominant spin components of the light-front wave functions and is more robust in practical calculations. While the $m_j=\pm 1$ states are also examined, transition form factors depend on subdominant components of the light-front wave functions and are less robust. Transitions between states below the open-flavor thresholds are computed, including those for excited states. Comparisons are made with the experimental measurements, as well as with lattice QCD and quark model results. In addition, we apply the transverse current to calculate the decay constant of vector mesons where we obtain consistent results using either $m_j=0$ or $m_j=1$ light-front wave functions. This consistency provides evidence for features of rotational symmetry within the model.

The effect of the second class currents with and without time reversal invariance has been studied in the quasielastic production of nucleons and hyperons induced by neutrinos and antineutrinos from the nucleons. The numerical results are presented for the total scattering cross section ($\sigma$) as well as for the longitudinal, perpendicular, and transverse components of the polarization of the final baryons ($p$, $n$, $\mathrm{\Lambda }$, ${\mathrm{\Sigma }}^{-}$, ${\mathrm{\Sigma }}^0$) and muon produced in the quasielastic (anti)neutrino-nucleon scattering induced by the weak charged current. In the case of the production of the $\mathrm{\Lambda }$ hyperon, which is the most suitable candidate for making the polarization measurements, we have also calculated the $Q^2$ dependence of the polarization observables and the differential scattering cross section ($d\sigma /d{Q}^2$). The measurement of the polarization observables and their $Q^2$ dependence provides an independent way to determine the nucleon-hyperon transition form factors at high $Q^2$ which can provide tests of the symmetries of the weak hadronic currents like G invariance, T invariance, and SU(3) symmetry.

The $CP$ nature of the Higgs coupling to top quarks is addressed in this paper, in single charged lepton final states of $t\overline{t}h$ events produced in proton-proton collisions at the LHC. Pure scalar ($h=H$) and pseudoscalar ($h=A$) Higgs boson signal events, generated with MadGraph5_aMC@NLO, are fully reconstructed using a kinematic fit. Angular distributions of the decay products, as well as $CP$-sensitive asymmetries, are exploited to separate and gain sensitivity to possible pseudoscalar components of the Higgs boson and reduce the contribution from the dominant irreducible background $t\overline{t}b\overline{b}$. Significant differences are found between the pure $CP$-even and -odd signal hypotheses as well as with respect to the Standard Model background, in particular the $t\overline{t}b\overline{b}$ contribution. Such differences survive the event reconstruction, allowing one to define optimal observables to extract the Higgs couplings parameters from a global fit. A dedicated analysis is applied to efficiently identify signal events and reject as much as possible the expected Standard Model background. The results obtained are compared with a similar analysis in the dilepton channel. We show that the single lepton channel is more promising overall and can be used in combination to study the $CP$ nature of the Higgs coupling to top quarks.

We study the one-loop gluon polarization tensor at zero and finite temperature in the presence of a magnetic field, to extract the thermomagnetic evolution of the strong coupling ${\alpha }_s$. We analyze four distinct regimes, to wit, the small and large field cases, both at zero and at high temperature. From a renormalization group analysis, we show that at zero temperature, either for small or large magnetic fields, and for a fixed transferred momentum $Q^2$, ${\alpha }_s$ grows with the field strength with respect to its vacuum value. However, at high temperature and also for a fixed value of $Q^2$, we find two different cases. When the magnetic field is even larger than the squared temperature, ${\alpha }_s$ also grows with the field strength. On the contrary, when the squared temperature is larger than the magnetic field, a turnover behavior occurs, and ${\alpha }_s$ decreases with the field strength. This thermomagnetic behavior of ${\alpha }_s$ can help explain the inverse magnetic catalysis phenomenon found by lattice QCD calculations.

The Eisenhart lift of a Paul trap used to store ions in molecular physics is a linearly polarized periodic gravitational wave. A modified version of Dehmelt’s Penning trap is, in turn, related to circularly polarized periodic gravitational waves, sought in inflationary models. Similar equations also govern the Lagrange points in celestial mechanics. The explanation is provided by anisotropic oscillators.

We compute the rotations, during a scattering encounter, of the spins of two gravitationally interacting particles at second order in the gravitational constant (second post-Minkowskian order). Following a strategy introduced by us [D. Bini and T. Damour, Phys. Rev. D 96, 104038 (2017)], we transcribe our result into a correspondingly improved knowledge of the spin-orbit sector of the effective one-body (EOB) Hamiltonian description of the dynamics of spinning binary systems. We indicate ways of resumming our results for defining improved versions of spinning EOB codes which might help in providing a better analytical description of the dynamics of coalescing spinning binary black holes.

The existence of axionlike particles (ALPs) is predicted by many extensions of the standard model of elementary particles and in particular by theories of superstrings and superbranes. ALPs are very light, neutral, pseudoscalar bosons which are supposed to interact with two photons. They can play an important role in high-energy astrophysics. Basically, in certain circumstances, ALPs substantially enhance the photon survival probability $P_{\gamma \to \gamma }(\mathcal{E})$ of a beam emitted by a far-away source through the mechanism of photon-ALP oscillations ($\mathcal{E}$ denotes the energy). But in order for this to work, an external magnetic field $\mathbf{B}$ must be present. In several cases, $\mathbf{B}$ is modeled as a domainlike network with “sharp edges”: all domains have the same size $L_{\mathrm{dom}}$ (set by the $\mathbf{B}$ coherence length) and the same strength $B$, but the direction of $\mathbf{B}$ changes randomly and abruptly from one domain to the next. While this model has repeatedly been used since it greatly simplifies the calculations, it is obviously a highly mathematical idealization wherein the components of $\mathbf{B}$ are discontinuous across the edges (whence the name sharp edges). It is therefore highly desirable to go a step further and to find out what happens when the edges are smoothed out, namely when the abrupt change of $\mathbf{B}$ is replaced by a smooth one. Moreover, this step becomes compelling when the photon-ALP oscillation length $l_{\mathrm{osc}}$ turns out to be comparable to—or smaller than—$L_{\mathrm{dom}}$, because in this case, the photon survival probability $P_{\gamma \to \gamma }(\mathcal{E})$ critically depends on the domain shape. Finally, it would be more realistic to have $L_{\mathrm{dom}}$ randomly changing within a given range, since it looks rather unlikely that the coherence length of $\mathbf{B}$ should be the same everywhere, especially when its source is sufficiently extended. In the present paper, we propose a smoothed out version of the previous domainlike structure of $\mathbf{B}$ which incorporates the above changes, and we work out its implications. Even in the present case, we are able to solve analytically and exactly the propagation equation of a monochromatic photon/ALP beam of energy $\mathcal{E}$ inside a single smoothed out domain, thereby ultimately evaluating the corresponding photon survival probability $P_{\gamma \to \gamma }(\mathcal{E})$ exactly. This fact has the great advantage to drastically shorten the computation time in the applications involving computer simulations as compared to a numerical solution of the beam propagation equation. Actually, it turns out that the condition $l_{\mathrm{osc}}\lesssim L_{\mathrm{dom}}$ takes place when a photon/ALP beam of either very low $\mathcal{E}$ or very large $\mathcal{E}$—both in the gamma-ray band—crosses a variety of astronomical objects, like radio lobes of flat spectrum radio quasars, spiral galaxies, starburst galaxies, elliptical galaxies, and extragalactic space. Thus, the use of our model becomes compelling in all these instances, since the sharp edges model would yield unphysical results. The case of extragalactic space is of particular importance in view of the new generation of gamma-ray observatories like CTA, HAWC, GAMMA-400, LHAASO, and TAIGA-HiSCORE, since in such a situation $l_{\mathrm{osc}}\lesssim L_{\mathrm{dom}}$ occurs for $\mathcal{E}\gtrsim \mathcal{O}(40\mathrm{TeV})$ with a large uncertainty, depending on the choice of the model parameters (we shall come back to this fundamental issue in a subsequent paper).

Form factors of the rare ${\mathrm{\Lambda }}_b({\mathrm{\Lambda }}_b^{*})\to N{\ell }^{+}{\ell }^{-}$ decays are calculated in the framework of the light cone QCD sum rules by taking into account the contributions from the negative parity baryons. Using the obtained results on the form factors, the branching ratios of the considered decays are estimated. The numerical survey for the branching ratios of the ${\mathrm{\Lambda }}_b\to N{\ell }^{+}{\ell }^{-}$ and ${\mathrm{\Lambda }}_b^{*}\to N{\ell }^{+}{\ell }^{-}$ decays indicate that these transitions could be measurable in LHCb in near future. Comparison of our predictions on the form factors and branching ratios with those existing in the literature is also performed.

We investigate a simple realistic grand unified theory based on the $SU(5)$ gauge symmetry, which predicts an upper bound on the proton decay lifetime for the channels $p\to K^{+}\overline{\nu }$ and $p\to {\pi }^{+}\overline{\nu }$, i.e., $\tau (p\to K^{+}\overline{\nu })\lesssim 3.4\times {10}^{35}$ and $\tau (p\to {\pi }^{+}\overline{\nu })\lesssim 1.7\times {10}^{34}\mathrm{years}$, respectively. In this context, the neutrino masses are generated through the type I and type III seesaw mechanisms, and one predicts that the field responsible for type III seesaw must be light with a mass below 500 TeV. We discuss the testability of this theory at current and future proton decay experiments.