We consider exclusive multiperipheral production of four charged pions in proton-proton collisions at high energies with simultaneous exchange of three Pomerons/Reggeons. The amplitude(s) for the genuine $2\to 6$ process are written in the Regge approach. The calculation is performed with the help of the GenEx Monte Carlo code. Some corrections at low invariant masses in the two-body subsystems are necessary for application of the Regge formalism. We estimate the corresponding cross section and present differential distributions in rapidity, transverse momenta and two- and four-pion invariant masses. The cross section and the distributions depend on the value of the cutoff parameter of a form factor correcting amplitudes for off-shellness of $t$-channel pions. A rather large cross section is found for the whole phase space ($\sigma \sim 1–5\mu \mathrm{b}$, including absorption corrections). Relatively large four-pion invariant masses are populated in the considered diffractive mechanism compared to other mechanisms discussed so far in the context of four-pion production. We investigate whether the triple Regge exchange processes could be identified with the existing LHC detectors. We consider the case of ATLAS and ALICE cuts. The ATLAS (or CMS) has a better chance to identify the process in the region of large invariant masses $M_{4\pi }>10\mathrm{GeV}$. In the case of the ALICE experiment the considered mechanism competes with other mechanisms (production of $\sigma \sigma$, $\rho \rho$ pairs or single resonances) and cannot be unambiguously identified.

We revisit the global QCD analysis of parton-to-kaon fragmentation functions at next-to-leading-order accuracy using the latest experimental information on single-inclusive kaon production in electron-positron annihilation, lepton-nucleon deep-inelastic scattering, and proton-proton collisions. An excellent description of all data sets is achieved, and the remaining uncertainties in parton-to-kaon fragmentation functions are estimated and discussed based on the Hessian method. Extensive comparisons to the results from our previous global analysis are made.

We continue our study on the capabilities of present and future x-ray missions to test the nature of astrophysical black hole candidates via x-ray reflection spectroscopy and distinguish Kerr black holes from other solutions of 4-dimensional Einstein’s gravity in the presence of a matter field. Here we investigate the case of Kerr black holes with Proca hair [1]. The analysis of a sample of these configurations suggests that even extremely hairy black holes can mimic the iron line profile of the standard Kerr black holes, and, at least for the configurations of our study, we find that current x-ray missions cannot distinguish these objects from Kerr black holes. This contrasts with our previous findings for the case of Kerr black holes with scalar (rather than Proca) hair [2], even though such comparison may be biased by the limited sample. Future x-ray missions can detect the presence of Proca hair, but a theoretical knowledge of the expected intensity profile (currently missing) can be crucial to obtain strong constraints.

We point out that there are only three polarizations for gravitational waves in $f(R)$ gravity, and the polarization due to the massive scalar mode is a mix of the pure longitudinal and transverse breathing polarization. The classification of the six polarizations by the Newman-Penrose quantities is based on weak, plane and null gravitational waves, so it is not applicable to the massive mode.

Possible spin-parity quantum numbers for excited charmed baryon resonances are discussed in this work. Our main results are as follows. (i) Among the five newly observed ${\mathrm{\Omega }}_c$ states, we have identified ${\mathrm{\Omega }}_c(3090)$ and ${\mathrm{\Omega }}_c(3119)$ with radially excited ${\frac{1}{2}}^{+}(2S)$ and ${\frac{3}{2}}^{+}(2S)$ states, respectively, and ${\mathrm{\Omega }}_c(3000)$ with ${\frac{1}{2}}^{-}(1P)$. The two states ${\mathrm{\Omega }}_c(3050)$ and ${\mathrm{\Omega }}_c(3066)$ form a $P$-wave $({\frac{3}{2}}^{-},{\frac{5}{2}}^{-})$ doublet. (ii) The widths of ${\mathrm{\Omega }}_c(3066)$ and ${\mathrm{\Xi }}_c^{\prime }(2930)$ are calculable within the framework of heavy hadron chiral perturbation theory. (iii) Since the width of ${\mathrm{\Omega }}_{c0}({\frac{1}{2}}^{-})$ is of order 410 MeV, not all observed narrow ${\mathrm{\Omega }}_c$ baryons can be identified with $1P$ states. (iv) For the antitriplet ${\mathrm{\Lambda }}_c$ and ${\mathrm{\Xi }}_c$ states, their Regge trajectories for the orbital excitations of ${\frac{1}{2}}^{-}$ and ${\frac{3}{2}}^{-}$ are parallel to each other. Based on this nice property of parallelism, we see that the highest state ${\mathrm{\Lambda }}_c(2940)$ does not fit if its quantum numbers are ${\frac{3}{2}}^{-}$ as found by LHCb. We suggest that ${\mathrm{\Lambda }}_c(2940{)}^{+}$ is most likely the ${\frac{1}{2}}^{-}(2P)$ state. (v) The charmed baryon ${\mathrm{\Sigma }}_c(2800)$ cannot be a ${\frac{1}{2}}^{-}$ state; otherwise, its width will be over 400 MeV, too large compared to the measured one. (vi) In the study of Regge trajectories of ${\mathrm{\Xi }}_c^{\prime }$ states, we find a missing state. It should have quantum numbers ${\frac{5}{2}}^{-}$ with a mass around 2920 MeV. (vii) Antitriplet and sextet states are classified according to their $J^P(nL)$ quantum numbers. The mass differences between ${\mathrm{\Xi }}_c$ and ${\mathrm{\Lambda }}_c$ in the antitriplet states clearly lie between 180 and 200 MeV. Moreover, the mass splitting between ${\mathrm{\Omega }}_c$ and ${\mathrm{\Xi }}_c^{\prime }$ is found to be very close to the one between ${\mathrm{\Xi }}_c^{\prime }$ and ${\mathrm{\Sigma }}_c$ for five different sets of sextet multiplets. This lends a strong support to the quantum number assignment to the sextet states in this work.

The nucleon spin-averaged forward virtual Compton tensor determines important physical quantities such as electromagnetically induced mass differences of nucleons and two-photon exchange contributions in hydrogen spectroscopy. It depends on two kinematic variables: $\nu$, the virtual photon energy in the proton rest frame, and $Q^2$, the photon’s invariant four-momentum squared. Using the operator product expansion, we calculate the tensor’s large-$Q^2$ behavior for $\nu =0$, including for the first time the full spin-2 contribution and correcting a previous result in the literature for the spin-0 contribution. Implications for the proton radius puzzle are discussed.

We present a new method for calculation of the gravitational self-force (GSF) in Kerr geometry, based on a time-domain reconstruction of the metric perturbation from curvature scalars. In this approach, the GSF is computed directly from a certain scalarlike self-potential that satisfies the time-domain Teukolsky equation on the Kerr background. The approach is computationally much cheaper than existing time-domain methods, which rely on a direct integration of the linearized Einstein’s equations and are impaired by mode instabilities. At the same time, it retains the utility and flexibility of a time-domain treatment, allowing calculations for any type of orbit (including highly eccentric or unbound ones) and the possibility of self-consistently evolving the orbit under the effect of the GSF. Here we formulate our method, and present a first numerical application, for circular geodesic orbits in Schwarzschild geometry. We discuss further applications.

In this work, we compute the corrections in Newton’s law of gravitation due to Kaluza-Klein gravitons in codimension-1 warped thick braneworld scenarios. We focus in some models recently proposed in the literature, the so-called asymmetric hybrid brane and compact brane. Such models are deformations of the ${\varphi }^4$ and sine-Gordon topological defects, respectively. Therefore we consider the branes engendered by such defects and we also compute the corrections in their cases. We use suitable numerical techniques to attain the mass spectrum and its corresponding eigenfunctions which are the essential quantities for computing the correction to the Newtonian potential. Moreover, we discuss that the existence of massive modes is necessary for building a braneworld model with a phenomenology involved. We find that the odd eigenfunctions have nontrivial contributions and the first eigenstate of the Kaluza-Klein tower has the highest contribution. The calculation of slight deviations in the gravitational potential may be used as a selection tool for braneworld scenarios matching with future experimental measurements in high energy collisions.

We present a new method for delensing $B$ modes of the cosmic microwave background (CMB) using a lensing potential reconstructed from the same realization of the CMB polarization (CMB internal delensing). The $B$-mode delensing is required to improve sensitivity to primary $B$ modes generated by, e.g., the inflationary gravitational waves, axionlike particles, modified gravity, primordial magnetic fields, and topological defects such as cosmic strings. However, the CMB internal delensing suffers from substantial biases due to correlations between observed CMB maps to be delensed and that used for reconstructing a lensing potential. Since the bias depends on realizations, we construct a realization-dependent (RD) estimator for correcting these biases by deriving a general optimal estimator for higher-order correlations. The RD method is less sensitive to simulation uncertainties. Compared to the previous $\ell$-splitting method, we find that the RD method corrects the biases without substantial degradation of the delensing efficiency.

The Raychaudhuri equation for null rays is a powerful tool for finding consistent embeddings of cosmological bubbles in a background spacetime in a way that is largely independent of the matter content. We find that spatially flat or positively curved thin wall bubbles surrounded by a cosmological background must have a Hubble expansion that is either contracting or expanding slower than the background, which is a more stringent constraint than those obtained by the usual Israel thin-wall formalism. Similarly, a cosmological bubble surrounded by Schwarzschild space, occasionally used as a simple “swiss cheese” model of inhomogenities in an expanding universe, must be contracting (for spatially flat and positively curved bubbles) and bounded in size by the apparent horizon.

We present a method to delens the acoustic peaks of the cosmic microwave background (CMB) temperature and polarization power spectra internally, using lensing maps reconstructed from the CMB itself. We find that when delensing CMB acoustic peaks with a lensing potential map derived from the same CMB sky, a large bias arises in the delensed power spectrum. The cause of this bias is that the noise in the reconstructed potential map is derived from, and hence correlated with, the CMB map when delensing. This bias is more significant relative to the signal than an analogous bias found when delensing CMB $B$ modes. We calculate the leading term of this bias, which is present even in the absence of lensing. We also demonstrate one method to remove this bias, using reconstructions from CMB angular scales within given ranges to delens CMB scales outside of those ranges. Some details relevant for a realistic analysis are also discussed, such as the importance of removing mask-induced effects for successful delensing, and a useful null test, obtained from randomizing the phases of the reconstructed potential. Our findings should help current and next-generation CMB experiments obtain tighter parameter constraints via the internal removal of lensing-induced smoothing from temperature and $E$-mode acoustic peaks.

We study the constraints on neutralino dark matter in minimal low energy supersymmetry models and the case of heavy lepton and quark scalar superpartners. For values of the Higgsino and gaugino mass parameters of the order of the weak scale, direct detection experiments are already putting strong bounds on models in which the dominant interactions between the dark matter candidates and nuclei are governed by Higgs boson exchange processes, particularly for positive values of the Higgsino mass parameter $\mu$. For negative values of $\mu$, there can be destructive interference between the amplitudes associated with the exchange of the standard $CP$-even Higgs boson and the exchange of the nonstandard one. This leads to specific regions of parameter space which are consistent with the current experimental constraints and a thermal origin of the observed relic density. In this article, we study the current experimental constraints on these scenarios, as well as the future experimental probes, using a combination of direct and indirect dark matter detection and heavy Higgs and electroweakino searches at hadron colliders.

It has been established that matrix product states can be used to compute the ground state and single-particle excitations and their properties of lattice gauge theories at the continuum limit. However, by construction, in this formalism the Hilbert space of the gauge fields is truncated to a finite number of irreducible representations of the gauge group. We investigate quantitatively the influence of the truncation of the infinite number of representations in the Schwinger model, one-flavor ${\mathrm{QED}}_2$, with a uniform electric background field. We compute the two-site reduced density matrix of the ground state and the weight of each of the representations. We find that this weight decays exponentially with the quadratic Casimir invariant of the representation which justifies the approach of truncating the Hilbert space of the gauge fields. Finally, we compute the single-particle spectrum of the model as a function of the electric background field.

To better understand the nature and internal structure of the exotic states discovered by many collaborations, more information on their electromagnetic properties and their strong and weak interactions with other hadrons is needed. The residue or current coupling constant of these states together with their mass are the main inputs in determinations of such properties. We perform QCD sum rules analyses on the hidden-charm pentaquark states with spin parities $J^P={\frac{3}{2}}^{\pm }$ and $J^P={\frac{5}{2}}^{\pm }$ to calculate their residue and mass. In the calculations, we adopt a molecular picture for $J^P={\frac{3}{2}}^{\pm }$ states and a mixed current in a molecular form for $J^P={\frac{5}{2}}^{\pm }$. Our analyses show that the $P_c^{+}(4380)$ and $P_c^{+}(4450)$, observed by the LHCb Collaboration, can be considered as hidden-charm pentaquark states with $J^P={\frac{3}{2}}^{-}$ and $J^P={\frac{5}{2}}^{+}$, respectively.

Utilizing the holographic technique, we investigate how the entanglement entropy evolves along the renormalization group flow. After introducing a new generalized temperature which satisfies the thermodynamicslike law even in the IR regime, we find that the renormalized entropy and the generalized temperature in the IR limit approach the thermal entropy and thermodynamic temperature of a real thermal system. This result implies that the microscopic quantum entanglement entropy in the IR region leads to the thermodynamic relation up to small quantum corrections caused by the quantum entanglement near the entangling surface. Intriguingly, this IR feature of the entanglement entropy universally happens regardless of the detail of the dual field theory and the shape of the entangling surface. We check this IR universality with a most general geometry called the hyperscaling violation geometry which is dual to a relativistic nonconformal field theory.

The simplicity constraint is studied in the context of four-dimensional spinfoam models with a cosmological constant. We find that the quantum simplicity constraint is realized as the two-dimensional surface defect in $\mathrm{SL}(2,\mathbb{C})$ Chern-Simons theory in the construction of spinfoam amplitudes. By this realization of the simplicity constraint in Chern-Simons theory, we are able to construct the new spinfoam amplitude with a cosmological constant for an arbitrary simplicial complex (with many 4-simplices). The semiclassical asymptotics of the amplitude is shown to correctly reproduce the four-dimensional Einstein-Regge action with a cosmological constant term.

It is known that the Cardassian universe is successful in describing the accelerated expansion of the universe, but its dynamic equations are hard to get from the action principle. In this paper, we establish the connection between the Cardassian universe and $f(T,\mathcal{T})$ gravity, where $T$ is the torsion scalar and $\mathcal{T}$ is the trace of the matter energy-momentum tensor. For dust matter, we find that the modified Friedmann equations from $f(T,\mathcal{T})$ gravity can correspond to those of Cardassian models, and thus, a possible origin of Cardassian universe is given. We obtain the original Cardassian model, the modified polytropic Cardassian model, and the exponential Cardassian model from the Lagrangians of $f(T,\mathcal{T})$ theory. Furthermore, by adding an additional term to the corresponding Lagrangians, we give three generalized Cardassian models from $f(T,\mathcal{T})$ theory. Using the observation data of type Ia supernovae, cosmic microwave background radiation, and baryon acoustic oscillations, we get the fitting results of the cosmological parameters and give constraints of model parameters for all of these models.

Within the framework of general relativity, we investigate the tidal acceleration of astrophysical jets relative to the central collapsed configuration (“Kerr source”). To simplify matters, we neglect electromagnetic forces throughout; however, these must be included in a complete analysis. The rest frame of the Kerr source is locally defined via the set of hypothetical static observers in the spacetime exterior to the source. Relative to such a fiducial observer fixed on the rotation axis of the Kerr source, jet particles are tidally accelerated to almost the speed of light if their outflow speed is above a certain threshold, given roughly by one-half of the Newtonian escape velocity at the location of the reference observer; otherwise, the particles reach a certain height, reverse direction and fall back toward the gravitational source.