We investigate the possibility to study the charmoniumlike state $Z_c(3900)$ through the pion-induced production off a nuclear target. By using a high-energy pion beam, the $Z_c(3900)$ can be produced off a proton or nucleus though the Primakoff effect. The production amplitude is calculated in an effective Lagrangian approach combined with the vector dominance model. The total cross sections of the $p({\pi }^{-},Z_c^{-}(3900))$ and $p({\pi }^{-},Z_c^{-}(3900)\to J/\psi {\pi }^{-})$ reactions are calculated, and their order of magnitude is about 0.1 and 0.01 nb, respectively, with an assumption of branch ratio 10% for the $Z_c(3900)$ decay in $J/\psi \pi$ channel. If the proton target is replaced by a nuclear target, the production of the $Z_c(3900)$ enhances obviously. The predicted total cross sections for the $A({\pi }^{-},Z_c^{-}(3900))$ and $A({\pi }^{-},Z_c^{-}(3900)\to J/\psi {\pi }^{-})$ reactions with $A={}^{12}\mathrm{C}$ or ${}^{208}\mathrm{Pb}$ are on the order of magnitude of 100 and 10 nb, respectively, which is about one thousand times larger than the cross sections off a proton target. Based on these results, we suggest the experimental study of the $Z_c(3900)$ by using high-energy pion beams with a nuclear target at facilities such as COMPASS and J-PARC.

In the case of three quark flavors, (pseudo)scalar diquarks transform as antiquarks under chiral transformations. We construct four spin-$1/2$ baryonic multiplets from left- and right-handed quarks as well as left- and right-handed diquarks. The fact that two of these multiplets transform in a “mirror” way allows for chirally invariant mass terms. We then embed these baryonic multiplets into the Lagrangian of the so-called extended linear sigma model, which features (pseudo)scalar and (axial-)vector mesons, as well as glueballs. Reducing the Lagrangian to the two-flavor case, we obtain four doublets of nucleonic states. These mix to produce four experimentally observed states with definite parity: the positive-parity nucleon $N(939)$ and Roper resonance $N(1440)$, as well as the negative-parity resonances $N(1535)$ and $N(1650)$. We determine the parameters of the nucleonic part of the Lagrangian from a fit to masses and decay properties of the aforementioned states. Studying the limit of vanishing quark condensate, we conclude that $N(939)$ and $N(1535)$, as well as $N(1440)$ and $N(1650)$, form pairs of chiral partners.

The decay ${\mathrm{\Xi }}_b^{-}\to {\pi }^{-}{\mathrm{\Lambda }}_b$ has recently been observed by the LHCb Collaboration at CERN. In contrast to most weak decays of $b$-flavored baryons, this process involves the decay of the strange quark in ${\mathrm{\Xi }}_b$ and thus has features in common with nonleptonic weak decays of hyperons. Thanks to the expected pure S-wave nature of the decay in question in the heavy $b$ quark limit, we find that its amplitude may be related to those for S-wave nonleptonic decays of $\mathrm{\Lambda }$, $\mathrm{\Sigma }$, and $\mathrm{\Xi }$ in a picture inspired by duality. The calculated branching fraction $\mathcal{B}({\mathrm{\Xi }}_b^{-}\to {\pi }^{-}{\mathrm{\Lambda }}_b)=(6.3\pm 4.2)\times {10}^{-3}$ is consistent with the range allowed in the LHCb analysis. The error is dominated by an assumed 30% uncertainty in the amplitude due to possible U(3) violation. A more optimistic view based on sum rules involving nonleptonic hyperon decay S-wave amplitudes reduces the error on the branching fraction to $2.0\times {10}^{-3}$.

We study all possible observables in $B\to D^{(*)}\tau {\nu }_{\tau }$ with new physics (NP), including new vector, scalar and tensor interactions, and investigate the prospects of extracting NP Wilson coefficients with optimal observables. The analysis shows that, overall, the full $q^2$ integrated observables in $B\to D\tau {\nu }_{\tau }$ are more sensitive towards the scalar current, whereas the bin-by-bin analysis of $q^2$ distribution of the differential branching fraction points to regions of $q^2$ sensitive to tensor interactions. Interestingly, the observables in $B\to D^{*}\tau {\nu }_{\tau }$ are more sensitive to tensor interactions, and bin-by-bin analysis of this mode shows the distinct regions of $q^2$ sensitive to vector or scalar interactions. In addition to that, the $\tau$ polarization asymmetry is found to be more sensitive to NP compared to the other observables, in both decay modes.

We analyze the impact of the carrier envelope phase on the differential cross sections of the Breit-Wheeler and the generalized Compton scattering in the interaction of a charged electron (positron) with an intensive ultrashort electromagnetic (laser) pulse. The differential cross sections as a function of the azimuthal angle of the outgoing electron have a clear bump structure, where the bump position coincides with the value of the carrier phase. This effect can be used for the carrier envelope phase determination.

We study the perturbative phase diagram of semisimple fermionic gauge theories resembling the Standard Model. We investigate an $SU(N)$ gauge theory with $M$ Dirac flavors where we gauge first an $SU(M{)}_L$ and then an $SU(2{)}_L\subset SU(M{)}_L$ of the original global symmetry $SU(M{)}_L\times SU(M{)}_R\times U(1)$ of the theory. To avoid gauge anomalies we add leptonlike particles. At the two-loop level an intriguing phase diagram appears. We uncover phases in which one, two or three fixed points exist and discuss the associated flows of the coupling constants. We discover a phase featuring complete asymptotic freedom and simultaneously an interacting infrared fixed point in both couplings. The analysis further reveals special renormalization group trajectories along which one coupling displays asymptotic freedom and the other asymptotic safety, while both flowing in the infrared to an interacting fixed point. These are safety free trajectories. We briefly sketch out possible phenomenological implications, among which an independent way to generate near-conformal dynamics à la walking is investigated.

Geodesic incompleteness is a problem in both general relativity and string theory. The Weyl-invariant Standard Model coupled to general relativity ($\mathrm{SM}+\mathrm{GR}$), and a similar treatment of string theory, are improved theories that are geodesically complete. A notable prediction of this approach is that there must be antigravity regions of spacetime connected to gravity regions through gravitational singularities such as those that occur in black holes and cosmological bang/crunch. Antigravity regions introduce apparent problems of ghosts that raise several questions of physical interpretation. It was shown that unitarity is not violated, but there may be an instability associated with negative kinetic energies in the antigravity regions. In this paper we show that the apparent problems can be resolved with the interpretation of the theory from the perspective of observers strictly in the gravity region. Such observers cannot experience the negative kinetic energy in antigravity directly, but can only detect in and out signals that interact with the antigravity region. This is no different from a spacetime black box for which the information about its interior is encoded in scattering amplitudes for in/out states at its exterior. Through examples we show that negative kinetic energy in antigravity presents no problems of principles but is an interesting topic for physical investigations of fundamental significance.

Real world quantum systems are open to perpetual influence from the wider environment. Quantum gravitational fluctuations provide a most fundamental source of the environmental influence through their universal interactions with all forms of energy and matter causing decoherence. This may have subtle implications on precision laboratory experiments and astronomical observations and could limit the ultimate capacities for quantum technologies prone to decoherence. To establish the essential physical mechanism of decoherence under weak spacetime fluctuations, we carry out a sequence of analytical steps utilizing the Dirac constraint quantization and gauge invariant influence functional techniques resulting in a general master equation of a compact form that describes an open quantum gravitational system with arbitrary bosonic fields. An initial application of the theory is illustrated by the implied quantum gravitational dissipation of light as well as (non)relativistic massive or massless scalar particles. Related effects could eventually lead to important physical consequences including those on a cosmological scale and for a large number of correlated particles.

We study the equations for the evolution of cosmological perturbations in $f(\mathcal{R})$ and conclude that this modified gravity model can be expressed as a dark energy fluid at background and linearized perturbation order. By eliminating the extra scalar degree of freedom known to be present in such theories, we are able to characterize the evolution of the perturbations in the scalar sector in terms of equations of state for the entropy perturbation and anisotropic stress which are written in terms of the density and velocity perturbations of the dark energy fluid and those in the matter, or the metric perturbations. We also do the same in the much simpler vector and tensor sectors. In order to illustrate the simplicity of this formulation, we numerically evolve perturbations in a small number of cases.

We study quasinormal modes of black holes in Lovelock gravity. We formulate the WKB method adapted to Lovelock gravity for the calculation of quasinormal frequencies (QNFs). As a demonstration, we calculate various QNFs of Lovelock black holes in seven and eight dimensions. We find that the QNFs show remarkable features depending on the coefficients of the Lovelock terms, the species of perturbations, and spacetime dimensions. In the case of the scalar field, when we increase the coefficient of the third order Lovelock term, the real part of QNFs increases, but the decay rate becomes small irrespective of the mass of the black hole. For small black holes, the decay rate ceases to depend on the Gauss-Bonnet term. In the case of tensor type perturbations of the metric field, the tendency of the real part of QNFs is opposite to that of the scalar field. The QNFs of vector type perturbations of the metric show no particular behavior. The behavior of QNFs of the scalar type perturbations of the metric field is similar to the vector type. However, available data are rather sparse, which indicates that the WKB method is not applicable to many models for this sector.

We show that the particle-number distribution of diamond modes, modes that are localized in a finite spacetime region, are thermal for the Minkowski vacuum state of a massless scalar field, an analogue to the Unruh effect. The temperature of the diamond is inversely proportional to its size. An inertial observer can detect this thermal radiation by coupling to the diamond modes using an appropriate energy-scaled detector. We further investigate the correlations between various diamonds and find that entanglement between adjacent diamonds dominates.

We consider spherically symmetric static composite structures consisting of a boson star and a global monopole, minimally or nonminimally coupled to the general relativistic gravitational field. In the nonminimally coupled case, Marunovic and Murkovic [Classical Quantum Gravity 31, 045010 (2014)] have shown that these objects, so-called topological-defect boson stars, can be sufficiently gravitationally compact so as to potentially mimic black holes. Here, we present the results of an extensive numerical parameter space survey which reveals additional new and unexpected phenomenology in the model. In particular, focusing on families of topological-defect boson stars which are parameterized by the central amplitude of the boson field, we find configurations for both the minimally and nonminimally coupled cases that contain one or more shells of bosonic matter located far from the origin. In parameter space, each shell spontaneously appears as one tunes through some critical central amplitude of the boson field. In some cases the shells apparently materialize at spatial infinity: in these instances their areal radii are observed to obey a universal scaling law in the vicinity of the critical amplitude. We derive this law from the equations of motion and the asymptotic behavior of the fields.

We study the application of a supersymmetric model with two constrained supermultiplets to inflationary cosmology. The first superfield $\mathbf{S}$ is a stabilizer chiral superfield satisfying a nilpotency condition of degree 2, ${\mathbf{S}}^2=0$. The second superfield $\mathbf{\Phi }$ is the inflaton chiral superfield, which can be combined into a real superfield $\mathbf{B}\equiv \frac{1}{2i}(\mathbf{\Phi }-\overline{\mathbf{\Phi }})$. The real superfield $\mathbf{B}$ is orthogonal to $\mathbf{S}$, $\mathbf{S}\mathbf{B}=0$, and satisfies a nilpotency condition of degree 3, ${\mathbf{B}}^3=0$. We show that these constraints remove from the spectrum the complex scalar sgoldstino, the real scalar inflaton partner (i.e. the “sinflaton”), and the fermionic inflatino. The corresponding supergravity model with de Sitter vacua describes a graviton, a massive gravitino, and one real scalar inflaton, with both the goldstino and inflatino being absent in unitary gauge. We also discuss relaxed superfield constraints where ${\mathbf{S}}^2=0$ and $\mathbf{S}\overline{\mathbf{\Phi }}$ is chiral, which removes the sgoldstino and inflatino, but leaves the sinflaton in the spectrum. The cosmological model building in both of these inflatino-less models offers some advantages over existing constructions.

In this paper, we study the Starobinsky model of inflation in the context of gravity’s rainbow theory. We propose that gravity rainbow functions can be written in the power-law form of the Hubble parameter. We present a detailed derivation of the spectral index of curvature perturbation and the tensor-to-scalar ratio and compare the predictions of our models with Planck 2015 data. We discover that in order to be consistent with Planck data up to $2\sigma$ C.L., the viable values of $N_k$ $e$-folds would satisfy $42\lesssim N_k\lesssim 87$ and the rainbow parameter $\lambda$ is nicely constrained to be $\lambda \lesssim 6.0$.

We explore two saddle point inflationary scenarios in the context of higher-order corrections related to different generalizations of general relativity. Firstly, we deal with the Jordan frame Starobinsky potential, for which we identify a portion of a parameter space of inflection point inflation, which can accommodate all the experimental results. Secondly, we analyze Higgs inflation and more specifically the influence of nonrenormalizible terms on the standard quartic potential. All results were verified with the Planck 2015 data.

All quintessence potentials that are either monotonic with negative interval or have a minimum at negative values of the potential, generically predict a future collapse of the scale factor to a “doomsday” singularity. We show that this doomsday is generically avoided in models with a proper nonminimal coupling of the quintessence scalar field to the curvature scalar $R$. For simplicity, we consider linear quintessence potential $V=-s\varphi$ and linear nonminimal coupling $F=1-\lambda \varphi$. However, our result is generic and is due to the fact that the nonminimal coupling modifies the effective potential that determines the dynamics of the scalar field. Thus, for each positive value of the parameter $s$, we find a critical value ${\lambda }_{\text{crit}}(s)$ such that for $\lambda >{\lambda }_{\text{crit}}(s)$ the negative potential energy does not dominate the Universe and the cosmic doomsday big crunch singularity is avoided because the scalar field eventually rolls up its potential. We find that ${\lambda }_{\text{crit}}(s)$ increases approximately linearly with $s$. For $\lambda >{\lambda }_{\text{crit}}(s)$ the potential energy of the scalar field becomes positive and it eventually dominates while the dark energy equation of state parameter tends to $w=-1$ leading to a de Sitter universe.

It has been shown in the last few years that three-form fields present viable cosmological solutions for inflation and dark energy with particular observable signatures distinct from those of canonical single scalar field inflation. The aim of this work is to explore the dynamics of a single three-form in a five-dimensional type II Randall-Sundrum braneworld scenario, in which a three-form is confined to the brane and only gravity propagates in the bulk. We compare the solutions with the standard four-dimensional case already studied in the literature. In particular, we evaluate how the spectral index and the ratio of tensor-to-scalar perturbations are influenced by the presence of the bulk and put constraints on the parameters of the models in light of the recent Planck 2015 data.

Modified gravity is considered to be one of the possible explanations of the accelerated expansions of the present and the early universe. We study the effects of modified gravity on big bang nucleosynthesis (BBN). If the effects of modified gravity are significant during the BBN epoch, they should be observed as changes of primordial light element abundances. We assume a $f(G)$ term with the Gauss-Bonnet term $G$, during the BBN epoch. A power-law relation of $df/dG\propto t^p$ where $t$ is the cosmic time was assumed for the function $f(G)$ as an example case. We solve time evolutions of physical variables during BBN in the $f(G)$ gravity model numerically, and we analyzed the calculated results. It is found that a proper solution for the cosmic expansion rate can be lost in some parameter region. In addition, we show that calculated results of primordial light element abundances can be significantly different from observational data. Especially, observational limits on the primordial D abundance leads to the strongest constraint on the $f(G)$ gravity. We then derive constraints on parameters of the $f(G)$ gravity taking into account the existence of the solution of expansion rate and final light element abundances.