We revisit the evaluations for the spacelike and timelike $\rho \pi$ transition form factors $F_{\rho \pi }(Q^2)$ and $G_{\rho \pi }(Q^2)$ with the inclusion of the next-to-leading order (NLO) QCD contributions in the framework of the $k_T$-factorization theorem. The infrared divergence is regularized by the transversal momentum carried by external valence quarks, and ultimately absorbed into the meson wave functions. In the region of $Q^2\le 2{\mathrm{GeV}}^2$, where the perturbative QCD factorization approach is applicable, the NLO contribution can bring no larger than 35% enhancement to the spacelike form factor $F_{\rho \pi }(Q^2)$. For the timelike form factor derived under the kinematic exchanging symmetry, this contribution is also under control when the momentum transfer squared is large enough. We also prolong our prediction into the small $Q^2$ region by taking the lattice QCD results into account, and subsequently obtain the coupling $g_{\rho \pi \gamma }=G_{\rho \pi }(0)=0.596$.

The first search for double charged charmoniumlike state production in $\mathrm{\Upsilon }(1S)$ and $\mathrm{\Upsilon }(2S)$ decays and in $e^{+}{e}^{-}$ annihilation at $\sqrt{s}=10.52$, 10.58, and 10.867 GeV is conducted using data collected with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant signals are observed in any of the studied modes, and the 90% credibility level upper limits on their product branching fractions in $\mathrm{\Upsilon }(1S)$ and $\mathrm{\Upsilon }(2S)$ decays [$\mathcal{B}(\mathrm{\Upsilon }(1S,2S)\to Z_c^{+}{Z}_c^{(\prime )-})\times \mathcal{B}(Z_c^{+}\to {\pi }^{+}+c\overline{c})$ ($c\overline{c}=J/\psi$, ${\chi }_{c1}(1P)$, $\psi (2S)$)] and the product of Born cross section and branching fraction for $e^{+}{e}^{-}\to Z_c^{+}{Z}_c^{(\prime )-}$ ($\sigma (e^{+}{e}^{-}\to Z_c^{+}{Z}_c^{(\prime )-})\times \mathcal{B}(Z_c^{+}\to {\pi }^{+}+c\overline{c})$) at $\sqrt{s}=10.52$, 10.58, and 10.867 GeV are determined. Here, $Z_c$ refers to the $Z_c(3900)$ and $Z_c(4200)$ observed in the $\pi J/\psi$ final state, the $Z_{c1}(4050)$ and $Z_{c2}(4250)$ in the $\pi {\chi }_{c1}(1P)$ final state, and the $Z_c(4050)$ and $Z_c(4430)$ in the $\pi \psi (2S)$ final state.

We investigate the speed of sound in ($d+1$)-dimensional quantum field theory by studying its dual ($d+2$)-dimensional gravity theory from gauge/gravity correspondence. Instead of the well-known conformal limit $c_s^2\to 1/d$ at high temperature, we reveal two more universal quantities in various limits: $c_s^2\to (d-1)/16\pi$ at low temperature and $c_s^2\to (d-1)/16\pi d$ at large chemical potential.

We study holographic conformal anomalies and the corresponding $a$-theorem for Einstein gravity extended with Horndeski terms that involve up to and including linear curvature tensors. We focus on our discussion in $D=5$ bulk dimensions. For the generic Horndeski coupling, the $a$-charge is the same as that in Einstein gravity, but the inclusion of the Horndeski term violates the $a$-theorem. However, there exists a critical point of the Horndeski coupling, for which the theory admits nearly anti–de Sitter (AdS) spacetimes with nonvanishing Horndeski scalar. The full AdS isometry is broken down by the logarithmic scalar hair to the Poincaré group plus the scale invariance. We find that in this case the $a$-charge depends on the AdS radius $\ell$ and the integration constant ${\chi }_s$ of the Horndeski scalar. In addition, we find that two new central charges emerge, that are absent in gravities with minimally coupled matter. We call them $b$-charges. These $b$-charges also depend on $\ell$ and ${\chi }_s$. We construct an $a$-function for fixed $\ell$ but with the running Horndeski scalar $\chi$ replacing the constant ${\chi }_s$, and establish the holographic $a$-theorem using the null energy condition in the bulk. Furthermore, we find that there exist analogous monotonous $b$-functions as well. We also obtain the $a$-charge and the $a$-theorem in general odd bulk dimensions.

We give a definition of uncomplexity of a mixed state without invoking any particular definitions of mixed state complexity and argue that it gives the amount of computational power Bob has when he only has access to part of a system. We find geometric meanings of our definition in various black hole examples and make a connection with subregion duality. We show that Bob’s uncomplexity is the portion of his accessible interior spacetime inside his entanglement wedge. This solves a puzzle we encountered about the uncomplexity of the thermofield double state. In this process, we identify different kinds of operations Bob can do as being responsible for the growth of different parts of spacetime.

We present a new technique for computing entanglement harvesting with Unruh-DeWitt particle detectors. The method is particularly useful in cases where analytic solutions are rare and the Wightman function is known only via its mode expansion for which numerical integration can become very expensive. By exploiting the conjugate symmetry of the Wightman function, we may split the integral into parts dependent on the commutator and anticommutator of the field. In cases where the commutator vanishes, such as spacelike separation, or timelike separation if the strong Huygens principle holds, we then show that the entangling term of the bipartite density matrix can be expressed in terms of the much simpler mutual information term. For the vacuum state, this can be translated into a simple Fourier transform, and thus a single sum over modes, simplifying the procurement of closed expressions. We demonstrate this for Minkowski space, finding an analytical solution where none was previously known.

In a previous work we suggested a self-gravitating electromagnetic monopole solution in a string-inspired model involving global spontaneous breaking of a SO(3) internal symmetry and Kalb-Ramond (KR) axions, stemming from an antisymmetric tensor field in the massless string multiplet. These axions carry a charge, which, in our model, also plays the role of the magnetic charge. The resulting geometry is close to that of a Reissner-Nordström (RN) black hole with charge proportional to the KR-axion charge. We proposed the existence of a thin shell structure surrounding a (large inner) core as the dominant mass contribution to the energy functional. Although the resulting energy was finite, and proportional to the KR-axion charge, the size of the shell was not determined and left as a phenomenological parameter. In the current article, we propose a new way to calculate the size of the thin shell: string theory considerations suggest that the short-distance physics inside the inner core may be dominated by a positive cosmological constant term proportional to the scale of the spontaneous symmetry breaking of SO(3). The size of the shell is estimated by matching the RN metric of the shell to the de Sitter metric inside the core. The matching entails the Israel junction conditions for the metric and its first derivatives at the inner boundary of the shell, and determines the inner mass-shell radius. The axion charge plays an important role in guaranteeing the positivity of the “mass coefficient” of the gravitational potential term appearing in the metric; so, the KR electromagnetic monopole shows normal attractive gravitational effects. This is to be contrasted with the axion-less global monopole case where such a matching is known to yield a negative “mass coefficient” (and, hence, a repulsive gravitational effect). The total energy of our monopole within the shell is calculated. As a result of the violation of Birkhoff’s theorem (due to the formal divergence of the energy functional in the absence of a large distance cutoff), the total energy does not have to equal the mass coefficient. However, for phenomenologically relevant sets of parameters, the ratio of the total energy and the mass coefficient in the shell is close to 1. The gravitational “effective mass coefficient” in the shell can be made equal to the total energy outside the core by a small decrease in the cosmological constant in the de Sitter region. This is achieved through a dilaton potential which is suitably negative inside the de-Sitter region, but vanishes outside that region.

We find hairy black holes of Einstein-Maxwell theory with a complex scalar field that is confined inside a box in a Minkowski background. These regular hairy black holes are asymptotically flat, and thus the presence of the box or mirror allows us to evade well-known no-hair theorems. We also find the Israel surface stress tensor that the confining box must have to obey the energy conditions. In the zero horizon radius limit, these hairy black holes reduce to a regular asymptotically flat hairy soliton. We find our solutions using perturbation theory. At leading order, a hairy black hole can be seen as a Reissner-Nordstrom black hole placed on top of a hairy soliton with the same chemical potential (so that the system is in thermodynamic equilibrium). The hairy black holes merge with the Reissner-Nordstrom black hole family at the onset of the superradiant instability. When they coexist, for a given energy and electric charge, hairy black holes have higher entropy than caged Reissner-Nordstrom black holes. Therefore, our hairy black holes are the natural candidates for the end point of charged superradiance in the Reissner-Nordstrom black hole mirror system.

We give a full analysis of the conservation along null surfaces of generalized energy and supermomenta, for gravitational systems enclosed by a finite boundary. In particular, we interpret the conservation equations in a canonical manner, revealing a notion of symplectic potential and a boundary current intrinsic to null surfaces. This generalizes similar analyses done at asymptotic infinity or on horizons.

In a flat spacetime with one spatial dimension compactified, inertial reference frames are not all equivalent, but there are the preferred ones. This paper investigates the nonequivalence of inertial frames and also that of uniformly accelerated frames in connection with the response of the Unruh-DeWitt detector coupled to a massless scalar field. The detector’s transition rates of both excitation and deexcitation are studied in depth for three different cases: (i) the detector moving at an arbitrary constant velocity, (ii) moving with a constant acceleration in the compact direction, and (iii) moving with a constant acceleration in noncompact directions. The instantaneous transition rate in relation to the switching function is also taken into account.

The radiation emitted by horizonless exotic compact objects (ECOs), such as wormholes, 2-2-holes, fuzzballs, gravastars, boson stars, collapsed polymers, superspinars etc., is expected to be strongly suppressed when compared to the radiation of black holes. If large primordial curvature fluctuations collapse into such objects instead of black holes, they do not evaporate or evaporate much slower than black holes and could thus constitute all of the dark matter with masses below $M<{10}^{-16}{M}_{\odot }$. We reevaluate the relevant experimental constraints for light ECOs in this mass range and show that very large new parameter space down to ECO masses $M\sim 10\mathrm{TeV}$ opens up for light primordial dark matter. A new dedicated experimental program is needed to test this mass range of primordial dark matter.

Slow-roll solutions to inflationary potentials have been widely believed to be the only universal attractor. Over the past few years there has been growing interest in a new class of inflationary models known as constant-roll inflation. Constant-roll solutions are a generalization of “ultraslow roll” dynamics, where the first slow-roll parameter is small, but the second slow-roll parameter $\eta$ is larger than unity. In ultraslow roll inflation, the large-$\eta$ solution is a dynamical transient, relaxing exponentially to the attractor de Sitter solution. In the constant-roll generalization, recent papers have concluded that constant-roll inflation represents a new class of nonslow roll attractor solutions. In this paper we show that these attractor solutions are actually the usual slow-roll attractor, disguised by a parameter duality, and that the large-$\eta$ solutions, as in the case of ultraslow roll, represent a dynamical transient.

Scalar fields provide attractive modifications of pre-BBN cosmology, which have interesting implications for dark matter abundances. We analyze the effect of these modifications on the number of $e$-foldings between the horizon exit of cosmic microwave background modes and the end of inflation $(N_k)$, and examine the consequences for inflationary predictions of various models. We find significant effects in the predictions in the $(n_s,r)$ plane. For a large part of the parameter space, the shift in $N_k$ is positive; this ameliorates the tension of $m^2{\phi }^2$ and natural inflation with data.

In the context of quantum cosmology and the Wheeler-DeWitt equation, we investigate the possible effects of a non-semiclassical wave function of the Universe on the evolution of the inflationary perturbations. These are associated with the quantum behavior of the homogenous degrees of freedom (in particular the radius of the Universe) in the early stages of the inflationary expansion, which in turn can affect the dynamics of the trans-Planckian modes of the fields present. The existence of a bounce for the homogeneous gravitational wave function is studied. This can lead to an interference between a contracting and an expanding universe and, as a consequence, to the above quantum gravitational effects on the primordial spectra. In the traditional study of the inflationary fluctuations, such effects are neglected and a quasiclassical behavior for the homogeneous inflaton-gravity system is taken.

A scale-invariant universe can have a period of accelerated expansion at early times: inflation. We use a frame-invariant approach to calculate inflationary observables in a scale-invariant theory of gravity involving two scalar fields: the spectral indices, the tensor-to-scalar ratio, the level of isocurvature modes, and non-Gaussianity. We show that scale symmetry leads to an exact cancellation of isocurvature modes and that, in the scale symmetry–broken phase, this theory is well described by a single scalar-field theory. We find the predictions of this theory strongly compatible with current observations.

Spectra of cosmic rays (CRs), and particularly their features, contain a lot of important information about the astroparticle physics and the fundamental physics. Realizing that the 4 PeV knee of CR nuclei and the 1 TeV spectral cutoff of the electron share almost the same Lorentz factor, we propose that CRs experience a threshold interaction with a new light particle $X$ abundant in the Galaxy. The interaction $\mathrm{CR}+X\to \mathrm{CR}+X^{\prime }$ can take place when the effective energy is sufficient to convert it into another heavier unknown particle $X^{\prime }$ (as a representative to all possible threshold inelastic interactions). Under this scenario, we can reproduce the spectral break for both the nuclei and the electron and predict a zigzag spectrum for them. Given that there are great uncertainties in experiments, our model accommodates a wide mass range of the $X$ from the ultralow value to around 1 eV.

We explore the phenomenology of having a second epoch of dark matter annihilation into dark radiation long after the standard thermal freeze-out. Such a hidden reannihilation process could affect visible sectors only gravitationally. As a concrete realization we consider self-interacting dark matter (SIDM) with a light force mediator coupled to dark radiation. We demonstrate how resonantly Sommerfeld enhanced cross sections emerge to induce the reannihilation epoch. The effect is a temporally local modification of the Hubble expansion rate, and we show that the cosmic microwave background (CMB) measurements—as well as other observations—have a high sensitivity to observe this phenomenon. Special attention is given to the model region where late kinetic decoupling and strong self-interactions can alleviate several small-scale problems in the cold dark matter paradigm at the same time. Interestingly, we find that reannihilation might here also simultaneously lower the tension between CMB and low-redshift astronomical observations of $H_0$ and ${\sigma }_8$. Moreover, we identify reannihilation as a clear signature to discriminate between the phenomenologically otherwise almost identical vector and scalar mediator realizations of SIDM.

We study a scenario where sterile neutrino (either warm or cold) dark matter (DM) is produced through (nonresonant) oscillations among right-handed neutrinos (RHNs) and can constitute the whole DM in the Universe, in contrast to the conventional sterile neutrino production through its mixing with the left-handed neutrinos. The lightest RHN can be sterile neutrino DM whose mixing with left-handed neutrinos is sufficiently small while heavier RHNs can have non-negligible mixings with left-handed neutrinos to explain the neutrino masses by the seesaw mechanism. We also demonstrate that, in our scenario, the production of sterile RHN DM from the decay of a heavier RHN is subdominant compared with the RHN oscillation production due to the x-ray and small-scale structure constraints.

We generalize models invoking a spin-2 particle as a mediator between the dark sector and the standard model. We show that a massive spin-2 messenger can efficiently play the role of a portal between the two sectors. The dark matter is then produced via a freeze-in mechanism during the reheating epoch. In a large part of the parameter space, production through the exchange of a massive spin-2 mediator dominates over processes involving a graviton with Planck suppressed couplings. We perform a systematic analysis of such models for different values of the spin-2 mass relative to the maximum and the final temperature attained at reheating.

Recent $b\to s\ell \ell$ anomalies may imply the existence of a new $Z^{\prime }$ boson with left-handed $Z^{\prime }bs$ and $Z^{\prime }\mu \mu$ couplings. Such a $Z^{\prime }$ may be directly observed at LHC via $b\overline{s}\to Z^{\prime }\to {\mu }^{+}{\mu }^{-}$, and its relevance to $b\to s\ell \ell$ may be studied by searching for the process $gs\to Z^{\prime }b\to {\mu }^{+}{\mu }^{-}b$. In this paper, we analyze the capability of the 14 TeV LHC to observe the $Z^{\prime }$ in the ${\mu }^{+}{\mu }^{-}$ and ${\mu }^{+}{\mu }^{-}b$ modes based on an effective model with major phenomenological constraints imposed. We find that both modes can be discovered with $3000{\mathrm{fb}}^{-1}$ data if the $Z^{\prime }bs$ coupling saturates the latest $B_s-{\overline{B}}_s$ mixing limit from UTfit at around $2\sigma$. Besides, a tiny right-handed $Z^{\prime }bs$ coupling, if it exists, opens up the possibility of a relatively large left-handed counterpart, due to cancellation in the $B_s-{\overline{B}}_s$ mixing amplitude. In this case, we show that even a data sample of $\mathcal{O}(100){\mathrm{fb}}^{-1}$ would enable discovery of both modes. We further study the impact of a $Z^{\prime }bb$ coupling as large as the $Z^{\prime }bs$ coupling. This scenario enables discovery of the $Z^{\prime }$ in both modes with milder effects on the $B_s-{\overline{B}}_s$ mixing, but obscures the relevance of the $Z^{\prime }$ to $b\to s\ell \ell$. Discrimination between the $Z^{\prime }bs$ and $Z^{\prime }bb$ couplings may come from the production cross section for the $Z^{\prime }b\overline{b}$ final state. However, we do not find the prospect for this to be promising.