Semiclassical chiral fermion models with Berry term are studied in a symplectic framework. In the free case, the system can be obtained from Souriau’s model for a relativistic massless spinning particle by “enslaving” the spin. The Berry term is identified with the classical spin two-form of the latter model. The Souriau model carries a natural Poincaré symmetry that we highlight, but spin enslavement breaks the boost symmetry. However the relation between the models allows us to derive a Poincaré symmetry of unconventional form for chiral fermions. Then we couple our system to an external electromagnetic field. For gyromagnetic ratio $g=0$ we get curious superluminal Hall-type motions; for $g=2$ and in a pure constant magnetic field in particular, we find instead spiraling motions.

Hořava gravity has been constructed so as to exhibit anisotropic scaling in the ultraviolet, as this renders the theory power-counting renormalizable. However, when coupled to matter, the theory has been shown to suffer from quadratic divergences. A way to cure these divergences is to add terms with both time and space derivatives. We consider this extended version of the theory in detail. We perform a perturbative analysis that includes all modes, determine the propagators and discuss how including mixed-derivative terms affects them. We also consider the Lifshitz scalar with mixed-derivative terms as a toy model for power counting arguments and discuss the influence of such terms on renormalizability.

We discuss the near singularity region of the linear mass Vaidya metric for massless particles with nonzero angular momentum. In particular we look at massless geodesics near the vanishing point of a special subclass of linear mass Vaidya metrics. We also investigate this same structure in the numerical solutions for the scattering of the Maxwell field from the singularity. In both cases we find that the null-singularity effectively becomes repulsive close to the final vanishing point leading us to argue that this metric could be plausibly used as a semiclassical model for the endpoint of black hole evaporation.

In this paper, we first review the equal area laws and Clapeyron equations in the extended phase space of charged anti–de Sitter black holes. With different fixed parameters, the Maxwell’s equal area law holds not only in the pressure-thermodynamic volume oscillatory line, but also in the charge-electric potential and temperature-entropy oscillatory lines. The conventional Clapeyron equation is generalized and two extra equations are found. Moreover, we show that the coexistence curve of the small and large charged black holes is charge independent in the reduced parameter space for any dimension of spacetime. The highly accurate fitting formula for the coexistence curve is also presented. Using this fitting formula of the coexistence curve, we find that the Clapeyron equations are highly consistent with the calculated values. The fitting formula is also very useful for further study on the thermodynamic property of the system varying along the coexistence curve.

We address the following question: To what extent can a quantum field tell if it has been placed in de Sitter space? Our approach is to use the techniques of nonequilibrium quantum field theory to compute the time evolution of a state which starts off in flat space for (conformal) times $\eta <{\eta }_0$ and then evolves in a de Sitter background turned on instantaneously at $\eta ={\eta }_0$. We find that the answer depends on what quantities one examines. We study a range of them, all based on two-point correlation functions, and analyze which ones approach the standard Bunch–Davies values over time. The outcome of this analysis suggests that the nature of the equilibration process in this system is similar to that in more familiar systems.

The long-awaited baryonic $B$ decay ${\overline{B}}^0\to p\overline{p}$ was recently observed by LHCb with a branching fraction of order $10^{-8}$. All the earlier model predictions are too large compared with experiment. In this work, we point out that for a given tree operator $O_i$, the contribution from its Fiertz transformed operator, an effect often missed in the literature, tends to cancel the internal $W$-emission amplitude induced from $O_i$. The wave function of low-lying baryons is symmetric in momenta and the quark flavor with the same chirality but antisymmetric in color indices. Using these symmetry properties and the chiral structure of weak interactions, we find that half of the Feynman diagrams responsible for internal $W$ emission cancel. Since this feature holds in the charmless modes but not in the charmful ones, we advocate that the partial cancellation accounts for the smallness of the tree-dominated charmless two-body baryonic $B$ decays. This also explains why most previous model calculations predicted too large rates as the above consideration was not taken into account. Finally, we emphasize that, contrary to the claim in the literature, the internal $W$-emission tree amplitude should be proportional to the Wilson coefficient $c_1+c_2$ rather than $c_1-c_2$.

We obtain the partial-wave unitarity constraints on dimension-six operators stemming from the analyses of vector boson and Higgs scattering processes as well as the inelastic scattering of standard model fermions into electroweak gauge bosons. We take into account all coupled channels, all possible helicity amplitudes, and explore a six-dimensional parameter space of anomalous couplings. Our analysis shows that for those operators affecting the Higgs couplings, present 90% confidence level constraints from global data analysis of Higgs and electroweak data are such that unitarity is not violated if $\sqrt{s}\le 3.2\mathrm{TeV}$. For the purely gauge-boson operator $O_{WWW}$, the present bounds from triple-gauge-boson analysis indicate that within its presently allowed 90% confidence level range unitarity can be violated in $f{\overline{f}}^{\prime }\to V{V}^{\prime }$ at center-of-mass energy $\sqrt{s}\ge 2.4\mathrm{TeV}$.

The measurement of a large like-sign dimuon asymmetry $A_{\mathrm{SL}}^b$ by the D0 experiment at the Tevatron departs noticeably from Standard Model (SM) expectations and it may be interpreted as a hint of physics beyond the Standard Model contributing to $\mathrm{\Delta }B\ne 0$ transitions. In this work we analyze how the natural suppression of $A_{\mathrm{SL}}^b$ in the SM can be circumvented by new physics. We consider generic Standard Model extensions where the charged current mixing matrix is enlarged with respect to the usual $3\times 3$ unitary Cabibbo-Kobayashi-Maskawa matrix, and show how, within this framework, a significant enhancement over Standard Model expectations for $A_{\mathrm{SL}}^b$ is easily reachable through enhancements of the semileptonic asymmetries $A_{\mathrm{SL}}^d$ and $A_{\mathrm{SL}}^s$ of both $B_d^0\text{−}{\overline{B}}_d^0$ and $B_s^0\text{−}{\overline{B}}_s^0$ systems. Despite being insufficient to reproduce the D0 measurement, such deviations from SM expectations may be probed by the LHCb experiment.

A simple model is used to demonstrate that the candidate tetraquark states $Z_b(10610)$, $Z_b(10650)$, $Z_c(3900)$, and $Z_c(4025)$ can be explained as coupled channel cusp effects. The model explains in a natural way the masses and quantum numbers of the putative states and the near equality of the widths of the $Z_b$ states. It is argued that the $Z_c(3900)$ and $Z_c(4025)$ should be visible in ${\overline{B}}^0\to J/\psi {\pi }^0{\pi }^0$ or $B^{-}\to J/\psi {\pi }^{-}{\pi }^0$, but should not appear in ${\overline{B}}^0\to J/\psi {\pi }^{+}{\pi }^{-}$, in agreement with recent LHCb results. Additional tests for cusp effects are suggested.

We discuss hadron mass corrections and threshold resummation for deep-inelastic scattering $\ell N\to {\ell }^{\prime }X$ and semi-inclusive annihilation $e^{+}{e}^{-}\to hX$ processes, and provide a prescription how to consistently combine these two corrections respecting all kinematic thresholds. We find an interesting interplay between threshold resummation and target mass corrections for deep-inelastic scattering at large values of Bjorken $x_B$. In semi-inclusive annihilation, on the contrary, the two considered corrections are relevant in different kinematic regions and do not affect each other. A detailed analysis is nonetheless of interest in light of recent high precision data from BABAR and BELLE on pion and kaon production, with which we compare our calculations. For both deep inelastic scattering and single inclusive annihilation, the size of the combined corrections compared to the precision of world data is shown to be large. Therefore, we conclude that these theoretical corrections are relevant for global QCD fits in order to extract precise parton distributions at large Bjorken $x_B$, and fragmentation functions over the whole kinematic range.

We apply the generalized Veneziano model ($B_5$ model) in the double-Regge exchange limit to the $\gamma p\to K^{+}{K}^{-}p$ reaction. Four different cases defined by the possible combinations of the signature factors of leading Regge exchanges [$(K^{*},a_2/f_2)$, $(K^{*},\rho /\omega )$, $(K_2^{*},a_2/f_2)$, and $(K_2^{*},\rho /\omega )$] have been simulated through the Monte Carlo method. Suitable event candidates for the double-Regge exchange high-energy limit were selected employing Van Hove plots as a better alternative to kinematical cuts in the $K^{+}{K}^{-}p$ Dalitz plot. In this way we predict and analyze the double-Regge contribution to the $K^{+}{K}^{-}p$ Dalitz plot, which constitutes one of the major backgrounds in the search for strangeonia, hybrids and exotics using $\gamma p\to K^{+}{K}^{-}p$ reaction. We expect that data currently under analysis, and those to come in the future, will allow verification of the double-Regge behavior and a better assessment of this component of the amplitude.

As one of the key components of perturbative QCD theory, it is helpful to find a systematic and reliable way to set the renormalization scale for a high-energy process. The conventional treatment is to take a typical momentum as the renormalization scale, which assigns an arbitrary range and an arbitrary systematic error to pQCD predictions, leading to the well-known renormalization scheme and scale ambiguities. As a practical solution for such a scale setting problem, the “principle of minimum sensitivity” (PMS) has been proposed in the literature. The PMS suggests to determine an optimal scale for the pQCD approximant of an observable by requiring its slope over the scheme and scale changes to vanish. In this paper, we present a detailed discussion on general properties of the PMS by utilizing three quantities $R_{e^{+}{e}^{-}}$, $R_{\tau }$ and $\mathrm{\Gamma }(H\to b\overline{b})$ up to four-loop QCD corrections. After applying the PMS, the accuracy of pQCD prediction, the pQCD convergence, the pQCD predictive power, etc., are discussed. Furthermore, we compare the PMS with another fundamental scale setting approach, i.e. the principle of maximum conformality (PMC). The PMC is theoretically sound, which follows the renormalization group equation to determine the running behavior of the coupling constant and satisfies the standard renormalization group invariance. Our results show that PMS does provide a practical way to set the effective scale for high-energy process, and the PMS prediction agrees with the PMC one by including enough high-order QCD corrections, both of which shall be more accurate than the prediction under the conventional scale setting. However, the PMS pQCD convergence is an accidental, which usually fails to achieve a correct prediction of unknown high-order contributions with next-to-leading order QCD correction only, i.e. it is always far from the “true” values predicted by including more high-order contributions.

In spite of the diversity in the equations of state of nuclear matter, the recently discovered I-Love-Q relations [Yagi and Yunes, Science 341, 365 (2013)], which relate the moment of inertia, tidal Love number (deformability), and the spin-induced quadrupole moment of compact stars, hold for various kinds of realistic neutron stars and quark stars. While the physical origin of such universality is still a current issue, the observation that the I-Love-Q relations of incompressible stars can well approximate those of realistic compact stars hints at a new direction to approach the problem. In this paper, by establishing recursive post-Minkowskian expansion for the moment of inertia and the tidal deformability of incompressible stars, we analytically derive the I-Love relation for incompressible stars and show that the so-obtained formula can be used to accurately predict the behavior of realistic compact stars from the Newtonian limit to the maximum mass limit.

We study a quantum field in elliptic de Sitter space ${\mathrm{dS}}_4/{\mathbb{Z}}_2$—the spacetime obtained from identifying antipodal points in ${\mathrm{dS}}_4$. We find that the operator algebra and Hilbert space cannot be defined for the entire space, but only for observable causal patches. This makes the system into an explicit realization of the horizon complementarity principle. In the absence of a global quantum theory, we propose a recipe for translating operators and states between observers. This translation involves information loss, in accordance with the fact that two observers see different patches of the spacetime. As a check, we recover the thermal state at the de Sitter temperature as a state that appears the same to all observers. This thermal state arises from the same functional that, in ordinary ${\mathrm{dS}}_4$, describes the Bunch-Davies vacuum.

We study the question of whether disentanglement of Hawking radiation can be achieved with any local operation. We assume that the operation we look for is unitary, from which follow restrictions on its action on basis vectors. This allows us to formulate requirements on the operation of disentanglement. We then show that these requirements can be fulfilled by a timelike boundary condition in the near-horizon area and that the local observer does not notice the presence of the boundary and does not encounter a firewall.

We apply Kaluza’s procedure to a metric version of Eddington-inspired Born-Infeld action in gravity in five dimensions. The resulting action contains, in addition to the usual four-dimensional actions for gravity and electromagnetism, nonlinear couplings between the electromagnetic field strength and curvature. Considering the spherically symmetric solution as an example, we find the lowest-order corrections for the Reissner-Nordström metric and the electromagnetic field.

Isocurvature perturbations in the inflationary literature typically involve quantum fluctuations of bosonic field degrees of freedom. In this work, we consider isocurvature perturbations from fermionic quantum fluctuations during inflation. When a stable massive fermion is coupled to a nonconformal sector different from the scalar metric perturbations, observably large amplitude scale invariant isocurvature perturbations can be generated. In addition to the computation of the isocurvature two-point function, an estimate of the local non-Gaussianities is also given and found to be promising for observations in a corner of the parameter space. The results provide a new class of cosmological probes for theories with stable massive fermions. On the technical side, we explicitly renormalize the composite operator in curved spacetime and show that gravitational Ward identities play an important role in suppressing certain contributions to the fermionic isocurvature perturbations.

We analyze the consequences of a disformal interaction between a massless scalar and matter particles in the context of atomic physics. We focus on the displacement of the atomic energy levels that it induces, and in particular the change in the Lamb shift between the 2s and 2p states. We find that the correction to the Lamb shift depends on the mass of the fermion orbiting around the nucleus, implying a larger effect for muonic atoms. Taking the cutoff scale describing the effective scalar field theory close to the QCD scale, we find that the disformal interaction can account for the observed difference in the proton radius of muonic versus electronic hydrogen. Explaining the proton radius puzzle is only possible when the scalar field is embedded in nonlinear theories which alleviate constraints from collider and stellar physics. Short distance properties of the Galileon where nonperturbative effects in vacuum are present ensure that unitarity is preserved in high-energy particle collisions. In matter, the chameleon mechanism alleviates the constraints on disformal interactions coming from the burning rates for stellar objects. We show how to combine these two properties in a single model which renders the proposed explanation of the proton radius puzzle viable.

We revisit constraints on the (pseudo)conformal universe from the nonobservation of statistical anisotropy in the Planck data. The quadratic maximal likelihood estimator is applied to the Planck temperature maps at frequencies 143 and 217 GHz as well as their cross-correlation. The strongest constraint is obtained in the scenario of the (pseudo)conformal universe with a long intermediate evolution after conformal symmetry breaking. In terms of the relevant parameter (coupling constant), the limit is $h^2<0.0013$ at 95% C.L. (using the cross estimator). The analogous limit is much weaker in the scenario without the intermediate stage ($h^2\ln \frac{H_0}{\mathrm{\Lambda }}<0.52$) allowing the coupling constant to be of order 1. In the latter case, the non-Gaussianity in the four-point function appears to be a more promising signature.

We compare two holographic arguments that impose especially strong bounds on the amount of inflation. One comes from the de Sitter equilibrium cosmology and the other from the work of Banks and Fischler. We find that simple versions of these two approaches yield the same bound on the number of e-foldings. A careful examination reveals that while these pictures are similar in spirit, they are not necessarily identical prescriptions. We apply the two pictures to specific cosmologies which expose potentially important differences and which also demonstrate ways these seemingly simple proposals can be tricky to implement in practice.