In the symmetric string fragmentation recipe adopted by PYTHIA for jet simulations, the transverse momenta of successive quarks are uncorrelated. This is a simplification but has no theoretical basis. Transverse momentum correlations are naturally expected, for instance, in a covariant multiperipheral model of quark hadronization. We propose a simple recipe of string fragmentation which leads to such correlations. The definition of the jet axis and its relation with the primordial transverse momentum of the quark is also discussed.

The process $e^{+}{e}^{-}\to \omega \eta {\pi }^0$ is studied in the energy range 1.45–2.00 GeV using data with an integrated luminosity of $33{\mathrm{pb}}^{-1}$ accumulated by the SND detector at the $e^{+}{e}^{-}$ collider VEPP-2000. The $e^{+}{e}^{-}\to \omega \eta {\pi }^0$ cross section is measured for the first time. The cross section has a threshold near 1.75 GeV. Its value is about 2 nb in the energy range 1.8–2.0 GeV. The dominant intermediate state for the process $e^{+}{e}^{-}\to \omega \eta {\pi }^0$ is found to be $\omega a_0(980)$.

The process $e^{+}{e}^{-}\to {\eta }^{\prime }J/\psi$ is observed for the first time with a statistical significance of $8.6\sigma$ at center-of-mass energy $\sqrt{s}=4.226\mathrm{GeV}$ and $7.3\sigma$ at $\sqrt{s}=4.258\mathrm{GeV}$ using data samples collected with the BESIII detector. The Born cross sections are measured to be $(3.7\pm 0.7\pm 0.3)$ and $(3.9\pm 0.8\pm 0.3)\mathrm{pb}$ at $\sqrt{s}=4.226$ and 4.258 GeV, respectively, where the first errors are statistical and the second systematic. Upper limits at the 90% confidence level of the Born cross sections are also reported at other 12 energy points.

We present a measurement of the total $WW$ and $WZ$ production cross sections in $p\overline{p}$ collision at $\sqrt{s}=1.96\mathrm{TeV}$, in a final state consistent with leptonic $W$ boson decay and jets originating from heavy-flavor quarks from either a $W$ or a $Z$ boson decay. This analysis uses the full data set collected with the CDF II detector during Run II of the Tevatron collider, corresponding to an integrated luminosity of $9.4{\mathrm{fb}}^{-1}$. An analysis of the dijet mass spectrum provides $3.7\sigma$ evidence of the summed production processes of either $WW$ or $WZ$ bosons with a measured total cross section of ${\sigma }_{WW+WZ}=13.7\pm 3.9\mathrm{pb}$. Independent measurements of the $WW$ and $WZ$ production cross sections are allowed by the different heavy-flavor decay patterns of the $W$ and $Z$ bosons and by the analysis of secondary-decay vertices reconstructed within heavy-flavor jets. The productions of $WW$ and of $WZ$ dibosons are independently seen with significances of $2.9\sigma$ and $2.1\sigma$, respectively, with total cross sections of ${\sigma }_{WW}=9.4\pm 4.2\mathrm{pb}$ and ${\sigma }_{WZ}=3.7_{-2.2}^{+2.5}\mathrm{pb}$. The measurements are consistent with standard-model predictions.

We verify the consistency of the Gödel-type solutions within the four-dimensional Chern-Simons modified gravity with the nondynamical Chern-Simons coefficient for different forms of matter including dust, fluid, scalar field, and electromagnetic field and discuss the related causality issues. We show that, unlike general relativity, a vacuum solution is possible in our theory. Another essentially new result of our theory having no analogue in general relativity consists in the existence of the hyperbolic causal solutions for a physically well-motivated matter.

We examine the time evolution of the frequencies of the gravitational wave after the bounce within the framework of relativistic linear perturbation theory using the results of one-dimensional numerical simulations of core-collapse supernovae. Protoneutron star models are constructed in such a way that the mass and the radius of the protoneutron star become equivalent to the results obtained from the numerical simulations. Then we find that the frequencies of gravitational waves radiating from protoneutron stars strongly depend on the mass and the radius of protoneutron stars, but almost independently of the profiles of the electron fraction and the entropy per baryon inside the star. Additionally, we find that the frequencies of gravitational waves can be characterized by the square root of the average density of the protoneutron star irrespective of the progenitor models, which are completely different from the empirical formula for cold neutron stars. The dependence of the spectra on the mass and the radius is different from that of the $g$-mode: the oscillations around the surface of protoneutron stars due to the convection and the standing accretion-shock instability. Careful observation of these modes of gravitational waves can determine the evolution of the mass and the radius of protoneutron stars after core bounce. Furthermore, the expected frequencies of gravitational waves are around a few hundred hertz in the early stages after bounce, which must be a good candidate for the ground-based gravitational wave detectors.

A special class of metrics, called universal metrics, solves all gravity theories defined by covariant field equations purely based on the metric tensor. Since we currently lack the knowledge of what the full quantum-corrected field equations of gravity are at a given microscopic length scale, these metrics are particularly important in understanding quantum fields in curved backgrounds in a consistent way. However, finding explicit universal metrics has been a difficult problem as there does not seem to be a procedure for it. In this work, we overcome this difficulty and give a construction of universal metrics of $d$-dimensional spacetime from curves constrained to live in a ($d-1$)-dimensional Minkowski spacetime or a Euclidean space.

Motivated by recent proposals of possible wormhole existence in galactic halos, we analyze the cosmological evolution of wormhole solutions in modified $f(R)$ gravity. We construct a dynamical wormhole that asymptotically approaches a Friedmann-Lemaître-Robertson-Walker (FLRW) universe, with supporting material going to the perfect isotropic fluid described by the equation of state for a radiation- and matter-dominated universe respectively. Our analysis is based on an approximation of a small wormhole—a wormhole that can be treated as matched with the FLRW metric at some radial coordinate much smaller than the Hubble radius, so that cosmological boundary conditions are satisfied. With a special interest in viable wormhole solutions, we refer to the results of the reconstruction procedure and use $f(R)$ functions which lead to the experimentally confirmed $\mathrm{\Lambda }\mathrm{CDM}$ expansion history of the Universe. Solutions we find imply no need for exotic matter near the throat of considered wormholes, while in the limit of $f(R)=R$ this need is always present during radiation- and matter-dominated epochs.

This paper deals with the propagation of Klein-Gordon particles in flat background spacetime exhibiting discontinuous metric changes from a Lorentzian signature $(-,+,+,+)$ to a Kleinian signature $(-,+,+,-)$. A formal analogy with the propagation of electrons at a junction between an anisotropic semiconductor and an electronic metamaterial is presented. From that analogy, we study the dynamics of these particles falling onto planar boundary interfaces between these two families of media and show a mirror-like behavior for the particle flux. Finally, the case of a double junction of finite thickness is examined and the possibility of tunneling through it is discussed. A physical link between the metamaterial and the Kleinian slabs is found by calculating the time of flight of the respective traversing particles.

We investigate the existence and phenomenology of stable photon orbits (SPOs) in stationary axisymmetric electrovacuum spacetimes in four dimensions. First, we review the classification of equatorial circular photon orbits on Kerr-Newman spacetimes in the charge-spin plane. Second, using a Hamiltonian formulation, we show that Reissner-Nordström diholes (a family encompassing the Majumdar-Papapetrou and Weyl-Bach special cases) admit SPOs, in a certain parameter regime that we investigate. Third, we explore the transition from order to chaos for typical SPOs bounded within a toroidal region around a dihole, via a selection of Poincaré sections. Finally, for general axisymmetric stationary spacetimes, we show that the Einstein-Maxwell field equations allow for the existence of SPOs in electro vacuum, but not in pure vacuum.

We present an asymptotically flat supersymmetric black lens solution with the horizon topology $L(n,1)=S^3/{\mathbb{Z}}_n$ in the five-dimensional minimal ungauged supergravity. We show that the black lens carries a mass, two independent angular momenta, electric charge, and ($n-1$) magnetic fluxes, among which only the $n+1$ quantities are independent.

Charged rotating Kerr-Newman black holes are known to be superradiantly unstable to perturbations of charged massive bosonic fields whose proper frequencies lie in the bounded regime $0<\omega <\min \{{\omega }_{\mathrm{c}}\equiv m{\mathrm{\Omega }}_{\mathrm{H}}+q{\mathrm{\Phi }}_{\mathrm{H}},\mu \}$, where $\{{\mathrm{\Omega }}_{\mathrm{H}},{\mathrm{\Phi }}_{\mathrm{H}}\}$ are, respectively, the angular velocity and electric potential of the Kerr-Newman black hole, and $\{m,q,\mu \}$ are, respectively, the azimuthal harmonic index, the charge-coupling constant, and the proper mass of the field. In this paper we study analytically the complex resonance spectrum which characterizes the dynamics of linearized charged massive scalar fields in a near-extremal Kerr-Newman black hole spacetime. Interestingly, it is shown that near the critical frequency ${\omega }_{\mathrm{c}}$ for superradiant amplification and in the eikonal large-mass regime, the superradiant instability growth rates of the explosive scalar fields are characterized by a nontrivial (nonmonotonic) dependence on the dimensionless charge-to-mass ratio $q/\mu$. In particular, for given parameters $\{M,Q,J\}$ of the central Kerr-Newman black hole, we determine analytically the optimal charge-to-mass ratio $q/\mu$ of the explosive scalar field which maximizes the growth rate of the superradiant instabilities in the composed Kerr-Newman-black-hole-charged-massive-scalar-field system.

We discuss the near-singularity region of the linear mass Vaidya metric. In particular, we investigate the structure in the numerical solutions for the scattering of scalar and electromagnetic metric perturbations from the singularity. We observe that, around the total evaporation point, quasinormal-like oscillations appear, indicating that this may be an interesting model for the description of the end point of black hole evaporation.

Recent blazar observations provide growing evidence for the presence of magnetic fields in the extragalactic regions. While natural speculation is to associate the production with inflationary physics, it is known that magnetogenesis solely from inflation is quite challenging. We therefore study a model in which a noninflaton field $\chi$ coupled to the electromagnetic field through its kinetic term, $-I^2(\chi )F^2/4$, continues to move after inflation until the completion of reheating. This leads to a postinflationary amplification of the electromagnetic field. We compute all the relevant contributions to the curvature perturbation, including gravitational interactions, and impose the constraints from the CMB scalar fluctuations on the strength of magnetic fields. We, for the first time, explicitly verify both the backreaction and CMB constraints in a simple yet successful magnetogenesis scenario without invoking a dedicated low-scale inflationary model in the weak-coupling regime of the kinetic coupling model.

Future ground-based cosmic microwave background (CMB) experiments will generate competitive large-scale structure data sets by precisely characterizing CMB secondary anisotropies over a large fraction of the sky. We describe a method for constraining the growth rate of structure to sub-1% precision out to $z\approx 1$, using a combination of galaxy cluster peculiar velocities measured using the kinetic Sunyaev-Zel’dovich (kSZ) effect, and the velocity field reconstructed from galaxy redshift surveys. We consider only thermal SZ-selected cluster samples, which will consist of $\mathcal{O}(10^4–10^5)$ sources for Stage 3 and 4 CMB experiments respectively. Three different methods for separating the kSZ effect from the primary CMB are compared, including a novel blind “constrained realization” method that improves signal-to-noise by a factor of $\sim 2$ over a commonly-used aperture photometry technique. Assuming a correlation between the integrated tSZ $y$-parameter and the cluster optical depth, it should then be possible to break the kSZ velocity-optical depth degeneracy. The effects of including CMB polarization and SZ profile uncertainties are also considered. In the absence of systematics, a combination of future Stage 4 experiments should be able to measure the product of the growth and expansion rates, $\alpha \equiv fH$, to better than 1% in bins of $\mathrm{\Delta }z=0.1$ out to $z\approx 1$—competitive with contemporary redshift-space distortion constraints from galaxy surveys. We conclude with a discussion of the likely impact of various systematics.

We study dynamics of cosmological models with diffusion effects modeling dark matter and dark energy interactions. We show the simple model with diffusion between the cosmological constant sector and dark matter, where the canonical scaling law of dark matter $({\rho }_{dm,0}{a}^{-3}(t))$ is modified by an additive $\epsilon (t)=\gamma t{a}^{-3}(t)$ to the form ${\rho }_{dm}={\rho }_{dm,0}{a}^{-3}(t)+\epsilon (t)$. We reduced this model to the autonomous dynamical system and investigate it using dynamical system methods. This system possesses a two-dimensional invariant submanifold on which the dark matter-dark energy (DM-DE) interaction can be analyzed on the phase plane. The state variables are density parameter for matter (dark and visible) and parameter $\delta$ characterizing the rate of growth of energy transfer between the dark sectors. A corresponding dynamical system belongs to a general class of jungle type of cosmologies represented by coupled cosmological models in a Lotka-Volterra framework. We demonstrate that the de Sitter solution is a global attractor for all trajectories in the phase space and there are two repellers: the Einstein-de Sitter universe and the de Sitter universe state dominating by the diffusion effects. We distinguish in the phase space trajectories, which become in good agreement with the data. They should intersect a rectangle with sides of ${\mathrm{\Omega }}_{m,0}\in [0.2724,0.3624]$, $\delta \in [0.0000,0.0364]$ at the 95% CL. Our model could solve some of the puzzles of the $\mathrm{\Lambda }\mathrm{CDM}$ model, such as the coincidence and fine-tuning problems. In the context of the coincidence problem, our model can explain the present ratio of ${\rho }_m$ to ${\rho }_{de}$, which is equal $0.4576_{-0.0831}^{+0.1109}$ at a $2\sigma$ confidence level.

During their propagation through intergalactic space, ultrahigh energy cosmic rays (UHECRs) interact with the background radiation fields. These interactions give rise to energetic electron/positron pairs and photons which in turn feed electromagnetic cascades, contributing to the isotropic gamma-ray background (IGRB). The gamma-ray flux level generated in this way highly depends upon the UHECR propagation distance, as well as the evolution of their sources with redshift. Recently, the Fermi-LAT Collaboration reported that the majority of the total extragalactic gamma-ray flux originates from extragalactic point sources. This posits a stringent upper limit on the IGRB generated via UHECR propagation, and subsequently constrains their abundance in the distant Universe. Focusing on the contribution of UHECR at energies below the ankle within a narrow energy band ($(1–4)\times {10}^{18}\mathrm{eV}$), we calculate the diffuse gamma-ray flux generated through UHECR propagation, normalizing the total cosmic ray energy budget in this band to that measured. We find that in order to not over-produce the new IGRB limit, a local “fog” of UHECR produced by nearby sources may exist, with a possible non-negligible contribution from our Galaxy. Following the assumption that a given fraction of the observed IGRB at 820 GeV originates from UHECR, we obtain a constraint on the maximum distance for the majority of their sources. With other unresolved source populations still contaminating the new IGRB limit, and UHECR above the ankle invariably contributing also to this background, the results presented here are rather conservative.

We demonstrate the importance of including the lensing contribution in galaxy clustering analyses with large galaxy redshift surveys. It is well known that radial cross-correlations between different redshift bins of galaxy surveys are dominated by lensing. But we show here that also neglecting lensing in the autocorrelations within one bin severely biases cosmological parameter estimation with redshift surveys. It leads to significant shifts for several cosmological parameters, most notably the scalar spectral index and the neutrino mass scale. Especially the latter parameter is one of the main targets of future galaxy surveys.

We study the magnetic field effect on chiral phase transition in a Nambu–Jona-Lasinio model. In comparison with a mean-field approximation containing only quarks, including mesons as quantum fluctuations in the model leads to a transition from inverse to delayed magnetic catalysis at finite temperature and delays the transition at finite baryon chemical potential. The location of the critical end point depends nonmonotonically on the magnetic field.

We consider the $SU(6)$ grand unified theory (GUT) model as an explanation for the diphoton final state excess, where the masses of all associated particles are linked with a new symmetry breaking scale. In this model, the diphoton final states arise due to loops involving three pairs of new vectorlike particles having the same quantum numbers as down-type quarks and lepton doublets. These new vectorlike fermions are embedded alongside the standard model (SM) fermions into minimal anomaly-free representations of the $SU(6)$ gauge symmetry. The $SU(6)$ symmetry is broken to the standard model times $U(1{)}_X$ at the GUT scale, and masses for the vectorlike fermions arise at the TeV scale only after the residual $U(1{)}_X$ symmetry is broken. The vectorlike fermions do not acquire masses via breaking of the SM symmetry at the electroweak scale. The field which is responsible for the newly observed resonance belongs to the ${\overline{6}}_H$ representation. The dark matter arises from the SM singlet fermion residing in $\overline{6}$ and is of Majorana type. We explicitly demonstrate gauge coupling unification in this model, and also discuss the origin of neutrino masses. In addition to the diphoton final states, we make distinctive predictions for other final states which are likewise accessible to the ongoing LHC experimental effort.