Simplified models provide an avenue for characterizing and exploring new physics for large classes of UV theories. In this article we study the ability of the LHC to probe the spin and parity quantum numbers of a new light resonance $X$ which couples predominantly to the third generation quarks in a variety of simplified models through the $t\overline{t}X$ channel. After evaluating the LHC discovery potential for $X$, we suggest several kinematic variables sensitive to the spin and $CP$ properties of the new resonance. We show how an analysis exploiting differential distributions in the semileptonic channel can discriminate among various possibilities. We find that the potential to discriminate a scalar from a pseudoscalar or (axial) vector to be particularly promising.

We present numerical details of the evaluation of the so-called Bose-ghost propagator in lattice minimal Landau gauge, for the SU(2) case in four Euclidean dimensions. This quantity has been proposed as a carrier of the confining force in the Gribov-Zwanziger approach and, as such, its infrared behavior could be relevant for the understanding of color confinement in Yang-Mills theories. Also, its nonzero value can be interpreted as direct evidence of Becchi-Rouet-Stora-Tyutin-symmetry breaking, which is induced when restricting the functional measure to the first Gribov region $\mathrm{\Omega }$. Our simulations are done for lattice volumes up to ${120}^4$ and for physical lattice extents up to 13.5 fm. We investigate the infinite-volume and continuum limits.

Motivated by the successes of covariant baryon chiral perturbation theory in one-baryon systems and in heavy-light systems, we study relevance of relativistic effects in hyperon-nucleon interactions with strangeness $S=-1$. In this exploratory work, we follow the covariant framework developed by Epelbaum and Gegelia to calculate the $YN$ scattering amplitude at leading order. By fitting the five low-energy constants to the experimental data, we find that the cutoff dependence is mitigated, compared with the heavy-baryon approach. Nevertheless, the description of the experimental data remains quantitatively similar at leading order.

$\mathrm{\Upsilon }(nS)$ and ${\chi }_b(nP)$ ($n=1$, 2, 3) production at the LHC is studied at next-to-leading order in ${\alpha }_s$ in nonrelativistic QCD. Feeddown contributions from higher ${\chi }_b$ and $\mathrm{\Upsilon }$ states are all considered for lower $\mathrm{\Upsilon }$ cross sections and polarizations. The long distance matrix elements (LDMEs) are extracted from the yield data, and then used to make predictions for the $\mathrm{\Upsilon }(nS)$ polarizations, which are found to be consistent with the measured polarization data within errors. In particular, the $\mathrm{\Upsilon }(3S)$ polarization puzzle can be understood by a large feeddown contribution from ${\chi }_b(3P)$ states. Our results may provide a good description for both cross sections and polarizations of prompt $\mathrm{\Upsilon }(nS)$ and ${\chi }_b(nP)$ production at the LHC.

Though not considered in general, purely baryonic decays could shed light on the puzzle of the baryon number asymmetry in the universe by means of a better understanding of the baryonic nature of our matter world. As such, they constitute a yet unexplored class of decay processes worth investigating. We propose to search for purely baryonic decay processes at the LHCb experiment. No such type of decay has ever been observed. In particular, we concentrate on the decay ${\mathrm{\Lambda }}_b^0\to p\overline{p}n$, which is the simplest purely baryonic decay mode, with solely spin-$1/2$ baryons involved. We predict its decay branching ratio to be $\mathcal{B}({\mathrm{\Lambda }}_b^0\to p\overline{p}n)=(2.0_{-0.2}^{+0.3})\times {10}^{-6}$, which is sufficiently large to make the decay mode accessible to LHCb. Our study can be extended to other purely baryonic decays such as ${\mathrm{\Lambda }}_b^0\to p\overline{p}\mathrm{\Lambda }$, ${\mathrm{\Lambda }}_b^0\to \mathrm{\Lambda }\overline{p}\mathrm{\Lambda }$, and ${\mathrm{\Lambda }}_b^0\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}\mathrm{\Lambda }$, as well as to similar decays of antitriplet $b$ baryons such as ${\mathrm{\Xi }}_b^{0,-}$.

We study the chiral phase transition in the presence of the chiral chemical potential ${\mu }_5$ using the two-flavor Nambu–Jona-Lasinio model. In particular, we analyze the reason why one can obtain two opposite behaviors of the chiral critical temperature as a function of ${\mu }_5$ in the framework of different regularization schemes. We compare the modifications of the chiral condensate and the critical temperature due to ${\mu }_5$ in different regularization schemes, analytically and numerically. Finally, we find that, for the conventional hard-cutoff regularization scheme, the increasing dependence of the critical temperature on the chiral chemical potential is an artifact, which is caused by the fact that it does not include a complete contribution from the thermal fluctuations. When the thermal contribution is fully taken into account, the chiral critical temperature should decrease with ${\mu }_5$.

We reconsider perturbative unitarity in quantum field theory and upgrade several arguments and results. The minimum assumptions that lead to the largest time equation, the cutting equations and the unitarity equation are identified. Using this knowledge and a special gauge, we give a new, simpler proof of perturbative unitarity in gauge theories and generalize it to quantum gravity, in four and higher dimensions. The special gauge interpolates between the Feynman gauge and the Coulomb gauge without double poles. When the Coulomb limit is approached, the unphysical particles drop out of the cuts and the cutting equations are consistently projected onto the physical subspace. The proof does not extend to nonlocal quantum field theories of gauge fields and gravity, whose unitarity remains uncertain.

We apply pseudospectral methods to integrate functional flow equations with high accuracy, extending earlier work on functional fixed point equations [J. Borchardt and B. Knorr, Phys. Rev. D 91, 105011 (2015)]. The advantages of our method are illustrated with the help of two classes of models: first, to make contact with literature, we investigate flows of the $\mathrm{O}(N)$ model in three dimensions, for $N=1$, 4 and in the large $N$ limit. For the case of a fractal dimension, $d=2.4$, and $N=1$, we follow the flow along a separatrix from a multicritical fixed point to the Wilson-Fisher fixed point over almost 13 orders of magnitude. As a second example, we consider flows of bounded quantum-mechanical potentials, which can be considered as a toy model for Higgs inflation. Such flows pose substantial numerical difficulties, and represent a perfect test bed to exemplify the power of pseudospectral methods.

In a recent paper, Buchbinder, Kirillova, and Pletnev presented formal arguments concerning the quantum equivalence of free massive antisymmetric tensor fields of the second and third rank to the free Proca theory and massive scalar field with minimal coupling to gravity, respectively. We confirm this result using explicit covariant calculations of nonlocal form factors based on the heart-kernel technique and discuss the discontinuity of quantum contributions in the massless limit.

In this paper we consider light-cone fluctuations arising as a consequence of the nontrivial topology of the locally flat cosmic string spacetime. By setting the light-cone along the $z$-direction we are able to develop a full analysis to calculate the renormalized graviton two-point function, as well as the mean square fluctuation in the geodesic interval function and the time delay (or advance) in the propagation of a light pulse. We found that all these expressions depend upon the parameter characterizing the conical topology of the cosmic string spacetime and vanish in the absence of it. We also point out that at large distances from the cosmic string the mean square fluctuation in the geodesic interval function is extremely small while in the opposite limit it logarithmically increases.

We propose a consistent analytic approach to the efficiency of collisional Penrose process in the vicinity of a maximally rotating Kerr black hole. We focus on a collision with arbitrarily high center-of-mass energy, which occurs if either of the colliding particles has its angular momentum fine-tuned to the critical value to enter the horizon. We show that if the fine-tuned particle is ingoing on the collision, the upper limit of the efficiency is $(2+\sqrt{3})(2-\sqrt{2})\simeq 2.186$, while if the fine-tuned particle is bounced back before the collision, the upper limit is $(2+\sqrt{3}{)}^2\simeq 13.93$. Despite earlier claims, the former can be attained for inverse Compton scattering if the fine-tuned particle is massive and starts at rest at infinity, while the latter can be attained for various particle reactions, such as inverse Compton scattering and pair annihilation, if the fine-tuned particle is either massless or highly relativistic at infinity. We discuss the difference between the present and earlier analyses.

According to statistical mechanics, microstates of an isolated physical system (say, a gas in a box) at time $t_0$ in a given macrostate of less-than-maximal entropy typically evolve in such a way that the entropy at time $t$ increases with $|t-t_0|$ in both time directions. In order to account for the observed entropy increase in only one time direction, the thermodynamic arrow of time, one usually appeals to the hypothesis that the initial state of the Universe was one of very low entropy. In certain recent models of cosmology, however, no hypothesis about the initial state of the Universe is invoked. We discuss how the emergence of a thermodynamic arrow of time in such models can nevertheless be compatible with the above-mentioned consequence of statistical mechanics, appearances to the contrary notwithstanding.

Many of the new physics models predict a light Higgs boson similar to the Higgs boson of the Standard Model (SM) and also extra scalar bosons. Beyond the search channels for a SM Higgs boson, the future collider experiments will explore additional channels that are specific to extended Higgs sectors. We study the charged Higgs boson production within the framework of two Higgs doublet models (THDM) in the proton-proton collisions at a future circular hadron collider (FCC-hh). With an integrated luminosity of $L_{\text{int}}=500{\mathrm{fb}}^{-1}$ at very high energy frontier ($\sqrt{s}=100\mathrm{TeV}$), we obtain a significant coverage of the parameter space and distinguish the charged Higgs-top-bottom interaction within the THDM or other new physics models with charged Higgs boson mass up to 1.5 TeV.

We investigate the charmed baryon production reaction $p\overline{p}\to {\mathrm{\Lambda }}_c{\overline{\mathrm{\Lambda }}}_c$ in the effective Lagrangian approach. Besides the $t$-channel $D^0$ and $D^{*0}$ mesons exchanges, the $s$-channel $Y(4630)$ meson exchange is taken into account. For the total cross sections, the $D^0$ and $D^{*0}$ mesons provide minor background contributions, while the $Y(4630)$ state gives a clear peak structure with the magnitude of $10\mu \mathrm{b}$ at center-of-mass energy 4.63 GeV. Based on the results, we suggest that the reaction of $p\overline{p}\to {\mathrm{\Lambda }}_c{\overline{\mathrm{\Lambda }}}_c$ can be used to search for the $1^{--}$ charmoniumlike $Y(4630)$ state, and our predictions may be tested in the future by the $\overline{\mathrm{P}}\mathrm{ANDA}$ facility.

We aim at drawing the hadron-quark phase transition line in the QCD phase diagram by using the two-phase model (TPM) in which the entanglement Polyakov-loop extended Nambu-Jona-Lasinio (EPNJL) model with the vector-type four-quark interaction is used for the quark phase and the relativistic mean field (RMF) model is used for the hadron phase. A reasonable TPM is constructed by using lattice QCD data and neutron star observations as reliable constraints. For the EPNJL model, we determine the strength of vector-type four-quark interaction at zero quark chemical potential from lattice QCD data on quark number density normalized by its Stefan-Boltzmann limit. For the hadron phase, we consider three RMF models: NL3; TM1; and the model proposed by Maruyama, Tatsumi, Endo, and Chiba (MTEC). We find that MTEC is most consistent with the neutron star observations and TM1 is the second best. Assuming that the hadron-quark phase transition occurs in the core of a neutron star, we explore the density dependence of vector-type four-quark interaction. Particularly for the critical baryon chemical potential ${\mu }_{\mathrm{B}}^{\mathrm{c}}$ at zero temperature, we determine a range of ${\mu }_{\mathrm{B}}^{\mathrm{c}}$ for the quark phase to occur in the core of a neutron star. The values of ${\mu }_{\mathrm{B}}^{\mathrm{c}}$ lie in the range $1560\mathrm{MeV}\le {\mu }_{\mathrm{B}}^{\mathrm{c}}\le 1910\mathrm{MeV}$.

The production rate of the X(5568) measured by the D0 collaboration is quite large and difficult to be understood by various general hadronization mechanism. We propose the inclusive production formulation for the cross section, and predict the distributions and production rates of X(5568) at LHC energies, which are crucial information for the relevant measurements. We also suspect $D_s^{\pm }{\pi }^{\pm }$ state can be copiously produced and observed.

Production of electron-positron pairs in the collision of a high-energy photon with a high-intensity few-cycle laser pulse is studied. By utilizing the frameworks of laser-dressed spinor and scalar quantum electrodynamics, a comparison between the production of pairs of Dirac and Klein-Gordon particles is drawn. Positron energy spectra and angular distributions are presented for various laser parameters. We identify conditions under which predictions from Klein-Gordon theory either closely resemble or largely differ from those of the proper Dirac theory. In particular, we address the question to which extent the relevance of spin effects is influenced by the short duration of the laser pulse.

We analyze a static and spherically symmetric hairy black hole solution in noninvariant massive gravity. The formalism of geometrothermodynamics is used to describe the thermodynamic characteristics of this black hole in a Legendre invariant way. For a black hole in massive gravity, the geometry of the space of equilibrium states is computed showing that it contains information about the thermodynamic interaction, critical points, and phase transitions structure.

We analyze the classical and quantum dynamics of a Bianchi I model in the presence of a small negative cosmological constant characterizing its evolution in term of the dust-time dualism. We demonstrate that in a canonical metric approach, the cosmological singularity is removed in correspondence to a positive defined value of the dust energy density. Furthermore, the quantum big bounce is connected to the Universe’s turning point via a well-defined semiclassical limit. Then we can reliably infer that the proposed scenario is compatible with a cyclical universe picture. We also show how, when the contribution of the dust energy density is sufficiently high, the proposed scenario can be extended to the Bianchi IX cosmology and therefore how it can be regarded as a paradigm for the generic cosmological model. Finally, we investigate the origin of the observed cutoff on the cosmological dynamics, demonstrating how the big-bounce evolution can be mimicked by the same semiclassical scenario, where the negative cosmological constant is replaced via a polymer discretization of the Universe’s volume. A direct proportionality law between these two parameters is then established.