We propose a Gribov-Zwanziger type model action for the Landau-DeWitt gauge that preserves, for any gauge group, the invariance under background gauge transformations. At zero temperature, and to one-loop accuracy, the model can be related to the Gribov no-pole condition. We apply the model to the deconfinement transition in SU(2) and SU(3) Yang-Mills theories and compare the predictions obtained with a single or with various (color-dependent) Gribov parameters that can be introduced in the action without jeopardizing its background gauge invariance. The Gribov parameters associated to color directions orthogonal to the background can become negative, while keeping the background effective potential real. In some cases, the proper analysis of the transition requires the potential to be resolved in those regions.

We compute the homogeneous limit of nonhydrodynamic quasinormal modes (QNMs) of a phenomenologically realistic Einstein-Maxwell-Dilaton (EMD) holographic model for the quark-gluon plasma (QGP) that is able to i) quantitatively describe state-of-the-art lattice results for the QCD equation of state and higher-order baryon susceptibilities with $2+1$ flavors and physical quark masses up to the highest values of the baryon chemical potential currently reached in lattice simulations, ii) describe the nearly perfect fluidity of the strongly coupled QGP produced in ultrarelativistic heavy-ion collisions, and iii) give a very good description of the bulk viscosity extracted via some recent Bayesian analyses of hydrodynamical descriptions of heavy-ion experimental data. This EMD model has been recently used to predict the location of the QCD critical point in the QCD phase diagram, which was found to be within the reach of upcoming low-energy heavy-ion collisions. The lowest quasinormal modes of the $SO(3)$ rotationally invariant quintuplet, triplet, and singlet channels evaluated in the present work provide upper bounds for characteristic equilibration times describing how fast the dense medium returns to thermal equilibrium after being subjected to small disturbances. We find that the equilibration times in the different channels approach each other at high temperatures, but they are well separated at the critical point. Moreover, in most cases, these equilibration times decrease with increasing baryon chemical potential while keeping the temperature fixed.

The measurement of the mass of the $W$ boson is one of the most precise and impactful measurements to test the standard model (SM). Following the discovery of the Higgs boson and the measurement of its mass, all SM parameters are sufficiently well known in order to make precise predictions for electroweak observables such as the $W$ boson mass. These observables receive corrections in extensions of the SM. Experimentally, the dominant uncertainty in the $W$-boson mass measurement at hadron colliders arises due to parton distribution functions (PDFs). We present novel in situ methods of constraining the PDF variation and of reducing the PDF impact on the $W$-mass measurement uncertainty at hadron colliders. These methods can exploit the very high-statistics samples of $W$-boson candidate events at the LHC.

A search for new resonances decaying into jets containing $b$-hadrons in $pp$ collisions with the ATLAS detector at the LHC is presented in the dijet mass range from 0.57 to 7 TeV. The data set corresponds to an integrated luminosity of up to $36.1{\mathrm{fb}}^{-1}$ collected in 2015 and 2016 at $\sqrt{s}=13\mathrm{TeV}$. No evidence of a significant excess of events above the smooth background shape is found. Upper cross-section limits and lower limits on the corresponding signal mass parameters for several types of signal hypotheses are provided at 95% C.L. In addition, 95% C.L. upper limits are set on the cross sections for new processes that would produce Gaussian-shaped signals in the di-$b$-jet mass distributions.

A non-Hermitian operator may serve as the Hamiltonian for a unitary quantum system, if we can modify the Hilbert space of state vectors of the system so that it turns into a Hermitian operator. If this operator is time-dependent, the modified Hilbert space is generally time-dependent. This in turn leads to a generic conflict between the condition that the Hamiltonian is an observable of the system and that it generates a unitary time-evolution via the standard Schrödinger equation. We propose a geometric framework for addressing this problem. In particular we show that the Hamiltonian operator consists of a geometric part, which is determined by a metric-compatible connection on an underlying Hermitian vector bundle, and a nongeometric part which we identify with the energy observable. The same quantum system can be locally described using a time-dependent Hamiltonian that acts in a time-independent state space and is the sum of a geometric part and the energy operator. The full global description of the system is achieved within the framework of a moderate geometric extension of quantum mechanics where the role of the Hilbert space of state vectors is played by a Hermitian vector bundle $\mathcal{E}$ endowed with a metric compatible connection, and observables are given by global sections of a real vector bundle that is determined by $\mathcal{E}$. We examine the utility of our proposal to describe a class of two-level systems where $\mathcal{E}$ is a Hermitian vector bundle over a two-dimensional sphere.

We describe in detail the quantum tunneling of massive particles from Kerr black hole by using complex trajectories, which are solutions to Hamilton’s equations of motion with imaginary proper time. The trajectories are smooth and cover the inner and outer horizon regions. Following the worldline approach, we compute the energy flux at the event horizon as a summation over these complex trajectories. The density of states is given with the aid of Carter’s constant, and it is shown to be linear in momenta in the leading order, as long as the phase portrait of the system stays uniform. Under this assumption, we obtain the thermal spectrum $\sim (T_H^{+}{)}^4$.

We derive the complete set of geodesic equations for massive charged test particle and light motion in the five-dimensional, rotating and charged solution of the Einstein-Maxwell-Chern-Simons field equations in five-dimensional minimal gauged supergravity and present their analytical solutions. We study the polar and radial motion, depending on the spacetime and test particle parameters, and characterize the test particle motion qualitatively by the means of parametric plots and effective potentials. We use the analytical solutions in order to visualize the test particle motion by three-dimensional plots.

We consider critical Higgs inflation, namely, Higgs inflation with a rising inflection point at smaller field values than those of the plateau induced by the nonminimal coupling to gravity. It has been proposed that such a configuration is compatible with the present CMB observational constraints on inflation and also with primordial black hole production, accounting for the totality or a fraction of the observed dark matter. We study the model while taking into account the next-to-next-to-leading order (NNLO) corrections to the Higgs effective potential: such corrections are extremely important to reduce the theoretical error associated to the calculation. We find that, in the $3\sigma$ window for the relevant low energy parameters, which are the strong coupling and the Higgs mass (the top mass follows by requiring an inflection point), the potential at the inflection point is so large (and so is the Hubble constant during inflation) that the present bound on the tensor-to-scalar ratio is violated. The model is viable only when allowing the strong coupling to take its upper $3–4\sigma$ value. In our opinion, this tension shows that the model of critical Higgs inflation is likely to be not viable: neither inflation nor black holes as dark matter can be originated in this version of the model.

It is shown that the diagonalization of the axial-vector–pseudoscalar transitions in the effective meson Lagrangian in the presence of electromagnetic interactions leads to a deviation from the vector meson dominance picture which usually arises in the Nambu–Jona-Lasinio model. The essential features of such a modification of the theory are studied. Some important examples are considered in detail.

The nonlinear (strong-field) Breit-Wheeler $e^{+}{e}^{-}$ pair production by a probe photon traversing two consecutive short and ultrashort (subcycle) laser pulses is considered within a QED framework. The temporal shape of the pulses and the distance between them are essential for the differential cross section as a function of the azimuthal angle distribution of the outgoing electron (positron). The found effect of a pronounced azimuthal anisotropy is important for subcycle pulses and decreases rapidly with increasing width of the individual pulses.

We present a 13 TeV proton-proton collider simulation in a $\nu$-two-Higgs-doublet model. The heavy charged Higgs bosons are produced in pairs through the electroweak processes and decay to the light sterile neutrinos (lighter than the $W/Z$ boson masses). The light sterile neutrino further decays into a jet-like object with a muon in it. This helps us discriminate the signal from the backgrounds composed of the standard model jets.

Now that the $\mathrm{NO}\nu \mathrm{A}$ experiment has been running for a few years and has released some preliminary data, some constraints for the oscillation parameters can be inferred. The best fits for $\mathrm{NO}\nu \mathrm{A}$ include three degenerate results; the reason they are indistinct is that they produce almost degenerate probability curves. It has been postulated that these degeneracies can be resolved by running antineutrinos at $\mathrm{NO}\nu \mathrm{A}$ and/or combining its data with T2K. However, this degeneracy resolution power can be compromised if sterile neutrinos are present due to additional degrees of freedom that can significantly alter the oscillation probability for any of these best fits. We aim to investigate this degradation in predictive power and the effect of the DUNE experiment on it. In light of the 2018 $\mathrm{NO}\nu \mathrm{A}$ data, we also consider the same fits but with ${\theta }_{23}=45°$ to see if the sensitivity results are different.

We reassess the $B\to \pi \ell {\nu }_{\ell }$ differential branching ratio distribution experimental data released by the BABAR and Belle Collaborations supplemented with all lattice calculations of the $B\to \pi$ form factor shape available to date obtained by the HPQCD, FNAL/MILC, and RBC/UKQCD Collaborations. Our study is based on the method of Padé approximants and includes a detailed scrutiny of each individual data set that allows us to obtain $|V_{ub}|=3.51(8{)}_{\mathrm{stat}}(7{)}_{\mathrm{syst}}\times {10}^{-3}$. The semileptonic $B^{+}\to {\eta }^{(\prime )}{\ell }^{+}{\nu }_{\ell }$ decays are also addressed and the $\eta \text{−}{\eta }^{\prime }$ mixing discussed.

Inspired by a series of unexpected measurements of semileptonic decays mediated via $b\to c$ charged current interactions, we explore semileptonic $B_c$ decays to the four lightest $P$-wave charmonium states, ${\chi }_{c0},{\chi }_{c1},{\chi }_{c2},h_c$, by the recently developed improved perturbative QCD formalism, in which the charm quark mass effect is included both in the Sudakov factor and the hard kernels. We first directly evaluate the concerned transition form factors with vector and axial-vector currents in the region of small momentum transfer squared and then recast them to the full kinematical region by adopting the exponential parametrization. The obtained form factors are used to evaluate the semileptonic decay branching ratios, which can reach the order of ${10}^{-3}$, letting the corresponding measurement appear feasible. For a better analysis, a comparison of our results with the predictions of other models is provided. We also present the ratios between the tau and light lepton branching ratios and the polarization contributions in the relevant processes, which still need experimental tests in the ongoing and forthcoming experiments. Any significant deviations from the Standard Model results may provide some hints of new physics effects.

We study the instantons (or bounces) in the Brown-Teitelboim (BT) mechanism of relaxation of the cosmological constant which is a cosmological version of the Schwinger mechanism. The BT mechanism is a false vacuum decay of (anti–)de Sitter [$(\mathrm{A}){\mathrm{dS}}_{d+1}$] (and ${\mathbb{R}}^{1,d}$) spaces via spontaneous nucleations of spherical ($d-1$)-branes and thus ostensibly has bearings on $(\mathrm{A})\mathrm{d}{\mathrm{S}}_{d+1}/{\mathrm{CFT}}_d$ holography. In this paper, we focus on the four-dimensional case, although the higher- or lower-dimensional generalization is straightforward. As is the case with pair productions near black hole and de Sitter horizons, we show that the BT instanton action for a membrane nucleation encodes the thermodynamics of (anti–)de Sitter space. In particular, the membrane instanton precisely accounts for the change of entropy of (A)dS space before and after nucleation, in good accordance with ${\mathrm{AdS}}_{d+1}/{\mathrm{CFT}}_d$ in which the ($d-1$)-branes make up all degrees of freedom of ${\mathrm{AdS}}_{d+1}$ space. In light of this lesser-known perspective presented here, we also make remarks on 1) (A)dS/CFT and 2) complexity. For the complexity, we observe that the Lorentzian bounce action may have a close connection to complexity.

The Hulse-Taylor binary provides possibly the best test of GR to date. We find the modified quadrupole formula for infinite derivative gravity (IDG). We investigate the backreaction formula for propagation of gravitational waves, found previously for effective quantum gravity (EQG) for a flat background and extend this calculation to a de Sitter background for both EQG and IDG. We put tighter constraints on EQG using new LIGO data. We also find the power emitted by a binary system within the IDG framework for both circular and elliptical orbits and use the example of the Hulse-Taylor binary to show that IDG is consistent with GR.

The metric-affine variational principle is applied to generate teleparallel and symmetric teleparallel theories of gravity. From the latter we discover an exceptional class which is consistent with a vanishing affine connection. Based on this remarkable property, this work proposes a simpler geometrical formulation of general relativity that is oblivious to the affine spacetime structure, thus fundamentally depriving gravity of any inertial character. The resulting theory is described by the Hilbert action purged from the boundary term and is more robustly underpinned by the spin-2 field theory, where an extra symmetry is now manifest, possibly related to the double-copy structure of the gravity amplitudes. This construction also provides a novel starting point for modified gravity theories, and the paper presents new and simple generalizations where analytical self-accelerating cosmological solutions arise naturally in the early- and late-time Universe.

Linear perturbations for one parameter family of stationary, closed Nambu-Goto strings winding around a flat torus in the five-dimensional Schwarzschild spacetime have been studied. It has been shown that this problem is solvable in the sense that frequency spectra and perturbation modes can be expressed only with arithmetic operations and radicals. It has been proven that the Nambu-Goto strings belonging to this family are always unstable, no matter how they are located in an almost flat region distant from the event horizon.

The gravitational waveform of merging binary neutron stars encodes information about extreme states of matter. Probing these gravitational emissions requires the gravitational-wave detectors to have high sensitivity above 1 kHz. Fortunately for current advanced detectors, there is a sizeable gap between the quantum-limited sensitivity and the classical noise at high frequencies. Here we propose a detector design that closes such a gap by reducing the high-frequency quantum noise with an active optomechanical filter, frequency-dependent squeezing, and high optical power. The resulting noise level from 1 to 4 kHz approaches the current facility limit and is a factor of 20 to 30 below the design of existing advanced detectors. This will allow for precision measurements of (i) the postmerger signal of the binary neutron star, (ii) late-time inspiral, merger, and ringdown of low-mass black hole–neutron star systems, and possible detection of (iii) high-frequency modes during supernovae explosions. This design tries to maximize the science return of current facilities by achieving a sensitive frequency band that is complementary to the longer-baseline third-generation detectors: the 10 km Einstein Telescope and 40 km Cosmic Explorer. We have highlighted the main technical challenges towards realizing the design, which requires dedicated research programs. If demonstrated in current facilities, the techniques can be transferred to new facilities with longer baselines.

We discuss a covariant extension of interactions between scalar fields and fermions in a flat space-time. We show, in a covariant theory, how to evade fermionic ghosts appearing because of the extra degrees of freedom behind a fermionic nature even in the Lagrangian with first derivatives. We will give a concrete example of a quadratic theory with up to the first derivative of multiple scalar fields and a Weyl fermion. We examine not only the maximally degenerate condition, which makes the number of degrees of freedom correct, but also a supplementary condition guaranteeing that the time evolution takes place properly. We also show that proposed derivative interaction terms between scalar fields and a Weyl fermion cannot be removed by field redefinitions.