We study the question of whether two frames of a given physical theory are equivalent or not in the presence of quantum corrections. By using field theory arguments, we claim that equivalence is broken in the presence of anomalous symmetries in one of the frames. This is particularized to the case of the relation between the Einstein and Jordan frames in scalar-tensor theories used to describe early Universe dynamics. Although in this case a regularization that cancels the anomaly exists, the renormalized theory always develops a nonvanishing contribution to the S matrix that is present only in the Jordan frame, promoting the different frames to different physical theories that must be UV completed in a different way.

By using the Faddeev-Popov quantization procedure, we demonstrate that the radiative effects computed using the first-order and second-order Einstein-Hilbert action for general relativity are the same, provided one can discard tadpoles. In addition, we show that the first-order form of this action can be used to obtain a set of Feynman rules that involves just two propagating fields and three three-point vertices; using these rules is considerably simpler than employing the infinite number of vertices that occur in the second-order form. We demonstrate this by computing the one-loop, two-point function.

We analyze the ($3+1$)D equilibrium chiral magnetic effect (CME). We apply derivative expansion to the Wigner transform of the two-point Green function. This technique allows us to express the response of electric current to the external electromagnetic field strength through the momentum space topological invariant. We consider the wide class of the lattice regularizations of quantum field theory (that includes, in particular, the regularization with Wilson fermions) and also certain lattice models of solid state physics (including those of Dirac semimetals). It appears that in these models the mentioned topological invariant vanishes identically at nonzero chiral chemical potential. That means that the bulk equilibrium CME is absent in those systems.

We show that for a general four derivative theory of gravity, only the holographic entanglement entropy functionals obey the second law at linearized order in perturbations. We also derive bounds on the higher curvature couplings in several examples, demanding the validity of the second law for higher order perturbations. For the five-dimensional Gauss-Bonnet theory in the context of AdS/CFT, the bound arising from black branes coincides with there being no sound channel instability close to the horizon. Repeating the analysis for topological black holes, the bound coincides with the tensor channel causality constraint (which is responsible for the viscosity bound). Furthermore, we show how to recover the holographic $c$-theorems in higher curvature theories from similar considerations based on the Raychaudhuri equation.

It is concluded in the literature that the Ellis wormhole is unstable under small perturbations and would either decay to the Schwarzschild black hole or expand away to infinity. While this deterministic conclusion of instability is correct, we show that the Ellis wormhole reduces to the Schwarzschild black hole only when the Ellis solution parameter $\gamma$ assumes a complex value $-i$. We shall then reexamine the stability of Ellis and phantom wormholes from the viewpoint of local and asymptotic observers by using a completely different approach, viz., we adapt Tangherlini’s nondeterministic, prequantal statistical simulation about photon motion in the real optical medium to an effective medium reformulation of motions obtained via Hamilton’s optical-mechanical analogy in a gravity field. A crucial component of Tangherlini’s idea is the observed increase of momentum of the photons entering a real medium. We show that this fact has a heuristic parallel in the effective medium version of the Pound-Rebka experiment in gravity. Our conclusion is that there is a nonzero probability that Ellis and phantom wormholes could appear stable or unstable depending on the location of observers and on the values of $\gamma$, leading to the possibility of ghost wormholes (like ghost stars). The Schwarzschild horizon, however, would always certainly appear to be stable ($R=1$, $T=0$) to observers regardless of their location. Phantom wormholes of bounded mass in the extreme limit $a\to -1$ are also shown to be stable just as the Schwarzschild black hole is. We shall propose a thought experiment showing that our nondeterministic results could be numerically translated into observable deterministic signatures of ghost wormholes.

We evaluate the one-loop partition function of conformal gravity in four dimensions around an ${\mathrm{AdS}}_4$ background, using the heat kernel techniques. We give expressions for the relevant thermodynamical quantities and compare our results with those from the literature.

The post-inflationary evolution of inflation-produced magnetic fields, conventional or not, can change dramatically when two fundamental issues are accounted for. The first is causality, which demands that local physical processes can never affect superhorizon perturbations. The second is the nature of the transition from inflation to reheating and then to the radiation era, which determine the initial conditions at the start of these epochs. Causality implies that inflationary magnetic fields do not freeze into the matter until they have re-entered the causal horizon. The nature of the cosmological transitions and the associated initial conditions, on the other hand, determine the large-scale magnetic evolution after inflation. Put together, the two can slow down the adiabatic magnetic decay on superhorizon scales throughout the Universe’s post-inflationary evolution and thus lead to considerably stronger residual magnetic fields. This is “good news” for both the conventional and the nonconventional scenarios of cosmic magnetogenesis. Mechanisms operating outside standard electromagnetism, in particular, do not need to enhance their fields too much during inflation in order to produce seeds that can feed the galactic dynamo today. In fact, even conventionally produced inflationary magnetic fields might be able to sustain the dynamo.

We show that when a supernova explodes, a nearby pulsar signal goes through a very specific change. The observed period first changes smoothly, then is followed by a sudden change in the time derivative. A stable millisecond pulsar can allow us to measure such an effect. This may improve our measurement of the total energy released in neutrinos and also the orientation of the supernova-pulsar system.

Ward-Green-Takahashi (WGT) identities play a crucial role in hadron physics, e.g. imposing stringent relationships between the kernels of the one- and two-body problems, which must be preserved in any veracious treatment of mesons as bound states. In this connection, one may view the dressed gluon-quark vertex, ${\mathrm{\Gamma }}_{\mu }^a$, as fundamental. We use a novel representation of ${\mathrm{\Gamma }}_{\mu }^a$, in terms of the gluon-quark scattering matrix, to develop a method capable of elucidating the unique quark-antiquark Bethe-Salpeter kernel, $\mathcal{K}$, that is symmetry consistent with a given quark gap equation. A strength of the scheme is its ability to expose and capitalize on graphic symmetries within the kernels. This is displayed in an analysis that reveals the origin of $H$-diagrams in $\mathcal{K}$, which are two-particle-irreducible contributions, generated as two-loop diagrams involving the three-gluon vertex, that cannot be absorbed as a dressing of ${\mathrm{\Gamma }}_{\mu }^a$ in a Bethe-Salpeter kernel nor expressed as a member of the class of crossed-box diagrams. Thus, there are no general circumstances under which the WGT identities essential for a valid description of mesons can be preserved by a Bethe-Salpeter kernel obtained simply by dressing both gluon-quark vertices in a ladderlike truncation; and, moreover, adding any number of similarly dressed crossed-box diagrams cannot improve the situation.

Tensor network (TN) methods, in particular the matrix product states (MPS) ansatz, have proven to be a useful tool in analyzing the properties of lattice gauge theories. They allow for a very good precision, much better than standard Monte Carlo (MC) techniques for the models that have been studied so far, due to the possibility of reaching much smaller lattice spacings. The real reason for the interest in the TN approach, however, is its ability, shown so far in several condensed matter models, to deal with theories which exhibit the notorious sign problem in MC simulations. This makes it prospective for dealing with the nonzero chemical potential in QCD and other lattice gauge theories, as well as with real-time simulations. In this paper, using matrix product operators, we extend our analysis of the Schwinger model at zero temperature to show the feasibility of this approach also at finite temperature. This is an important step on the way to deal with the sign problem of QCD. We analyze in detail the chiral symmetry breaking in the massless and massive cases and show that the method works very well and gives good control over a broad range of temperatures, essentially from zero to infinite temperature.

In this study, we calculated the dependence of thermodynamic observables, namely, pressure, baryon number density, and baryon susceptibility, on the baryon chemical potential ${\mu }_B$ through lattice quantum chromodynamics using the canonical approach. We compare the results with those obtained using the multiparameter reweighting (MPR) method. The results of these methods were found to be in very good agreement in the regions where the errors of the MPR method are under control. The canonical method yields reliable results up to ${\mu }_B/T=3$, where $T$ is the temperature. Multiple precision operations play important roles in the evaluation of canonical partition functions.

The Drell-Yan (DY) process of dilepton pair production off nuclei is not affected by final state interactions, energy loss, or absorption. A detailed phenomenological study of this process is thus convenient for investigation of the onset of initial-state effects in proton-nucleus ($pA$) collisions. In this paper, we present a comprehensive analysis of the DY process in $pA$ interactions at RHIC and LHC energies in the color dipole framework. We analyze several effects affecting the nuclear suppression, $R_{pA}<1$, of dilepton pairs, such as the saturation effects, restrictions imposed by energy conservation (the initial-state effective energy loss), and the gluon shadowing, as a function of the rapidity, the invariant mass of the dileptons, and their transverse momenta $p_T$. In this analysis, we take into account not only the ${\gamma }^{*}$ but also the $Z^0$ contribution to the production cross section, thus extending the predictions to large dilepton invariant masses. Besides the nuclear attenuation of produced dileptons at large energies and forward rapidities emerging due to the onset of shadowing effects, we predict a strong suppression at large $p_T$, dilepton invariant masses, and Feynman variable $x_F$ caused by the initial-state interaction effects in kinematic regions where no shadowing is expected. The manifestations of nuclear effects are also investigated in terms of the correlation function in the azimuthal angle between the dilepton pair and a forward pion $\mathrm{\Delta }\varphi$ for different energies, dilepton rapidities, and invariant dilepton masses. We predict that the characteristic double-peak structure of the correlation function around $\mathrm{\Delta }\varphi \simeq \pi$ arises for very forward pions and large-mass dilepton pairs.

The possible existence of Majorana neutrinos can be tested through the study of processes where the total lepton number $L$ is violated by two units ($\mathrm{\Delta }L=2$). In this work, the production of an on-shell Majorana neutrino with a mass around $\sim 0.2\mathrm{GeV}$ to a few GeV is studied in $\mathrm{\Delta }L=2$ decays of the $B_c$ meson. We focus on the same-sign di-muon channels: three-body $B_c^{-}\to {\pi }^{+}{\mu }^{-}{\mu }^{-}$ and four-body $B_c^{-}\to J/\psi {\pi }^{+}{\mu }^{-}{\mu }^{-}$ and their experimental sensitivity at the LHCb. In both channels, we find that sensitivities on the branching fraction of the order $\lesssim {10}^{-7}({10}^{-8})$ might be accessible at the LHC run 2 (future LHC run 3), allowing us to set additional and complementary constraints on the parameter space associated with the mass and mixings of the Majorana neutrino. In particular, bounds can be obtained on the mixing $|V_{\mu N}{|}^2\sim \mathcal{O}({10}^{-5}–{10}^{-4})$ that are similar or better that the ones obtained from heavy meson $\mathrm{\Delta }L=2$ decays: $D_{(s)}^{-}\to {\pi }^{+}{\mu }^{-}{\mu }^{-}$ and $B^{-}\to {\pi }^{+}{\mu }^{-}{\mu }^{-}(D^0{\pi }^{+}{\mu }^{-}{\mu }^{-})$.

We study parameter degeneracies that can occur in long-baseline neutrino appearance experiments due to nonstandard interactions (NSI) in neutrino propagation. For a single off-diagonal NSI parameter, and neutrino and antineutrino measurements at a single $L/E$, there exists a continuous four-fold degeneracy (related to the mass hierarchy and ${\theta }_{23}$ octant) that renders the mass hierarchy, octant, and $CP$ phase unknowable. Even with a combination of $\mathrm{NO}\nu \mathrm{A}$ and T2K data, which in principle can resolve the degeneracy, both NSI and the $CP$ phase remain unconstrained because of experimental uncertainties. A wide-band beam experiment like DUNE will resolve this degeneracy if the nonzero off-diagonal NSI parameter is ${\epsilon }_{e\mu }$. If ${\epsilon }_{e\tau }$ is nonzero, or the diagonal NSI parameter ${\epsilon }_{ee}$ is $\mathcal{O}(1)$, a wrong determination of the mass hierarchy and of $CP$ violation can occur at DUNE. The octant degeneracy can be further complicated by ${\epsilon }_{e\tau }$, but is not affected by ${\epsilon }_{ee}$.

Uncertainties in modeling neutrino-nucleus interactions are a major contribution to systematic errors in long-baseline neutrino oscillation experiments. Accurate modeling of neutrino interactions requires additional experimental observables such as the Adler angles which carry information about the polarization of the $\mathrm{\Delta }$ resonance and the interference with nonresonant single pion production. The Adler angles were measured with limited statistics in bubble chamber neutrino experiments as well as in electron-proton scattering experiments. We discuss the viability of measuring these angles in neutrino interactions with nuclei.

A scheme is presented to cancel out topologically unfactorized infrared divergences in the inclusive production of heavy quarkonia, which affect the nonrelativistic QCD (NRQCD) factorization of these processes. Heavy quarkonia are defined as resonance states of QCD instead of a color-singlet heavy quark pair. Thus the final heavy quark pair is not necessarily a color singlet. In addition, heavy quarkonia are reconstructed from their decay products. As a result, the transitions between states containing heavy quarks caused by exchanges of soft gluons are also taken into account here. Such cancellation is crucial for the NRQCD factorization of these processes.

In the context of a broad class of quenched models, we derive a generalized differential form of the Kadanoff-Baym (KB) ansatz which relates the out of equilibrium correlated and spectral Green’s functions. This relation holds at any time both before the quench (when it coincides with the fluctuation-dissipation theorem) as well as after it. We also examine, in the context of exactly soluble quenched models, the validity of some of the earlier alternative extensions of the KB ansatz.

We consider a toy model for the relativistic collapse of a homogeneous perfect fluid that takes into account an equation of state for high density matter, in the form of a Hagedorn phase, and semiclassical corrections in the strong field. We show that collapse reaches a critical minimum size and then bounces. We discuss the conditions needed for the collapse to halt and form a compact object. We argue that implications of models such as the one presented here are of great importance for astrophysics as they show that black holes may not be the only final outcome of collapse of very massive stars.

We exploit the near-horizon conformal symmetry of rapidly spinning black holes to determine universal properties of their magnetospheres. Analytic expressions are derived for the limiting form of the magnetosphere in the near-horizon region. The symmetry is shown to imply that the black hole Meissner effect holds for free Maxwell fields but is generically violated for force-free fields. We further show that in the extremal limit, near-horizon plasma particles are infinitely boosted relative to accretion flow. Active galactic nuclei powered by rapidly spinning black holes are therefore natural sites for high-energy particle collisions.

We consider Detweiler’s redshift variable $z$ for a nonspinning mass $m_1$ in circular motion (with orbital frequency $\mathrm{\Omega }$) around a nonspinning mass $m_2$. We show how the combination of effective-one-body (EOB) theory with the first law of binary dynamics allows one to derive a simple, exact expression for the functional dependence of $z$ on the (gauge-invariant) EOB gravitational potential $u=(m_1+m_2)/R$. We then use the recently obtained high-post-Newtonian(PN)-order knowledge of the main EOB radial potential $A(u;\nu )$ [where $\nu =m_1{m}_2/(m_1+m_2{)}^2$] to decompose the second-self-force-order contribution to the function $z(m_2\mathrm{\Omega },m_1/m_2)$ into a known part (which goes beyond the 4PN level in including the 5PN logarithmic term and the 5.5PN contribution) and an unknown one [depending on the yet unknown, 5PN, $6\mathrm{PN},\dots$, contributions to the $O({\nu }^2)$ contribution to the EOB radial potential $A(u;\nu )$]. We apply our results to the second-self-force-order contribution to the frequency shift of the last stable orbit. We indicate the expected singular behaviors, near the lightring, of the second-self-force-order contributions to both the redshift and the EOB $A$ potential. Our results should help both in extracting information of direct dynamical significance from ongoing second-self-force-order computations and in parametrizing their global strong-field behaviors. We also advocate computing second-self-force-order conservative quantities by iterating the time-symmetric Green-function in the background spacetime.