By quantizing the background as well as the perturbations in a simple one fluid model, we show that there exists an ambiguity in the choice of relevant variables (assuming factor ordering to have been taken care of), potentially leading to incompatible observational physical predictions. There are, in such models, two fundamental ambiguities, a well-known one (factor ordering) which can be removed by an actual choice, and a new one, which depends on the choice of variables themselves. In a classical inflationary background, the exact same canonical transformations lead to unique predictions, so the ambiguity we put forward demands a background with a sufficiently strong departure from classical evolution. The latter condition happens to be satisfied in bouncing scenarios, which may thus be having predictability issues. Inflationary models could evade such a problem because of the monotonic behavior of their scale factor; they do, however, initiate from a singular state which bouncing scenarios aim at solving.

We discuss a coarse-graining procedure for describing the superhorizon dynamics of inflationary tensor modes. Using basic principles of quantum mechanics, we determine a probability density for coarse-grained tensor fields, which satisfies a stochastic Fokker-Planck equation. The corresponding noise and drift are computable, and depend on the cosmological system under consideration. Our general formulas are applied to a variety of cosmological scenarios, including cases seldom considered in the context of stochastic inflation. We start obtaining the expected expressions for noise and drift in pure de Sitter and power-law inflation, leading to a tensor spectrum whose properties match with quantum field theory calculations. We also discuss how a nonattractor phase during inflation influences the drift of our stochastic evolution equations. We then apply our method to scenarios with a transition from de Sitter to radiation and matter domination phases, for determining the stochastic distribution of superhorizon tensor modes during these eras. In particular, we show how interference effects between modes flowing through the cosmological horizon, and modes spontaneously produced at superhorizon scales, affect the stochastic evolution of coarse-grained quantities. The expression for the stochastic noise depends on the number of $e$-folds of cosmic evolution, and it rapidly approaches a constant after a few $e$-folds of postinflationary cosmic expansion. In an appropriate limit, the corresponding spectrum of tensor modes at horizon crossing matches with the results of quantum field theory calculations.

In the Penrose process and the Blandford-Znajek mechanism, the rotational energy of a black hole (BH) is extracted via particle fission and magnetic tension, respectively. Recently, inspired by a fundamental trait in plasma astrophysics known as magnetic reconnection (MR), a new energy extraction mechanism based on the fast reconnection of the magnetic field lines inside the ergosphere has been proposed by Comisso and Asenjo. In this paper, we investigate energy extraction caused by MR in the ergosphere of a rapidly spinning BH with broken Lorentz symmetry by a background bumblebee vector field. The desired rotating BH solution differentiates from the standard Kerr BH via the Lorentz symmetry breaking (LSB) parameter $l$, which comes from nonminimal coupling between the bumblebee field with nonzero vacuum expectation value and gravity. We find that incorporating $l<0$ in the background is in the interest of the energy extraction via MR for the fast-spinning BH surrounded by the plasma with weak magnetization, below what is expected from the scenario by Comisso and Asenjo. Our analysis robustly indicates that the power of energy extraction and efficiency of the plasma energization process through fast MR is more efficient than the Comisso-Asenjo solution, provided that the LSB parameter is negative, $l<0$. Compared to the Blandford-Znajek mechanism arising from the underlying background, we also show that MR is a more efficient energy extraction mechanism if $l<0$.

It was recently shown that a powerful beam of radio/microwave radiation sent out to space can produce detectable backscattering via the stimulated decay of ambient axion dark matter. This echo is a faint and narrow signal centered at an angular frequency close to half the axion mass. In this article, we provide a detailed analytical and numerical analysis of this signal, considering the effects of the axion velocity distribution as well as the outgoing beam shape. In agreement with the original proposal, we find that the divergence of the outgoing beam does not affect the echo signal, which is only constrained by the axion velocity distribution. Moreover, our findings are relevant for the optimization of the experimental parameters in order to attain maximal signal-to-noise ratio or minimal energy consumption.

We present a new gating method to remove non-Gaussian noise transients in gravitational-wave data. The method does not rely on any a priori knowledge on the amplitude or duration of the transient events. In light of the character of the newly released LIGO O3a data, glitch-identification is particularly relevant for searches using this data. Our method preserves more data than previously achieved, while obtaining the same, if not higher, noise reduction. We achieve a $\approx 2$-fold reduction in zeroed-out data with respect to the gates released by LIGO on the O3a data. We describe the method and characterise its performance. While developed in the context of searches for continuous signals, this method can be used to prepare gravitational-wave data for any search. As the cadence of compact-binary inspiral detections increases and the lower noise level of the instruments unveils new glitches, excising disturbances effectively, precisely, and in a timely manner, becomes more important. Our method does this. We release the source code associated with this new technique and the gates for the newly released O3 data.

The production of electron-positron pairs from light is a famous prediction of quantum electrodynamics. Yet it is often emphasized that the number of produced pairs has no physical meaning until the driving electromagnetic fields are switched off, as otherwise its definition is basis dependent. The common adiabatic definition, in particular, can predict the “creation” of a number of pairs orders of magnitude larger than the final yield. We show here, by clarifying exactly what is being counted, that the adiabatic number of pairs has an unambiguous and physical interpretation. As a result, and perhaps contrary to expectation, the large numbers of pairs seen at nonasymptotic times become, in principle, physically accessible.

We consider scalar extensions of the Standard Model (SM) and their effective field theoretic generalizations to illustrate the phenomenological connection between precision measurements of the anomalous magnetic moment of the muon $a_{\mu }$, precision Higgs measurements, and direct collider sensitivity. To this end, we consider charged beyond Standard Model (BSM) scalar sectors of the Zee-Babu type for which we develop a consistent and complete dimension-5 and -6 effective field theory extensions. This enables us to track generic new physics effects that interact with the SM predominantly via radiative interactions. While the operator space is high dimensional, the intersection of exotics searches at the Large Hadron Collider (LHC), Higgs signal strength, and anomalous muon magnetic measurements is manageably small. We find that consistency of LHC Higgs observations and $a_{\mu }$ requires a significant deformation of the new states’ electroweak properties. Evidence in searches for doubly charged scalars as currently pursued by the LHC experiments can be used to further tension the BSMEFT parameter space and resolve blind directions in the effective field theory (EFT)-extended Zee-Babu scenario.

We probe the cosmological consequences of a recently proposed class of solutions to the cosmological constant problem. In these models, the universe undergoes a long period of inflation followed by a contraction and a bounce that sets the stage for the hot big bang era. A requirement of any successful early universe model is that it must reproduce the observed scale-invariant density perturbations at cosmic microwave background (CMB) scales. While these class of models involve a long period of inflation, the inflationary Hubble scale during their observationally relevant stages is at or below the current Hubble scale, rendering the de Sitter fluctuations too weak to seed the CMB anisotropies. We show that sufficiently strong perturbations can still be sourced thermally if the relaxion field serving as the inflaton interacts with a thermal bath, which can be generated and maintained by the same interaction. We present a simple model where the relaxion field is derivatively (i.e., technically naturally) coupled to a non-Abelian gauge sector, which gets excited tachyonically and subsequently thermalizes due to its nonlinear self-interactions. This model explains both the smallness of the cosmological constant and the amplitude of CMB anisotropies.

We discuss the hard dense loop resummation at finite quark mass and evaluate the equation of state (EoS) of cold and dense QCD matter in $\beta$ equilibrium. The resummation in the quark sector has an effect of lowering the baryon number density and the EoS turns out to have much smaller uncertainty than the perturbative QCD estimate. Our numerical results favor smooth matching between the EoS from the resummed QCD calculation at high density and the extrapolated EoS from the nuclear matter density region. We also point out that the speed of sound in our EoS slightly exceeds the conformal limit.

A coupled-channel approach is applied to the charged tetraquark state $T_{cc}^{+}$ recently discovered by the LHCb Collaboration. The parameters of the interaction are fixed by a fit to the observed line shape in the three-body $D^0{D}^0{\pi }^{+}$ channel. Special attention is paid to the three-body dynamics in the $T_{cc}^{+}$ due to the finite life time of the $D^{*}$. An approach to the $T_{cc}^{+}$ is argued to be self-consistent only if both manifestations of the three-body dynamics, the pion exchange between the $D$ and $D^{*}$ mesons and the finite $D^{*}$ width, are taken into account simultaneously to ensure that three-body unitarity is preserved. This is especially important to precisely extract the pole position in the complex energy plane whose imaginary part is very sensitive to the details of the coupled-channel scheme employed. The $D^0{D}^0$ and $D^0{D}^{+}$ invariant mass distributions, predicted based on this analysis, are in good agreement with the LHCb data. The low-energy expansion of the $D^{*}D$ scattering amplitude is performed and the low-energy constants (the scattering length and effective range) are extracted. The compositeness parameter of the $T_{cc}^{+}$ is found to be close to unity, which implies that the $T_{cc}^{+}$ is a hadronic molecule generated by the interactions in the $D^{*+}{D}^0$ and $D^{*0}{D}^{+}$ channels. Employing heavy-quark spin symmetry, an isoscalar $D^{*}{D}^{*}$ molecular partner of the $T_{cc}^{+}$ with $J^P=1^{+}$ is predicted under the assumption that the $D{D}^{*}\text{−}{D}^{*}{D}^{*}$ coupled-channel effects can be neglected.

We discuss the processes $\pi \pi \to \pi \pi$ and $\pi \pi \to \pi \pi \gamma$ from a general quantum field theory (QFT) point of view. In the soft-photon limit where the photon energy $\omega \to 0$ we study the theorem due to F.E. Low. We confirm his result for the $1/\omega$ term of the $\pi \pi \to \pi \pi \gamma$ amplitude but disagree for the ${\omega }^0$ term. We analyze the origin of this discrepancy. Then we calculate the amplitudes for the above reactions in the tensor-Pomeron model. We identify places where “anomalous” soft photons could come from. Three soft-photon approximations (SPAs) are introduced. The corresponding SPA results are compared to those obtained from the full tensor-Pomeron model for c.m. energies $\sqrt{s}=10\mathrm{GeV}$ and 100 GeV. The kinematic regions where the SPAs are a good representation of the full amplitude are determined. Finally we make some remarks on the type of fundamental information one could obtain from high-energy exclusive hadronic reactions without and with soft photon radiation.

In [A. Tarasov and R. Venugopalan, Phys. Rev. D 102, 114022 (2020)], we demonstrated that the structure function $g_1(x_B,Q^2)$ measured in polarized deeply inelastic scattering (DIS) is dominated by the triangle anomaly in both Bjorken ($Q^2\to 0$) and Regge ($x_B\to 0$) asymptotics. In the worldline formulation of quantum field theory, the triangle anomaly arises from the imaginary part of the worldline effective action. We show explicitly how a Wess-Zumino-Witten term coupling the topological charge density to a primordial isosinglet $\overline{\eta }$ arises in this framework. We demonstrate the fundamental role played by this contribution both in topological mass generation of the ${\eta }^{\prime }$ and in the cancellation of the off-forward pole arising from the triangle anomaly in the proton’s helicity $\mathrm{\Sigma }(Q^2)$. We recover the striking result by Shore and Veneziano that $\mathrm{\Sigma }\propto \sqrt{{\chi }^{\prime }(0)}$, where ${\chi }^{\prime }$ is the slope of the QCD topological susceptibility in the forward limit. We construct an axionlike effective action for $g_1$ at small $x_B$ that describes the interplay between gluon saturation and the topology of the QCD vacuum. In articular, we outline the role of “over-the-barrier” sphaleronlike transitions in spin diffusion at small $x_B$. Such topological transitions can be measured in polarized DIS at a future Electron-Ion Collider.

Quarkonium suppression is one of the more useful observables to obtain information about the hot medium created in ultrarelativistic heavy-ion collisions. In this manuscript, we discuss a simple way to implement both the initial-state effects and the hot-medium evolution, and to compute the quarkonium nuclear modification factor if the survival probability for a bound state at a given energy density is known. Based on the Glauber model, the temperature of the evolving medium and the centrality dependence of the nuclear modification factor will be analyzed.

The genie neutrino Monte Carlo describes neutrino-induced hadronization with an effective model, known as Andreopoulos-Gallagher-Kehayias-Yang (agky), which is interfaced with pythia at high invariant mass. Only the low-mass agky model parameters were extracted from hadronic shower data from the FNAL 15 ft and BEBC experiments. In this paper, the first hadronization tune on averaged charged multiplicity data from deuterium and hydrogen bubble chamber experiments is presented, with a complete estimation of parameter uncertainties. A partial tune on deuterium data highlights the tensions between hydrogen and deuterium datasets.

The influence of the hard photon emission on the charge asymmetry in the lepton- and antilepton-proton elastic scattering was evaluated for the first time beyond the ultrarelativistic limit, while retaining the lepton mass at all steps of the calculation. This contribution—responsible for the charge asymmetry—is induced by interference between real photon emission from the lepton and proton. During the calculation any excited states of the intermediated proton were not considered, allowing us to use the standard fermionic propagator for this particle. The infrared divergence extracted using Lorenz-invariant approach of Bardin-Shumeiko is canceled by the corresponding soft part of the two-photon exchange contribution. Numerical analysis was performed within kinematic conditions of Jefferson Lab measurements and MUSE experiment in PSI.

Applying the techniques of light-front quantization to quantize a scalar field in a monochromatic gravitational wave background, we manage to investigate the response of the Unruh-DeWitt detector coupled to a scalar field in the presence of a gravitational wave for the two cases moving along a free-falling trajectory and a constant-accelerating trajectory. The transition rate of the Unruh-DeWitt detector, in both cases, is different from the result with no gravitational wave, and the leading-order correction due to the gravitational wave survives the long-wavelength limit that formally takes the wavelength of the gravitational wave to infinity. This new effect of the gravitational wave on a quantum system is qualitatively different from that on a classical mechanical system, and cannot be understood in terms of gravitational wave tidal force.