We investigate deviations from the plane wave model in the interaction of charged particles with strong electromagnetic fields. A general result is that integrability of the dynamics is lost when going from lightlike to timelike or spacelike field dependence. For a special scenario in the classical regime we show how the radiation spectrum in the spacelike (undulator) case becomes well-approximated by the plane wave model in the high-energy limit, despite the two systems being Lorentz inequivalent. In the quantum problem, there is no analogue of the WKB-exact Volkov solution. Nevertheless, WKB and uniform-WKB approaches give good approximations in all cases considered. Other approaches that reduce the underlying differential equations from second to first order are found to miss the correct physics for situations corresponding to barrier transmission and wide-angle scattering.

We present an integral formalism for constructing scheme transformations in a quantum field theory. We apply this to generate several new useful scheme transformations. A comparative analysis is given of these scheme transformations in terms of their series expansion coefficients and their resultant effect on the interaction coupling, in particular at a zero of the beta function away from the origin in coupling-constant space.

We investigate gauge invariant scalar fluctuations of the metric during inflation in a nonperturbative formalism in the framework of a recently formulated scalar-tensor theory of gravity, in which the geometry of space-time is that of a Weyl integrable manifold. We show that in this scenario the Weyl scalar field can play the role of the inflaton field. As an application of the theory, we examine the case of a power-law inflation. In this case, the quasi-scale invariance of the spectrum for scalar fluctuations of the metric is achieved for determined values of the parameter $\omega$ of the scalar-tensor theory. We stress the fact that in our formalism the physical inflaton field has a purely geometrical origin.

We study how two fully featured hydrogenlike atoms harvest entanglement from the electromagnetic field vacuum, even when the atoms are spacelike separated. We compare the electromagnetic case—qualitatively and quantitatively—with previous results that used scalar fields and featureless, idealized atomic models. Our study reveals the new traits that emerge when we relax these idealizations, such as anisotropies in entanglement harvesting and the effect of exchange of angular momentum. We show that, under certain circumstances, relaxing previous idealizations makes vacuum entanglement harvesting more efficient.

The recent discovery of gravitational waves from mergers of $\sim 10M_{\odot }$ black hole binaries has stimulated interested in primordial black hole (PBH) dark matter in this mass range. Microlensing and dynamical constraints exclude all of the dark matter in compact objects with a delta function mass function in the range ${10}^{-7}\lesssim M/M_{\odot }\lesssim 10^5$. However it has been argued that all of the dark matter could be composed of compact objects in this range with an extended mass function. We explicitly recalculate the microlensing and dynamical constraints for compact objects with an extended mass function which replicates the PBH mass function produced by inflation models. We find that the microlensing and dynamical constraints place conflicting constraints on the width of the mass function, and do not find a mass function which satisfies both constraints.

We compute the stochastic gravitational wave background generated by cosmic superstrings using a semianalytical velocity-dependent model to describe their dynamics. We show that heavier string types may leave distinctive signatures on the stochastic gravitational wave background spectrum within the reach of present and upcoming gravitational wave detectors. We examine the physically motivated scenario in which the physical size of loops is determined by the gravitational backreaction scale and use NANOGrav data to derive a conservative constraint of $G{\mu }_F<3.2\times {10}^{-9}$ on the tension of fundamental strings. We demonstrate that approximating the gravitational wave spectrum generated by cosmic superstring networks using the spectrum generated by ordinary cosmic strings with reduced intercommuting probability (which is often done in the literature) leads, in general, to weaker observational constraints on $G{\mu }_F$. We show that the inclusion of heavier string types is required for a more accurate characterization of the region of the $(g_s,G{\mu }_F)$ parameter space that may be probed using direct gravitational wave detectors. In particular, we consider the observational constraints that result from NANOGrav data and show that heavier strings generate a secondary exclusion region of parameter space.

We study the polarization properties of the jitter and synchrotron radiation produced by electrons in highly turbulent anisotropic magnetic fields. The net polarization is provided by the geometry of the magnetic field the directions of which are parallel to a certain plane. Such conditions may appear in the relativistic shocks during the amplification of the magnetic field through the so-called Weibel instability. While the polarization properties of the jitter radiation allows extraction of direct information on the turbulence spectrum as well as the geometry of magnetic field, the polarization of the synchrotron radiation reflects the distribution of the magnetic field over its strength. For the isotropic distribution of monoenergetic electrons, we found that the degree of polarization of the synchrotron radiation is larger than the polarization of the jitter radiation. For the power-law energy distribution of electrons the relation between the degree of polarization of synchrotron and jitter radiation depends on the spectral index of the distribution.

We present a unified explanation for the $B$-decay anomalies in $R_{D^{(*)}}$ and $R_K$ together with the anomalous muon magnetic moment, consistent with the constraints from the current measurements of leptonic decay rates and $D^0-{\overline{D}}^0$, $B_s^0-{\overline{B}}_s^0$ mixings, within the framework of a minimal left-right symmetric gauge theory motivated by one of the low-energy subgroups of $E_6$ naturally accommodating leptoquarks.

We study the littlest Higgs model with T-parity (LHT) in the process of $pp\to W_H^{+}{W}_H^{-}\to W^{+}{W}^{-}{A}_H{A}_H$ at the 14 TeV LHC. With the $W$-jet tagging technique, we demonstrate that the bulk of the model parameter space can be probed at the level of more than $5\sigma$ in the signature of two fat $W$ jets plus large missing energy. Furthermore, we propose a novel strategy of measuring the principle parameter $f$ that is crucial to test the LHT model and to fix mass spectrum, including the dark matter particle. Our proposal can be easily incorporated into the current experimental program of diboson searches at the LHC Run-II.

We study the time evolution of the magnetic field in a plasma with a chiral magnetic current. The vector spherical harmonic (VSH) functions are used to expand all fields. We define a measure for the Chandrasekhar-Kendall-Woltjer (CKW) state, which has a simple form in VSH expansion. We propose the conditions for a general class of initial momentum spectra that will evolve into the CKW state. For this class of initial conditions, to approach the CKW state, (i) a nonvanishing chiral magnetic conductivity is necessary, and (ii) the time integration of the product of the electric resistivity and chiral magnetic conductivity must grow faster than the time integration of the resistivity. We give a few examples to test these conditions numerically, which work very well.

We derive gluon fragmentation functions in the Nambu–Jona-Lasinio (NJL) model by treating a gluon as a pair of color lines formed by a fictitious quark and antiquark ($q\overline{q}$). Gluon elementary fragmentation functions are obtained from the quark and antiquark elementary fragmentation functions for emitting specific mesons in the NJL model under the requirement that the $q\overline{q}$ pair maintains in the flavor-singlet state after meson emissions. An integral equation, which iterates the gluon elementary fragmentation functions to all orders, is then solved to yield the gluon fragmentation functions at a model scale. It is observed that these solutions are stable with respect to variation of relevant model parameters, especially after QCD evolution to a higher scale is implemented. We show that the inclusion of the gluon fragmentation functions into the theoretical predictions from only the quark fragmentation functions greatly improves the agreement with the SLD data for the pion and kaon productions in $e^{+}{e}^{-}$ annihilation. Our proposal provides a plausible construct for the gluon fragmentation functions, which are supposed to be null in the NJL model.

Higgs boson production in association with a $Z$ boson at the LHC is analyzed, both in the Standard Model and in simplified model extensions for dark matter. We focus on $H\to \text{invisibles}$ searches and show that loop-induced components for both the signal and background present phenomenologically relevant contributions to the $\mathcal{B}\mathcal{R}(H\to \text{inv})$ limits. We also show how multijet merging improves the description of key distributions to this analysis. In addition, the constraining power of this channel to simplified models for dark matter with scalar and pseudoscalar mediators $\varphi$ and $A$ is discussed and compared with noncollider constraints. We find that with $100{\mathrm{fb}}^{-1}$ of LHC data, this channel provides competitive constraints to the noncollider bounds, for most of the parameter space we consider, bounding the universal Standard Model fermion-mediator strength at $g_v<1$ for moderate masses in the range of $100\mathrm{GeV}<m_{\varphi /A}<400\mathrm{GeV}$.

We define the theoretical framework and deduce the conditions under which multimessenger astronomy can provide useful information about neutrino masses and their ordering. The framework uses time differences between the arrival of neutrinos and the other light messenger, i.e. the graviton, emitted in astrophysical catastrophes. We also provide a preliminary feasibility study elucidating the experimental reach and challenges for planned neutrino detectors such as Hyper-Kamiokande as well as future several-megaton detectors. This study shows that future experiments can be useful in independently testing the cosmological bounds on absolute neutrino masses. Concretely, the success of such measurements depends crucially on the available rate of astrophysical events and further requires development of high resolution timing besides the need for megaton-size detectors.

If a new high-mass resonance is discovered at the Large Hadron Collider, model-independent techniques to identify the production mechanism will be crucial to understand its nature and effective couplings to Standard Model particles. We present a powerful and model-independent method to infer the initial state in the production of any high-mass color-singlet system by using a tight veto on accompanying hadronic jets to divide the data into two mutually exclusive event samples (jet bins). For a resonance of several hundred GeV, the jet binning cut needed to discriminate quark and gluon initial states is in the experimentally accessible range of several tens of GeV. It also yields comparable cross sections for both bins, making this method viable already with the small event samples available shortly after a discovery. Theoretically, the method is made feasible by utilizing an effective field theory setup to compute the jet cut dependence precisely and model independently and to systematically control all sources of theoretical uncertainties in the jet binning, as well as their correlations. We use a 750 GeV scalar resonance as an example to demonstrate the viability of our method.

The phase structure and the infrared behavior of the Euclidean three-dimensional $O(2)$ symmetric ghost scalar field $\varphi$ has been investigated in Wegner and Houghton’s renormalization group framework, including higher derivatives in the kinetic term. It is pointed out that higher-derivative coupling provides three phases and leads to a triple point in that RG scheme. The types of the phase transitions have also been identified.

We have performed a complete study of self-dual configurations in a $CPT$-odd and Lorentz-violating gauged $O(3)$ nonlinear sigma model. We have consistently implemented the Bogomol’nyi-Prasad-Sommerfield (BPS) formalism and obtained the correspondent differential first-order equations describing electrically charged self-dual configurations. The total energy and magnetic flux of the vortices, besides being proportional to the winding number, also depend explicitly on the Lorentz-violating coefficients belonging to the sigma sector. The total electrical charge is proportional to the magnetic flux such as it occurs in Chern-Simons models. The Lorentz violation in the sigma sector allows one to interpolate between Lorentz-violating versions of some sigma models: the gauged $O(3)$ sigma model and the Maxwell-Chern-Simons $O(3)$ sigma model. The Lorentz violation enhances the amplitude of the magnetic field and BPS energy density near the origin, augmenting the deviation in relation to the solutions deprived of Lorentz violation.

We study the phase space for a scalar-tensor string inspired model of dark energy with nonminimal kinetic and Gauss-Bonnet couplings. The form of the scalar potential and of the coupling terms is of the exponential type, which gives rise to appealing cosmological solutions. The critical points describe a variety of cosmological scenarios that go from a matter or radiation dominated universe to a dark energy dominated universe. Trajectories were found in the phase space departing from unstable or saddle fixed points and arriving at the stable scalar field dominated point corresponding to late-time accelerated expansion.

The $\mathrm{\Lambda }(1405)$ baryon is difficult to detect in experiment, absent in many quark model calculations, and supposedly manifested through a two-pole structure. Its uncommon properties make it the subject of numerous experimental and theoretical studies, including those by the Adelaide group who report lattice-QCD eigenvalues for different quark masses. We compare these eigenvalues to predictions of a model based on Unitary Chiral Perturbation Theory. The $\mathrm{U}\chi \mathrm{PT}$ calculation predicts the quark mass dependence remarkably well. It also predicts the overlap pattern with different meson-baryon components, mainly $\pi \mathrm{\Sigma }$ and $\overline{K}N$, at different quark masses, which might help in the construction of meson-baryon operators for improved level detection on the lattice. More accurate lattice QCD data are required to draw definite conclusions on the nature of the $\mathrm{\Lambda }(1405)$.

It is demonstrated that many important features of single-pion production in $pp$ collisions at intermediate energies ($T_p\simeq 400–800\mathrm{MeV}$) can naturally be explained by supposing excitation of intermediate diproton resonances in $pp$ channels ${{}^{1}D}_2$, ${{}^{3}F}_3$ and ${{}^{3}P}_2$, in addition to conventional mechanisms involving an intermediate $\mathrm{\Delta }$-isobar. We predict for the first time the crucial role of the ${{}^{3}P}_2$ diproton resonance, found in recent experiments on the single-pion production reaction $pp\to pp({{}^{1}S}_0){\pi }^0$, in reproducing the proper behavior of spin-correlation parameters in the reaction $pp\to d{\pi }^{+}$ which were poorly described by conventional meson-exchange models to date. The possible quark structure of the $P$-wave diproton resonances is also discussed.

The magnetic susceptibility of the QCD vacuum is analyzed in the framework of a nonlocal SU(3) Polyakov–Nambu–Jona-Lasinio model. Considering two different model parametrizations, we estimate the values of the $u$- and $s$-quark tensor coefficients and magnetic susceptibilities and then we extend the analysis to finite temperature systems. Our numerical results are compared to those obtained in other theoretical approaches and in lattice QCD calculations.