The pion form factor is calculated in the framework of the charge-conjugation invariant covariant spectator theory. This formalism is established in Minkowski space, and the calculation is set up in momentum space. In a previous calculation we included only the leading pole coming from the spectator quark (referred to as the relativistic impulse approximation). In this paper we also include the contributions from the poles of the quark which interacts with the photon and average over all poles in both the upper and lower half-planes in order to preserve charge conjugation invariance (referred to as the $C$-symmetric complete impulse approximation). We find that for small pion mass these contributions are significant at all values of the four-momentum transfer $Q^2$ but, surprisingly, do not alter the shape obtained from the spectator poles alone.

The study of spontaneous breakdown of spacetime symmetries leads to the discovery of another type of Higgs mechanism operating in a chiral SU(2) model. Some of the Nambu-Goldstone vector mesons emergent from simultaneous violations of gauge and Lorentz symmetries are, in this case, absorbed by a left-handed doublet and endow one of the fermions with a right-handed state, while another part becomes emergent as photons. Accordingly, this mechanism allows a chiral fermion to acquire a mass, and it may enable the emergent theory to reproduce the electromagnetism equivalent to the QED sector in the standard theory. It is also mentioned that the “fermion-boson puzzle” known in the presence of a ’t Hooft–Polyakov monopole does not exist in our theory.

We present a model-independent, nonperturbative relation between finite-volume matrix elements and infinite-volume $\mathbf{0}\to \mathbf{2}$ and $\mathbf{1}\to \mathbf{2}$ transition amplitudes. Our result accommodates theories in which the final two-particle state is coupled to any number of other two-body channels, with all angular momentum states included. The derivation uses generic, fully relativistic field theory and is exact up to exponentially suppressed corrections in the lightest particle mass times the box size. This work distinguishes itself from previous studies by accommodating particles with any intrinsic spin. To illustrate the utility of our general result, we discuss how it can be implemented for studies of $N+\mathcal{J}\to (N\pi ,N\eta ,N{\eta }^{\prime },\mathrm{\Sigma }K,\mathrm{\Lambda }K)$ transitions, where $\mathcal{J}$ is a generic external current. The reduction of rotational symmetry, due to the cubic finite volume, manifests in this example through the mixing of S and P waves when the system has nonzero total momentum.

The influence of intense magnetic fields on the behavior of color superconducting cold quark matter is investigated using an ${\mathrm{SU}(2)}_f$ Nambu-Jona-Lasinio–type model for which a novel regulation scheme is introduced. In such a scheme the contributions which are explicitly dependent on the magnetic field turn out to be finite and, thus, do not require to be regularized. As a result of this, nonphysical oscillations that might arise in the alternative regularization schemes previously used in the literature are naturally removed. In this way, a clearer interpretation of the physical oscillations is possible. The sensitivity of our results to the model parametrization is analyzed.

By combining the color dipole model of the nucleon with the assumption that cross sections behave asymptotically as ${\ln }^2(s)$, we are able to describe the data for photon, neutrino and hadron interactions with protons at all energies; $s$ is the center-of-mass energy of the interacting particles. Specifically, we extrapolate the perturbative QCD calculations into the regime of small fractional parton momenta $x$ using a color dipole description of the proton target that guarantees an asymptotic ${\ln }^2(s)$ behavior of all cross sections. The ambiguity of introducing a parametrization associated with the dipole approximation is mitigated by the requirement that the saturation of the small-$x$ structure functions produce ${\ln }^2(s)$-behaved asymptotic cross sections, in agreement with the data. The same formalism allows us to calculate the cross section for the hadronic pair production of charm particles. The results, in particular those for the high-energy neutrino and charm cross sections, are relevant for evaluating the sensitivity as well as the background in neutrino telescopes.

We study infrared contributions to semihard parton-parton interactions by considering an effective charge whose finite infrared behavior is constrained by a dynamical mass scale. Using an eikonal QCD-based model in order to connect this semihard parton-level dynamics to the hadron-hadron scattering, we obtain predictions for the proton-proton ($pp$) and antiproton-proton ($\overline{p}p$) total cross sections, ${\sigma }_{\text{tot}}^{pp,\overline{p}p}$, and the ratios of the real to imaginary part of the forward scattering amplitude, ${\rho }^{pp,\overline{p}p}$. We discuss the theoretical aspects of this formalism and consider the phenomenological implications of a class of energy-dependent form factors in the high-energy behavior of the forward amplitude. We introduce integral dispersion relations specially tailored to relate the real and imaginary parts of eikonals with energy-dependent form factors. Our results, obtained using a group of updated sets of parton distribution functions, are consistent with the recent data from the TOTEM, AUGER, and Telescope Array experiments.

In this work, we study the semileptonic decay modes $B_s^0\to {\pi }^{+}{\pi }^{-}{\ell }^{+}{\ell }^{-}$ and $D_s^{+}\to {\pi }^{+}{\pi }^{-}{\ell }^{+}\nu$ in the kinematics region where the ${\pi }^{+}{\pi }^{-}$ system has a invariant mass in the range 0.5–1.3 GeV. These processes are valuable towards the determination of S-wave ${\pi }^{+}{\pi }^{-}$ light-cone distribution amplitudes whose normalizations are scalar form factors. We compare the results for scalar form factors predicted in unitarized chiral perturbation theory and extracted from the data on the $B_s\to J/\psi {\pi }^{+}{\pi }^{-}$. Then the $B_s\to {\pi }^{+}{\pi }^{-}$ and $D_s\to {\pi }^{+}{\pi }^{-}$ form factors are calculated in light-cone sum rules, based on which predictions for differential decay widths are made. The results are in good agreement with the experimental data on the $B_s$ and $D_s$ decays into ${\pi }^{+}{\pi }^{-}$. More accurate measurements at BEPC, LHC and KEKB in the future will be helpful to examine our formalism and constrain the input parameters more precisely.

We present the first calculation of inclusive jet production in deep-inelastic scattering with approximate next-to-next-to-leading order (aNNLO) contributions, obtained from a unified threshold resummation formalism. The leading coefficients are computed analytically. We show that the aNNLO contributions reduce the theoretical prediction for jet production in deep-inelastic scattering, improve the description of the final HERA data in particular at high photon virtuality $Q^2$ and increase the central fit value of the strong coupling constant.

We use LHC dijet data to derive constraints on neutrinoless double beta decay. Upper limits on cross sections for the production of “exotic” resonances, such as a right-handed $W$ boson or a diquark, can be converted into lower limits on the double beta decay half-life for fixed choices of other parameters. Constraints derived from run-I data are already surprisingly strong and complementary to results from searches using same-sign dileptons plus jets. For the case of the left-right symmetric model, in case no new resonance is found in future runs of the LHC and assuming $g_L=g_R$, we estimate a lower limit on the double beta decay half-life larger than ${10}^{27}$ yr can be derived from future dijet data, except in the window of relatively light right-handed neutrino masses in the range 0.5 MeV to 50 GeV. Part of this mass window will be tested in the upcoming SHiP experiment. We also discuss current and future limits on possible scalar diquark contributions to double beta decay that can be derived from dijet data.

We report a measurement of the branching fraction ratios $R(D^{(*)})$ of $\overline{B}\to D^{(*)}{\tau }^{-}{\overline{\nu }}_{\tau }$ relative to $\overline{B}\to D^{(*)}{\ell }^{-}{\overline{\nu }}_{\ell }$ (where $\ell =e$ or $\mu$) using the full Belle data sample of $772\times {10}^{6}B\overline{B}$ pairs collected at the $\mathrm{\Upsilon }(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. The measured values are $R(D)=0.375\pm 0.064(\text{stat})\pm 0.026(\text{syst})$ and $R(D^{*})=0.293\pm 0.038(\text{stat})\pm 0.015(\text{syst})$. The analysis uses hadronic reconstruction of the tag-side $B$ meson and purely leptonic $\tau$ decays. The results are consistent with earlier measurements and do not show a significant deviation from the standard model prediction.

Polarization of strange quarks is preserved to a high degree when they hadronize into $\mathrm{\Lambda }$ baryons, as observed in $Z$ decays at LEP. This opens up the possibility for ATLAS and CMS to use strange-quark polarization measurements as a characterization tool for new physics scenarios that produce such quarks. Measurements in $t\overline{t}$ samples would be useful for obtaining additional information about the polarization transfer from the strange quark to the $\mathrm{\Lambda }$ baryon. Already with $100{\mathrm{fb}}^{-1}$ in run 2, $t\overline{t}$ samples in ATLAS and CMS become competitive in sensitivity with the $Z$ samples of the LEP experiments. Moreover, while the LEP measurements were done inclusively over all quark flavors, which makes their interpretation dependent on various modeling assumptions, $t\overline{t}$ events at the LHC offer multiple handles for disentangling the different contributions experimentally. We also discuss the possibility of measuring polarizations of up and down quarks.

Birefringence is one of the fascinating properties of the vacuum of quantum electrodynamics (QED) in strong electromagnetic fields. The scattering of linearly polarized incident probe photons into a perpendicularly polarized mode provides a distinct signature of the optical activity of the quantum vacuum and thus offers an excellent opportunity for a precision test of nonlinear QED. Precision tests require accurate predictions and thus a theoretical framework that is capable of taking the detailed experimental geometry into account. We derive analytical solutions for vacuum birefringence which include the spatio-temporal field structure of a strong optical pump laser field and an x-ray probe. We show that the angular distribution of the scattered photons depends strongly on the interaction geometry and find that scattering of the perpendicularly polarized scattered photons out of the cone of the incident probe x-ray beam is the key to making the phenomenon experimentally accessible with the current generation of FEL/high-field laser facilities.

We study a ${\varphi }^4$ theory at finite temperature in a finite volume. Quantum, thermal and volume fluctuations are treated with the functional renormalization group. Specifically, we focus on the interplay of temperature and length scales driving the system. We find that thermodynamical observables at finite volume such as the pressure approach the infinite volume limit similarly to that of the vanishing temperature limit. We also advance the functional renormalization group method at finite volume. In particular, we identify requirements for suitable regulators that admit the exponential thermal and finite volume decay properties.

Until now, the first reported doubly charmed baryon ${\mathrm{\Xi }}_{cc}^{+}(3520)$ is still a puzzle. It was discovered and confirmed by SELEX collaboration, but not confirmed by LHCb, BABAR, BELLE, FOCUS, or any other collaboration. In the present paper, by employing Regge phenomenology, we first express the mass of the ground state ($L=0$) doubly charmed baryon ${\mathrm{\Omega }}_{cc}^{*+}$ as a function of masses of the well established light baryons and singly charmed baryons. Inserting the recent experimental data, the mass of ${\mathrm{\Omega }}_{cc}^{*+}$ is given to be $3809\pm 36\mathrm{MeV}$, which is independent of any unobservable parameters. Then, with the quadratic mass relations, we calculate the masses of the ground state triply charmed baryon ${\mathrm{\Omega }}_{ccc}^{++}$ and doubly charmed baryons ${\mathrm{\Xi }}_{cc}^{(*)++}$, ${\mathrm{\Xi }}_{cc}^{(*)+}$, and ${\mathrm{\Omega }}_{cc}^{+}$ [the mass of ${\mathrm{\Xi }}_{cc}^{+}$ is determined as ${3520}_{-40}^{+41}\mathrm{MeV}$, which agrees with the mass of ${\mathrm{\Xi }}_{cc}^{+}(3520)$]. The isospin splitting $M_{{\mathrm{\Xi }}_{cc}^{++}}-M_{{\mathrm{\Xi }}_{cc}^{+}}=0.4\pm 0.3\mathrm{MeV}$. After that, masses of the orbitally excited ($L=1$, 2, 3) doubly and triply charmed baryons are estimated. The results are reasonable comparing with those extracted in many other approaches. We suggest more efforts to study doubly and triply charmed baryons both theoretically and experimentally, not only for the abundance of baryon spectra, but also for numerically examining whether the linear mass relations or the quadratic mass relations are realized in nature. Our predictions are useful for the discovery of unobserved doubly and triply charmed baryon states and the $J^P$ assignment of these states.

The minimal supersymmetric standard model leads to precise predictions of the properties of the light Higgs boson degrees of freedom that depend on only a few relevant supersymmetry-breaking parameters. In particular, there is an upper bound on the mass of the lightest neutral Higgs boson, which for a supersymmetric spectrum of the order of a TeV is barely above the one of the Higgs resonance recently observed at the LHC. This bound can be raised by considering a heavier supersymmetric spectrum, relaxing the tension between theory and experiment. In a previous article, we studied the predictions for the lightest $CP$-even Higgs mass for large values of the scalar-top and heavy Higgs boson masses. In this article we perform a similar analysis, considering also the case of a $CP$-odd Higgs boson mass $m_A$ of the order of the weak scale. We perform the calculation using effective theory techniques, considering a two-Higgs doublet model and a Standard Model-like theory and resumming the large logarithmic corrections that appear at scales above and below $m_A$, respectively. We calculate the mass and couplings of the lightest $CP$-even Higgs boson and compare our results with the ones obtained by other methods.

Recently, a large degeneracy of $J=1$ mesons—that is, larger than the $SU(2{)}_L\times SU(2{)}_R\times U(1{)}_A$ symmetry of the QCD Lagrangian—has been discovered upon truncation of the near-zero modes from the valence quark propagators. It has been found that this degeneracy represents the $SU(4)$ group that includes the chiral rotations as well as the mixing of left- and right-handed quarks. This symmetry group turns out to be a symmetry of confinement in QCD. Consequently, one expects that the same symmetry should persist upon the near-zero mode removal in other hadron sectors as well. It has been shown that indeed the $J=2$ mesons follow the same symmetry pattern upon the low-lying mode elimination. Here we demonstrate the $SU(4)$ symmetry of baryons once the near-zero modes are removed from the quark propagators. We also show a degeneracy of states belonging to different irreducible representations of $SU(4)$. This implies a larger symmetry that includes $SU(4)$ as a subgroup.

Analyzing recent ALICE data on inelastic $pp$ scattering at the LHC energies, we show that charged particle distributions exhibit geometrical scaling (GS). We show also that the inelastic cross section is scaling as well and that in this case the quality of GS is better than for multiplicities. Moreover, exponent $\lambda$ characterizing the saturation scale is for the cross-section scaling compatible with the one found in deep inelastic $ep$ scattering at HERA. Next, by parametrizing charged particle distributions by the Tsallis-like formula, we find a somewhat unexpected solution that still exhibits GS, but differs from the “standard” one where the Tsallis temperature is proportional to the saturation scale.

The artificial separation of a full-theory mode into distinct collinear and soft modes in soft-collinear effective theory leads to divergent integrals over rapidity, which are not present in the full theory. Rapidity divergence introduces an additional scale into the problem, giving rise to its own renormalization group with respect to this new scale. Two contradicting claims exist in the literature concerning rapidity scale uncertainty. One camp has shown that the results of perturbative calculations depend on the precise choice of rapidity scale. The other has derived an all-order factorization formula with no dependence on rapidity scale, by using a form of analytic regulator to regulate rapidity divergences. We deliver a simple resolution to this controversy by deriving an alternative form of the all-order factorization formula with an analytic regulator that, despite being formally rapidity scale independent, reveals how rapidity scale dependence arises when it is truncated at a finite order in perturbation theory. With our results, one can continue to take advantage of the technical ease and simplicity of the analytic regulator approach while correctly taking into account rapidity scale dependence. As an application, we update our earlier study of $WW$ production with jet veto by including rapidity scale uncertainty. While the central values of the predictions are unchanged, the scale uncertainties are increased and consistency between the next-to-leading logarithm and next-to-next-to-leading logarithm calculations is improved.

Recently hints of lepton flavor nonuniversality emerged in the BABAR and LHCb experiments. In this paper we propose tests of lepton universality in ${\nu }_{\tau }$ scattering. To parametrize the new physics we adopt an effective Lagrangian approach and consider the neutrino deep inelastic scattering processes ${\nu }_{\tau }+N\to \tau +X$ and ${\nu }_{\mu }+N\to \mu +X$ where we assume the largest new physics effects are in the $\tau$ sector. We also consider an explicit leptoquark model in our calculations. In order to make comparison with the standard model and also in order to cancel out the uncertainties of the parton distribution functions, we consider the ratio of total and differential cross sections of tau-neutrino to muon-neutrino scattering. We find new physics effects that can possibly be observed at the proposed Search for Hidden Particles (SHiP) experiment at CERN.