Large N external-field quantum electrodynamics

We advocate the study of external-field quantum electrodynamics with N charged particle flavors. Our main focus is on the Heisenberg-Euler effective action for this theory in the large N limit which receives contributions from all loop orders. The contributions beyond one loop stem from one-particle reducible diagrams. We show that specifically in constant electromagnetic fields the latter are generated by the one-loop Heisenberg-Euler effective Lagrangian. Hence, in this case the large N Heisenberg-Euler effective action can be determined explicitly at any desired loop order. We demonstrate that further analytical insights are possible for electric-and magnetic-like field configurations characterized by the vanishing of one of the secular invariants of the electromagnetic field and work out the all-orders strong field limit of the theory.

The complete singlet contribution to the massless quark form factor at three loops in QCD

It is well known that the effect of top quark loop corrections in the axial part of quark form factors (FF) does not decouple in the large top mass or low energy limit due to the presence of the axial-anomaly type diagrams. The top-loop induced singlet-type contribution should be included in addition to the purely massless result for quark FFs when applied to physics in the low energy region, both for the non-decoupling mass logarithms and for an appropriate renormalization scale dependence. In this work, we have numerically computed the so-called singlet contribution to quark FFs with the exact top quark mass dependence over the full kinematic range. We discuss in detail the renormalization formulae of the individual subsets of the singlet contribution to an axial quark FF with a particular flavor, as well as the renormalization group equations that govern their individual scale dependence. Finally we have extracted the 3-loop Wilson coefficient in the low energy effective Lagrangian, renormalized in a $$ \mathrm{non}\hbox{-} \overline{\mathrm{MS}} $$ non ‐ MS ¯ scheme and constructed to encode the leading large mass approximation of our exact results for singlet quark FFs. We have also examined the accuracy of the approximation in the low energy region.

Masses and strong decays of open charm hexaquark states $$\Sigma _{c}^{(*)}{\Sigma }_{c}^{(*)}$$

Inspired by the recent discovery of the doubly charmed tetraquark state $$T_{cc}^{+}$$ T cc + by the LHCb Collaboration, we perform a systematic study of masses and strong decays of open charm hexaquark states $${\Sigma }_{c}^{(*)}\Sigma _{c}^{(*)}$$ Σ c ( ∗ ) Σ c ( ∗ ) . Taking into account heavy quark spin symmetry breaking, we predict several bound states of isospin $$I=0$$ I = 0 , $$I=1$$ I = 1 , and $$I=2$$ I = 2 in the one boson exchange model. Moreover, we adopt the effective Lagrangian approach to estimate the decay widths of $${\Sigma }_{c}^{(*)}\Sigma _{c}^{(*)} \rightarrow \Lambda _{c}\Lambda _{c}$$ Σ c ( ∗ ) Σ c ( ∗ ) → Λ c Λ c and their relevant ratios via the triangle diagram mechanism, which range from a few MeV to a few tens of MeV. We strongly recommend future experimental searches for the $${\Sigma }_{c}^{(*)}\Sigma _{c}^{(*)}$$ Σ c ( ∗ ) Σ c ( ∗ ) hexaquark states in the $$\Lambda _c\Lambda _c$$ Λ c Λ c invariant mass distributions.

Double exotic state productions in pion and kaon induced reactions

In the present work, we investigate the pion/kaon induced $$P_c/P_{cs}$$ P c / P cs productions with $$Z_c$$ Z c state off proton target with an effective Lagrangian approach. Our estimations indicate that the cross sections depend on the model parameters and beam energies, in particular, the cross sections for $$\pi p \rightarrow Z_c(3900) P_c(4312)$$ π p → Z c ( 3900 ) P c ( 4312 ) and $$\pi p \rightarrow Z_c(3900) P_c(4440)$$ π p → Z c ( 3900 ) P c ( 4440 ) are similar and can reach up to 10 nb, while those for $$\pi p \rightarrow Z_c(3900) P_c(4457)$$ π p → Z c ( 3900 ) P c ( 4457 ) can be 30 nb. As for $$Kp \rightarrow Z_{cs}(3985)P_c$$ K p → Z cs ( 3985 ) P c , the cross sections are about 2.5 times smaller than those for $$\pi p \rightarrow Z_c(3900) P_c$$ π p → Z c ( 3900 ) P c . The discussed processes in the present work, especially $$\pi p \rightarrow Z_c(3900) P_c(4457)$$ π p → Z c ( 3900 ) P c ( 4457 ) process, may be accessible by the high-energy pion and kaon beams in the facilities of J-PARC and COMPASS.

Explicit soft supersymmetry breaking in the heterotic M-theory B − L MSSM

The strongly coupled heterotic M-theory vacuum for both the observable and hidden sectors of the B − L MSSM theory is reviewed, including a discussion of the “bundle” constraints that both the observable sector SU(4) vector bundle and the hidden sector bundle induced from a single line bundle must satisfy. Gaugino condensation is then introduced within this context, and the hidden sector bundles that exhibit gaugino condensation are presented. The condensation scale is computed, singling out one line bundle whose associated condensation scale is low enough to be compatible with the energy scales available at the LHC. The corresponding region of Kähler moduli space where all bundle constraints are satisfied is presented. The generic form of the moduli dependent F-terms due to a gaugino superpotential — which spontaneously break N = 1 supersymmetry in this sector — is presented and then given explicitly for the unique line bundle associated with the low condensation scale. The moduli-dependent coefficients for each of the gaugino and scalar field soft supersymmetry breaking terms are computed leading to a low-energy effective Lagrangian for the observable sector matter fields. We then show that at a large number of points in Kähler moduli space that satisfy all “bundle” constraints, these coefficients are initial conditions for the renormalization group equations which, at low energy, lead to completely realistic physics satisfying all phenomenological constraints. Finally, we show that a substantial number of these initial points also satisfy a final constraint arising from the quadratic Higgs-Higgs conjugate soft supersymmetry breaking term.

Probing charmonium-like XYZ states in hadron–hadron ultraperipheral collisions and electron–proton scattering

Exclusive production of charmonium-like XYZ states in hadron–hadron ultraperipheral collisions (UPCs) and electron–proton scattering are studied employing the effective Lagrangian method. Total cross sections and rapidity distributions of charmonium-like XYZ states are obtained in hadron–hadron UPCs and the electron–proton scattering process. These predictions can be applied to estimate the observed event number of exclusive charmonium-like XYZ states in hadron–hadron UPCs and electron–proton scattering. The results indicate that it is significant to search X(3872) and $$Z^+_c(3900)$$ Z c + ( 3900 ) in pA UPCs, and the Electron–Ion Collider in China will be an advantageous platform to observe XYZ states in the future.

Generic one-loop matching conditions for rare meson decays

Leptonic and semileptonic meson decays that proceed via flavour-changing neutral currents provide excellent probes of physics of the standard model and beyond. We present explicit results for the Wilson coefficients of the weak effective Lagrangian for these decays in any perturbative model in which these processes proceed via one-loop contributions. We explicitly show that our results are finite and gauge independent, and provide Mathematica code that implements our results in an easily usable form.

BPS Skyrme submodels of the five-dimensional Skyrme model

In this paper, we search for the BPS skyrmions in some BPS submodels of the generalized Skyrme model in five-dimensional spacetime using the BPS Lagrangian method. We focus on the static solutions of the Bogomolny’s equations and their corresponding energies with topological charge B > 0 is an integer. We consider two main cases based on the symmetry of the effective Lagrangian of the BPS submodels, i.e. the spherically symmetric and non-spherically symmetric cases. For the spherically symmetric case, we find two BPS submodels. The first BPS submodels consist of a potential term and a term proportional to the square of the topological current. The second BPS submodels consist of only the Skyrme term. The second BPS submodel has BPS skyrmions with the same topological charge B > 1, but with different energies, that we shall call “topological degenerate” BPS skyrmions. It also has the usual BPS skyrmions with equal energies, if the topological charge is a prime number. Another interesting feature of the BPS skyrmions, with B > 1, in this BPS submodel, is that these BPS skyrmions have non-zero pressures in the angular direction. For the non-spherically symmetric case, there is only one BPS submodel, which is similar to the first BPS submodel in the spherically symmetric case. We find that the BPS skyrmions depend on a constant k and for a particular value of k we obtain the BPS skyrmions of the first BPS submodel in the spherically symmetric case. The total static energy and the topological charge of these BPS skyrmions also depend on this constant. We also show that all the results found in this paper satisfy the full field equations of motions of the corresponding BPS submodels.