Effective Lagrangian at Cubic Order in Electromagnetic Fields and Vacuum Birefringence

Most general cubic-order Horndeski Lagrangian allowing for scaling solutions and the application to dark energy

In cubic-order Horndeski theories where a scalar field $ϕ$ is coupled to nonrelativistic matter with a field-dependent coupling $Q(ϕ)$, we derive the most general Lagrangian having scaling solutions on the isotropic and homogenous cosmological background. For constant $Q$ including the case of vanishing coupling, the corresponding Lagrangian reduces to the form $L=Xg_2(Y)-g_3(Y)\square ϕ$, where $X=-\partial_μϕ\partial^μϕ/2$ and $g_2, g_3$ are arbitrary functions of $Y=Xe^{λϕ}$ with constant $λ$. We obtain the fixed points of the scaling Lagrangian for constant $Q$ and show that the $ϕ$-matter…

闵可夫斯基背景中不可约高自旋场的协变拉格朗日三次相互作用顶点

Covariant Lagrangian Cubic Interaction Vertices For Irreducible Higher Spin Fields in Minkowski Backgrounds

本文利用 BRST 与 BRST-BV 方法构造闵可夫斯基空间中不可约高自旋场的协变三次相互作用顶点，并证明完整与不完全 BRST 算子所得拉格朗日动力学的等价性可提升，同时给出 Q_c 方法下约束需构成阿贝尔超代数的条件。

Axion-induced birefringence effects in laser driven nonlinear vacuum interaction

The propagation of a probe electromagnetic field through a counterpropagating strong plane wave is investigated. The effects of the electromagnetic field-(pseudo)scalar axion field interaction and of the self-interaction of the electromagnetic field mediated by virtual electron-positron pairs in the effective Lagrangian approach are included. First, we show that if the strong field is circularly polarized, contrary to the leading-order nonlinear QED effects, the axion-photon interaction induces a chiral-like birefringence and a dichroism in the vacuum. The latter effect is explained by evoking…

Crystalline Color Superconductivity: Effective Lagrangian and Phonon Dispersion Law

The recent study by Bowers and Rajagopal on the possible structures for the QCD crystalline color superconducting phase favors a cubic structure and allows for a first discussion of the QCD dynamics in the crystalline phase. The cubic structure leads to complete breaking of traslation invariance and to three phonon modes. We discuss the expected form of the effective Lagrangian and the phonon dispersion laws assuming the proposed crystal structure. Besides the interest for QCD and the related possible relevance to compact stars these considerations may become useful to atomic systems exhibitin…

Vacuum Magnetic Birefringence Experiment as a probe of Dark Sector

Vacuum magnetic birefringence (VMB) is a nonlinear electromagnetic effect predicted by QED. In addition to the effect from QED, the effect also has a possibility to probe the dark sector. The effect predicted by QED is parity conservative, but the effect from the dark sector can induce parity violation. To pursue this possibility, we calculated the effect from the dark sector with the generalized Heisenberg-Euler effective Lagrangian that is applicable to parity-violating theories. Various dark sector models exist, among which the contribution of the dark sector neutrinos to the VMB experiment…

Propagation of field disturbances in the Yang-Mills theory

The propagation of field disturbances is examined in the context of the effective Yang-Mills Lagrangian, which is intended to be applied to QCD systems. It is shown that birefringence phenomena can occur in such systems provided some restrictive conditions, as causality, are fulfilled. Possible applications to phenomenology are addressed.

Cubic Ideal Ferromagnets at Low Temperature and Weak Magnetic Field

The low-temperature series for the free energy density, pressure, magnetization and susceptibility of cubic ideal ferromagnets in weak external magnetic fields are discussed within the effective Lagrangian framework up to three loops. The structure of the simple, body-centered, and face-centered cubic lattice is taken into account explicitly. The expansion involves integer and half-integer powers of the temperature. The corresponding coefficients depend on the magnetic field and on low-energy effective constants that can be expressed in terms of microscopic quantities. Our formulas may also se…

Laser-driven search of axion-like particles including vacuum polarization effects

Oscillations of photons into axion-like particles in a high-intensity laser field are investigated. Nonlinear QED effects are considered through the low energy behavior of the vacuum polarization tensor, which is derived from the Euler-Heisenberg Lagrangian in the one-loop and weak field approximations. The expressions obtained in this framework are applied to the configuration in which the strong background field is a circularly polarized monochromatic plane wave. The outcomes of this analysis reveal that, in the regime of low energy-momentum transfer, the axion field induces a chiral-like bi…

Phonons and gluons in the crystalline color superconducting phase of QCD

The High Density Effective Theory formalism is used to calculate the low energy properties of the phonons and gluons in the Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase of two-flavor QCD. The effective phonon Lagrangian for the cubic crystal structure, which is favored according to a recent study, depends, at the second order in the derivatives, on three parameters which we calculate in this paper. We also compute for soft momenta the effective lagrangian for the gluons of the unbroken SU(2)_c group, both for a single plane wave structure and for the cube. In both cases the Meissner gluon mas…

在 SU(5) 中调谐至深渊边缘

Tuning to the Edge of the Abyss in SU(5)

本文提出一种机制，通过将无量纲参数调谐至正定性域边界并利用Lagrangian三次项驱动对称性破缺，使得在低尺度参数的SU(5)模型中产生远高于经典尺度的GUT尺度，挑战了QFT作为有效场论的传统观点。

Dark Energy and Modified Gravity in Degenerate Higher-Order Scalar-Tensor (DHOST) theories: a review

This article reviews scalar-tensor theories characterized by a Lagrangian that, despite the presence of second order derivatives, contain a single scalar degree of freedom. These theories, known as Degenerate Higher-Order Scalar-Tensor (DHOST) theories, include Horndeski and Beyond Horndeski theories. They propagate a single scalar mode as a consequence of the degeneracy of their Lagrangian and, therefore, are not plagued by an Ostrodradsky instability. They have been fully classified up to cubic order in second-order derivatives. The study of their phenomenological consequences restricts the …

Constraints on massive vector dark energy models from integrated Sachs-Wolfe-galaxy cross-correlations

The gravitational-wave event GW170817, together with the electromagnetic counterpart, shows that the speed of tensor perturbations $c_T$ on the cosmological background is very close to that of light $c$ for the redshift $z<0.009$. In generalized Proca theories, the Lagrangians compatible with the condition $c_T=c$ are constrained to be derivative interactions up to cubic order, besides those corresponding to intrinsic vector modes. We place observational constraints on a dark energy model in cubic-order generalized Proca theories with intrinsic vector modes by running the Markov chain Monte Ca…