Modern Physics Letters A

After the gauge invariant gluon condensation, gluons remain as massless excitations. When the effective theory describing the condensation and the excitation is constructed, a constraint has to be imposed for the vacuum to be stable. The constraint implies the perfect dia-electricity and assures the solution of color flux tube when quarks are introduced. Thus the dia-electric model of Kogut–Susskind and 't Hooft is derived by the stability of the condensed vacuum.

Does massless (λΦ⁴)₄ theory exhibit spontaneous symmetry breaking (SSB)? The raw one-loop result implies that it does, but the "RG-improved" result implies the opposite. We argue that the appropriate "low-energy effective theory" is a nonlocal field theory involving an attractive, long-range interaction Φ²(x)Φ²(y)/|x-y|⁴. RG improvement then requires running couplings for both this interaction and the original pointlike interaction. A crude calculation in this framework yields SSB even after "RG improvement" and closely agrees with the raw one-loop result.

Loop corrections induce a dependence on the momentum squared of the coefficients of the Standard Model Lagrangian, making highly nontrivial (or even impossible) the diagonalization of its quadratic part. Fortunately, the introduction of appropriate counterterms solves this puzzle.

We investigate a string theoretic cosmological model in the context of the gauged Wess–Zumino–Witten model. Our model is based on a product of non-compact coset space and a spectator flat space; [SL(2, R)/U(1)]_k × ℝ². We extend the formerly studied semiclassical consideration with infinite Kac–Moody level k to a finite one. In this case, the tachyon field appears in the effective action, and we solve the Einstein equation to determine the behavior of tachyon as a function of time. We find that tachyon field dominates over dilaton field in early times. In particular, we consider the energy conditions of the matter fields consisting of the dilaton and the tachyon which affect the initial singularity. We find that not only the strong energy but also the null energy condition is violated.

We discuss the gauge dependence of fermion mass definition under the on-shell and pole mass renormalization prescriptions. By the two-loop-level calculation of the cross section of the physical process , we prove for the first time that the on-shell fermion mass renormalization prescription makes physical result gauge-dependent. On the other hand, such gauge dependence does not appear in the result of the pole mass renormalization prescription. Our calculation also implies that the difference of physical results between the two mass renormalization prescriptions cannot be neglected at two-loop level.

In this work we study the spherical symmetric solutions of f(R) gravity in the metric formalism. We show that for a generic f(R) gravity, the spherical symmetric solution is consistent with the modified gravity equations except in the case of imposing an extra condition for the metric.

Symmetries of the string effective action describing the coupled gravity, dilaton and Kalb–Ramond fields (called EDKR theory for brevity) are studied. A previously proposed extended double-complex method is used and some double structures of the dimensionally reduced (from (2+d)-dim to 2-dim) EDKR theory are found. A 2d × 2d matrix double-complex H-potential is constructed and the field equations are extended to a double-complex formulation. Moreover, a pair of extended double-complex Hauser–Ernst-type linear systems are established, and based on these linear systems, explicit formulations of new hidden double symmetry transformations for the EDKR theory are given. These symmetry transformations constitute double infinite-dimensional Lie algebras, each of which is a semidirect product of the Kac–Moody and Virasoro algebras (without center charges). These results demonstrate that the EDKR theory under consideration possesses richer symmetry structures than previously expected.

The possible mismatch between the theoretical and experimental absorption edge peaks in semiconductors in a magnetic field background may arise due to the approximation scheme used to analytically calculate the absorption coefficient. As a possible remedy we suggest to consider nontrivial boundary conditions on x–y plane by in-equivalently quantizing the exciton in background magnetic field. This inequivalent quantization is based on von Neumann's method of self-adjoint extension, which is characterized by a parameter Σ. We obtain bound state solution and scattering state solution, which in general depend upon the self-adjoint extension parameter Σ. The parameter Σ can be used to fine tune the optical absorption coefficient K(Σ) to match with the experiment.