Lorentzviolating

Lorentz-violating refers to the idea that Lorentz invariance—the symmetry of physical laws under boosts and rotations, central to special relativity and embedded in the Standard Model—might not be exact. In many theories that extend or modify fundamental physics, a preferred direction or frame in spacetime can arise, leading to observable deviations from standard relativistic behavior. The concept is often explored in the context of quantum gravity, string theory, and other beyond-Standard-Model frameworks.

There are two broad ways Lorentz symmetry can be violated. Explicit Lorentz violation occurs when fixed, non-dynamical background tensors or fields enter the equations of motion, intrinsically picking out preferred directions. Spontaneous Lorentz violation happens when dynamical fields acquire nonzero vacuum expectation values, breaking symmetry in the vacuum while keeping the underlying theory consistent. Spontaneous breaking is generally considered more compatible with gravity and gauge structures in many models.

A common framework to study Lorentz violation is the Standard-Model Extension (SME), an effective-field-theory approach that adds all possible Lorentz-violating terms to the Standard Model and General Relativity, each multiplied by coefficients that can be experimentally bounded. The SME provides a systematic way to organize potential effects across sectors such as photons, fermions, and gravitons.

Consequences of Lorentz violation can include modified dispersion relations, anisotropic or energy-dependent particle speeds, altered reaction thresholds, and birefringence of light over long distances. Experimental tests span astrophysical observations (polarization and time-of-flight measurements of distant sources), high-energy cosmic rays, neutrino experiments, atomic clocks, resonant cavities, and gravitational-wave analyses. To date, no definitive evidence has been found, but stringent bounds constrain possible violations to very small levels, typically suppressed by high-energy scales near the Planck scale.