arXiv subjects

Ralf Lehnert

Publications and source records attributed to Ralf Lehnert.

At least 55 records · Page 3Linked to original sources

arXiv2006

CPT- and Lorentz-symmetry breaking: a review

The breakdown of spacetime symmetries has recently been identified as a promising candidate signal for underlying physics, possibly arising through quantum-gravitational effects. This talk gives an overview over various aspects of CPT- and Lorentz-violation research. Particular emphasis is given to the interplay between CPT, Lorentz, and translation symmetry, mechanisms for CPT and Lorentz breaking, and the construction of a low-energy quantum-field description of such effect. This quantum field framework, called the SME, is employed to determine possible phenomenological consequences of CPT and Lorentz violation for neutral-meson interferometry.

hep-ph↗

arXiv2006

Spacetime symmetries of the Lorentz-violating Maxwell-Chern-Simons model

The spacetime symmetries of classical electrodynamics supplemented with a Chern-Simons term that contains a constant nondynamical 4-vector are investigated. In addition to translation invariance and the expected three remaining Lorentz symmetries characterized by the little group of the external vector, the model possesses an additional spacetime symmetry if the nondynamical vector is lightlike. The conserved current associated with this invariance is determined, and the symmetry structure arising from this invariance and the usual little group ISO(2) is identified as SIM(2).

hep-th↗

arXiv2006

Non-local on-shell field redefinition for the SME

This work instigates a study of non-local field mappings within the Lorentz- and CPT-violating Standard-Model Extension (SME). An example of such a mapping is constructed explicitly, and the conditions for the existence of its inverse are investigated. It is demonstrated that the associated field redefinition can remove b-type Lorentz violation from free SME fermions in certain situations. These results are employed to obtain explicit expressions for the corresponding Lorentz-breaking momentum-space eigenspinors and their orthogonality relations.

hep-th↗

arXiv2006

Aspects of spacetime-symmetry violations

The violation of spacetime symmetries provides a promising candidate signal for underlying physics, possibly arising at the Planck scale. This talk gives an overview over various aspects in the field, including some mechanisms for Lorentz breakdown, the SME test framework, and phenomenological signatures for such effects.

gr-qc↗

arXiv2006

Lorentz and CPT tests involving antiprotons

Lorentz and CPT tests involving matter-antimatter comparisons at low temperatures are discussed. SME predictions for transition frequencies in such systems include both matter-antimatter differences and sidereal variations. In hydrogen-antihydrogen spectroscopy, leading-order effects in a 1S-2S transition as well as in a 1S Zeeman transition could exist that can be employed to obtain clean constraints. Similarly, tight bounds can be determined from Penning-trap experiments involving antiprotons.

hep-ph↗

arXiv2005

Cosmology and spacetime symmetries

Cosmological models often contain scalar fields, which can acquire global nonzero expectation values that change with the comoving time. Among the possible consequences of these scalar-field backgrounds, an accelerated cosmological expansion, varying couplings, and spacetime-symmetry violations have recently received considerable attention. This talk studies the interplay of these three key signatures of cosmologically varying scalars within a supergravity framework.

hep-ph↗

arXiv2005

Spacetime symmetries and varying scalars

This talk discusses the relation between spacetime-dependent scalars, such as couplings or fields, and the violation of Lorentz symmetry. A specific cosmological supergravity model demonstrates how scalar fields can acquire time-dependent expectation values. Within this cosmological background, excitations of these scalars are governed by a Lorentz-breaking dispersion relation. The model also contains couplings of the scalars to the electrodynamics sector leading to the time dependence of both the fine-structure parameter alpha and the theta angle. Through these couplings, the variation of the scalars is also associated with Lorentz- and CPT-violating effects in electromagnetism.

gr-qc↗

arXiv2005

Lorentz violation as a quantum-gravity signature

Many theoretical approaches to quantum gravity predict the breakdown of Lorentz symmetry at Planck energies. Kinematical cosmic-ray studies are a sensitive tool in the search for such effects. This talk discusses the construction of test dispersion relations for such analyses.

astro-ph↗

arXiv2004

The Cherenkov effect in Lorentz-violating vacua

The emission of electromagnetic radiation by charges moving uniformly in a Lorentz-violating vacuum is studied. The analysis is performed within the classical Maxwell-Chern-Simons limit of the Standard-Model Extension (SME) and confirms the possibility of a Cherenkov-type effect. In this context, various properties of Cherenkov radiation including the rate, polarization, and propagation features, are discussed, and the back-reaction on the charge is investigated. An interpretation of this effect supplementing the conventional one is given. The emerging physical picture leads to a universal methodology for studying the Cherenkov effect in more general situations.

hep-ph↗

arXiv2004

Vacuum Cherenkov radiation

Within the classical Maxwell-Chern-Simons limit of the Standard-Model Extension (SME), the emission of light by uniformly moving charges is studied confirming the possibility of a Cherenkov-type effect. In this context, the exact radiation rate for charged magnetic point dipoles is determined and found in agreement with a phase-space estimate under certain assumptions.

hep-ph↗

arXiv2004

Lorentz-violating dispersion relations and threshold analyses

Remnant low-energy effects of Planck-scale Lorentz breaking in candidate fundamental theories typically include modified one-particle dispersion relations. Theoretical constraints on such modifications are discussed leading to the exclusion of a variety of previously considered Lorentz-violating parameters. In particular, the fundamental principle of coordinate independence, the role of an effective dynamical framework, and the conditions of positivity and causality are investigated.

hep-ph↗

arXiv2004

The Lorentz-violating Standard-Model Extension

Quantum-gravity effects are expected to be suppressed by the Planck mass. For experimental progress it is therefore important to identify potential signatures from Planck-scale physics that are amenable to ultrahigh-precision tests. It is argued that minuscule violations of Lorentz and CPT symmetry are candidate signals. In addition, theoretical and experimental aspects of the Standard-Model Extension, which describes the emergent low-energy effects, are discussed.

hep-ph↗

arXiv2004

Dirac theory within the Standard-Model Extension

The modified Dirac equation in the Lorentz-violating Standard-Model Extension (SME) is considered. Within this framework, the construction of a hermitian Hamiltonian to all orders in the Lorentz-breaking parameters is investigated, discrete symmetries and the first-order roots of the dispersion relation are determined, and various properties of the eigenspinors are discussed.

hep-ph↗

arXiv2003

Fundamental physics and Lorentz violation

The violation of Lorentz symmetry can arise in a variety of approaches to fundamental physics. For the description of the associated low-energy effects, a dynamical framework known as the Standard-Model Extension has been developed. This talk gives a brief review of the topic focusing on Lorentz violation through varying couplings.

hep-ph↗

arXiv2003

Couplings varying on cosmological scales and Lorentz breaking

In the context of N=4 supergravity in four dimensions, we present an exact classical solution that leads to spacetime-dependent electromagnetic couplings and discuss the ensuing Lorentz-violating effects. We comment briefly on experimental bounds.

hep-ph↗

arXiv2003

Cosmological acceleration, varying couplings, and Lorentz breaking

Many candidate fundamental theories contain scalar fields that can acquire spacetime-varying expectation values in a cosmological context. Such scalars typically obey Lorentz-violating effective dispersion relations. We illustrate this fact within a simple supergravity model that also exhibits the observed late-time cosmological acceleration and implies varying electromagnetic couplings.

astro-ph↗

arXiv2003

Apparent Lorentz violation through spacetime-varying couplings

In this talk, we explore the relation between smoothly varying couplings and Lorentz violation. Within the context of a supergravity model, we present an explicit mechanism that causes the effective fine-structure parameter and the effective electromagnetic $θ$ angle to acquire related spacetime dependences. We argue that this leads to potentially observable Lorentz violation and discuss some implications for the Standard-Model Extension.

hep-ph↗

arXiv2003

Threshold analyses and Lorentz violation

In the context of threshold investigations of Lorentz violation, we discuss the fundamental principle of coordinate invariance, the role of an effective dynamical framework, and the conditions of positivity and causality. Our analysis excludes a variety of previously considered Lorentz-breaking parameters and opens an avenue for viable dispersion-relation investigations of Lorentz violation.

gr-qc↗