Stability and causality are investigated for quantum field theories incorporating Lorentz and CPT violation. Explicit calculations in the quadratic sector of a general renormalizable Lagrangian for a massive fermion reveal that no difficulty arises for low energies if the parameters controlling the breaking are small, but for high energies either energy positivity or microcausality is violated in some observer frame. However, this can be avoided if the Lagrangian is the sub-Planck limit of a nonlocal theory with spontaneous Lorentz and CPT violation. Our analysis supports the stability and causality of the Lorentz-and CPT-violating standard-model extension that would emerge at low energies from spontaneous breaking in a realistic string theory.

Spacetime-varying coupling constants can be associated with violations of local Lorentz invariance and CPT symmetry. An analytical supergravity cosmology with a time-varying fine-structure constant provides an explicit example. Estimates are made for some experimental constraints. DOI: 10.1103/PhysRevD.68.123511 PACS number͑s͒: 98.80.Cq, 11.30.Cp, 11.30.Er Since Dirac's large-number hypothesis ͓1͔, spacetimevarying couplings have remained the subject of various theoretical and experimental studies. Such couplings are natural in many unified theories ͓2͔, and current claims of observational evidence for a time-varying electromagnetic coupling ͓3͔ have sparked a revival of this idea ͓4͔.In this work, we investigate the role of Lorentz symmetry in the subject, showing that spacetime-varying couplings can be associated with Lorentz and CPT violation ͓5͔. This result is intuitively reasonable because translation invariance is broken in a theory with spacetime-varying couplings, while translations and Lorentz transformations are intertwined in the Poincaré group. The vacuum then behaves as a spacetime-varying medium so Lorentz isotropy can be lost in local inertial frames.As an illustration, consider a spacetime-varying coupling associated with a term containing derivatives in a Lagrangian L. A simple example involving a scalar is a term Lʛ‫ץ‬ ‫ץ*‬ , which implies LʛϪ 1 2 ‫ץ‬ ‫ץ*(‬ ϩH.c.) upon integration by parts. If varies smoothly, ‫ץ‬ has a piece that behaves in a local inertial frame as a coefficient k for Lorentz and CPT violation. More generally, nonscalar fields can play a role, and the effects can arise through subsidiary conditions involving coefficients like k appearing in the equations of motion.All possible Lorentz-violating Lagrangian terms are given by the Lorentz-and CPT-violating standard-model extension ͓6͔, and many have been bounded experimentally in precision experiments with hadrons ͓7,8͔, protons and neutrons ͓9͔, electrons ͓10,11͔, photons ͓12,13͔, and muons ͓14͔. The theory contains all observer Lorentz scalars formed by combining operators and coefficients having Lorentz indices. Terms of this type arise, for example, from spontaneous Lorentz violation ͓15͔ and in realistic noncommutative field theories ͓16͔. The presence of translation violations induced by spacetime-varying couplings complicates theoretical and experimental analyses. Here, we focus on showing that spacetime-varying couplings and apparent Lorentz violation can arise naturally, even when the dynamics of the underlying theory is Lorentz invariant and involves only constant couplings.Our analysis is performed in the context of Nϭ4 supergravity in four dimensions. This theory is a limit of the N ϭ1 supergravity in 11 spacetime dimensions and hence also of M theory. It is sufficiently simple to permit analytical calculation involving the graviton, photon, dilaton, and axion fields, while retaining generic features of a more realistic fundamental theory. We show that smoothly varying couplings can naturally be obtained from a ...

The ProtoDUNE-SP detector is a single-phase liquid argon time projection chamber with an active volume of 7.2× 6.1× 7.0 m3. It is installed at the CERN Neutrino Platform in a specially-constructed beam that delivers charged pions, kaons, protons, muons and electrons with momenta in the range 0.3 GeV/c to 7 GeV/c. Beam line instrumentation provides accurate momentum measurements and particle identification. The ProtoDUNE-SP detector is a prototype for the first far detector module of the Deep Underground Neutrino Experiment, and it incorporates full-size components as designed for that module. This paper describes the beam line, the time projection chamber, the photon detectors, the cosmic-ray tagger, the signal processing and particle reconstruction. It presents the first results on ProtoDUNE-SP's performance, including noise and gain measurements, dE/dx calibration for muons, protons, pions and electrons, drift electron lifetime measurements, and photon detector noise, signal sensitivity and time resolution measurements. The measured values meet or exceed the specifications for the DUNE far detector, in several cases by large margins. ProtoDUNE-SP's successful operation starting in 2018 and its production of large samples of high-quality data demonstrate the effectiveness of the single-phase far detector design.

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Investigation at a φ-factory can shed light on several debated issues in particle physics. We discuss: i) recent theoretical development and experimental progress in kaon physics relevant for the Standard Model tests in the flavor sector, ii) the sensitivity we can reach in probing CPT and Quantum Mechanics from time evolution of entangled kaon states, iii) the interest for improving on the present measurements of non-leptonic and radiative decays of kaons and η/η′ mesons, iv) the contribution to understand the nature of light scalar mesons, and v) the opportunity to search for narrow di-lepton resonances suggested by recent models proposing a hidden dark-matter sector. We also report on the e + e − physics in the continuum with the measurements of (multi)hadronic cross sections and the study of γγ processes.

Within the classical Maxwell-Chern-Simons limit of the standard-model extension, the emission of light by uniformly moving charges is studied confirming the possibility of a Cerenkov-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.

The deep underground neutrino experiment (DUNE), a 40-kton underground liquid argon time projection chamber experiment, will be sensitive to the electron-neutrino flavor component of the burst of neutrinos expected from the next Galactic core-collapse supernova. Such an observation will bring unique insight into the astrophysics of core collapse as well as into the properties of neutrinos. The general capabilities of DUNE for neutrino detection in the relevant few- to few-tens-of-MeV neutrino energy range will be described. As an example, DUNE’s ability to constrain the $$\nu _e$$ ν e spectral parameters of the neutrino burst will be considered.

The sensitivity of the Deep Underground Neutrino Experiment (DUNE) to neutrino oscillation is determined, based on a full simulation, reconstruction, and event selection of the far detector and a full simulation and parameterized analysis of the near detector. Detailed uncertainties due to the flux prediction, neutrino interaction model, and detector effects are included. DUNE will resolve the neutrino mass ordering to a precision of 5$$\sigma $$ σ , for all $$\delta _{\mathrm{CP}}$$ δ CP values, after 2 years of running with the nominal detector design and beam configuration. It has the potential to observe charge-parity violation in the neutrino sector to a precision of 3$$\sigma $$ σ (5$$\sigma $$ σ ) after an exposure of 5 (10) years, for 50% of all $$\delta _{\mathrm{CP}}$$ δ CP values. It will also make precise measurements of other parameters governing long-baseline neutrino oscillation, and after an exposure of 15 years will achieve a similar sensitivity to $$\sin ^{2} 2\theta _{13}$$ sin 2 2 θ 13 to current reactor experiments.