5,254 research outputs found
Measurements of CPT Violation at LHCb
Recent measurements of CPT violation and Lorentz symmetry breaking in
mixing and mixing, obtained from data taken
by the LHCb experiment, are highlighted. The results are expressed in terms of
the Standard-Model Extension (SME) coefficients, which incorporate both CPT and
Lorentz violation. Due to the large boost of the mesons at LHCb, the SME
coefficients can be determined with high precision. The bounds on these
coefficients are improved significantly compared to previous measurements.Comment: Presented at the Seventh Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, June 20-24, 201
FDA Regulation of Electronic Nicotine Delivery Systems and the âDeemingâ Rule: Whatâs Left for States?
Search for ultralight scalar dark matter with atomic spectroscopy
We report new limits on ultralight scalar dark matter (DM) with dilaton-like
couplings to photons that can induce oscillations in the fine-structure
constant alpha. Atomic dysprosium exhibits an electronic structure with two
nearly degenerate levels whose energy splitting is sensitive to changes in
alpha. Spectroscopy data for two isotopes of dysprosium over a two-year span is
analyzed for coherent oscillations with angular frequencies below 1 rad/s. No
signal consistent with a DM coupling is identified, leading to new constraints
on dilaton-like photon couplings over a wide mass range. Under the assumption
that the scalar field comprises all of the DM, our limits on the coupling
exceed those from equivalence-principle tests by up to 4 orders of magnitude
for masses below 3 * 10^-18 eV. Excess oscillatory power, inconsistent with
fine-structure variation, is detected in a control channel, and is likely due
to a systematic effect. Our atomic spectroscopy limits on DM are the first of
their kind, and leave substantial room for improvement with state-of-the-art
atomic clocks.Comment: 5 pages, 4 figures; v2: references adde
Reactive Turing Machines
We propose reactive Turing machines (RTMs), extending classical Turing
machines with a process-theoretical notion of interaction, and use it to define
a notion of executable transition system. We show that every computable
transition system with a bounded branching degree is simulated modulo
divergence-preserving branching bisimilarity by an RTM, and that every
effective transition system is simulated modulo the variant of branching
bisimilarity that does not require divergence preservation. We conclude from
these results that the parallel composition of (communicating) RTMs can be
simulated by a single RTM. We prove that there exist universal RTMs modulo
branching bisimilarity, but these essentially employ divergence to be able to
simulate an RTM of arbitrary branching degree. We also prove that modulo
divergence-preserving branching bisimilarity there are RTMs that are universal
up to their own branching degree. Finally, we establish a correspondence
between executability and finite definability in a simple process calculus
- âŠ