CPT Violation, Strings, and Neutral-Meson Systems

This talk provides a short overview of recent results on possible CPT violation and some associated experimental signatures.Comment: Presented at Orbis Scientiae, January 199

Gravitational physics with antimatter

The production of low-energy antimatter provides unique opportunities to search for new physics in an unexplored regime. Testing gravitational interactions with antimatter is one such opportunity. Here a scenario based on Lorentz and CPT violation in the Standard- Model Extension is considered in which anomalous gravitational effects in antimatter could arise.Comment: 5 pages, presented at the International Conference on Exotic Atoms (EXA 2008) and the 9th International Conference on Low Energy Antiproton Physics (LEAP 2008), Vienna, Austria, September 200

The Grow-Shrink strategy for learning Markov network structures constrained by context-specific independences

Markov networks are models for compactly representing complex probability distributions. They are composed by a structure and a set of numerical weights. The structure qualitatively describes independences in the distribution, which can be exploited to factorize the distribution into a set of compact functions. A key application for learning structures from data is to automatically discover knowledge. In practice, structure learning algorithms focused on "knowledge discovery" present a limitation: they use a coarse-grained representation of the structure. As a result, this representation cannot describe context-specific independences. Very recently, an algorithm called CSPC was designed to overcome this limitation, but it has a high computational complexity. This work tries to mitigate this downside presenting CSGS, an algorithm that uses the Grow-Shrink strategy for reducing unnecessary computations. On an empirical evaluation, the structures learned by CSGS achieve competitive accuracies and lower computational complexity with respect to those obtained by CSPC.Comment: 12 pages, and 8 figures. This works was presented in IBERAMIA 201

CPT and Lorentz-invariance violation

The largest gap in our understanding of nature at the fundamental level is perhaps a unified description of gravity and quantum theory. Although there are currently a variety of theoretical approaches to this question, experimental research in this field is inhibited by the expected Planck-scale suppression of quantum-gravity effects. However, the breakdown of spacetime symmetries has recently been identified as a promising signal in this context: a number of models for underlying physics can accommodate minuscule Lorentz and CPT violation, and such effects are amenable to ultrahigh-precision tests. This presentation will give an overview of the subject. Topics such as motivations, the SME test framework, mechanisms for relativity breakdown, and experimental tests will be reviewed. Emphasis is given to observations involving antimatter.Comment: 6 page

SYM, Chern-Simons, Wess-Zumino Couplings and their higher derivative corrections in IIA Superstring theory

We find the entire form of the amplitude of two fermion strings (with different chirality), a massless scalar field and one closed string Ramond-Ramond (RR) in IIA superstring theory which is different from its IIB one. We make use of a very particular gauge fixing and explore several new couplings in IIA. All infinite $u$- channel scalar poles and $t,s$- channel fermion poles are also constructed. We find new form of higher derivative corrections to two fermion two scalar couplings and show that the first simple $(s+t+u)-$ channel scalar pole for $p+2=n$ case can be obtained by having new higher derivative corrections to SYM couplings at third order of $\alpha'$. We find that the general structure and the coefficients of higher derivative corrections to two fermion two scalar couplings are completely different from the derived $\alpha'$ higher derivative corrections of type IIB.Comment: 29 pages, no figure,Latex file,published version in EPJ

Ciprofloxacin reduces the stimulation of prostaglandin E2 output by interleukin-1 in human tendon-derived cells

Fluoroquinolone antibiotics such as ciprofloxacin can induce tendon pathology and have various effects on tendon-derived cells in culture. We are investigating whether ciprofloxacin modifies signalling responses in tendon cells. Human Achilles tendon-derived cells were preincubated with or without ciprofloxacin (50?µg/ml) and were then challenged with interleukin-1ß (IL-1ß, 1?ng/ml) for up to 48?h. Prostaglandin E2 (PGE2) output was assayed by ELISA. The expression of cyclooxygenase-2 (COX-2) was examined by Western blotting. IL-1ß stimulated a substantial and prolonged increase in the output of PGE2. Preincubation with ciprofloxacin reduced IL-1ß-induced PGE2 output at all times tested; the reduction at 48?h was 69% (99% confidence interval 59–79%; 15 experiments). Norfloxacin and ofloxacin also reduced PGE2 output. However, ciprofloxacin did not affect the induction of COX-2 by IL-1ß, measured at 4 or 48?h. Ciprofloxacin reduces IL-1ß-induced PGE2 output in tendon-derived cells. The reduction in PGE2 output could modulate various cellular activities of IL-1ß, and may be implicated in fluoroquinolone-induced tendinopathy

Isotopic variation of parity violation in atomic ytterbium

We report on measurements of atomic parity violation, made on a chain of ytterbium isotopes with mass numbers A=170, 172, 174, and 176. In the experiment, we optically excite the 6s2 1S0 -> 5d6s 3D1 transition in a region of crossed electric and magnetic fields, and observe the interference between the Stark- and weak-interaction-induced transition amplitudes, by making field reversals that change the handedness of the coordinate system. This allows us to determine the ratio of the weak-interaction-induced electric-dipole (E1) transition moment and the Stark-induced E1 moment. Our measurements, which are at the 0.5% level of accuracy for three of the four isotopes measured, allow a definitive observation of the isotopic variation of the weak-interaction effects in an atom, which is found to be consistent with the prediction of the Standard Model. In addition, our measurements provide information about an additional Z' boson.Comment: 19 pages, 4 figures, 2 table

The effect of grain size on the twin initiation stress in a TWIP steel

The influence of grain size on the twinning stress of an Fe-15Mn-2Al-2Si-0.7C Twinning Induced Plasticity (TWIP) steel has been investigated. Five grain sizes were obtained using a combination of cold rolling and annealing. Electron backscatter diffraction (EBSD) analysis revealed that the material exhibited a typical cold rolled and annealed texture. Tensile testing showed the yield stress to increase with decreasing grain size, however, the ductility of the material was not substantially affected by a reduction in grain size. Cyclic tensile testing at sub-yield stresses indicated the accumulation of plastic strain with each cycle, consequently the nucleation stress for twinning was determined. The twin stress was found to increase with decreasing grain size. Furthermore, the amount of strain accumulated was greater in the coarser grain material. It is believed that this is due to a difference in the twin thickness, which is influenced by the initial grain size of the material. SEM and TEM analysis of the material deformed to 5% strain revealed thinner primary twins in the fine grain material compared to the coarse grain. TEM examination also showed the dislocation arrangement is affected by the grain size. Furthermore, a larger fraction of stacking faults was observed in the coarse-grained material. It is concluded that the twin nucleation stress and also the thickness of the deformation twins in a TWIP steel, is influenced by the initial grain size of the material. In addition grain refinement results in a boost in strength and energy absorption capabilities in the material

Supersymmetric QCD: Exact Results and Strong Coupling

We revisit two longstanding puzzles in supersymmetric gauge theories. The first concerns the question of the holomorphy of the coupling, and related to this the possible definition of an exact (NSVZ) beta function. The second concerns instantons in pure gluodynamics, which appear to give sensible, exact results for certain correlation functions, which nonetheless differ from those obtained using systematic weak coupling expansions. For the first question, we extend an earlier proposal of Arkani-Hamed and Murayama, showing that if their regulated action is written suitably, the holomorphy of the couplings is manifest, and it is easy to determine the renormalization scheme for which the NSVZ formula holds. This scheme, however, is seen to be one of an infinite class of schemes, each leading to an exact beta function; the NSVZ scheme, while simple, is not selected by any compelling physical consideration. For the second question, we explain why the instanton computation in the pure supersymmetric gauge theory is not reliable, even at short distances. The semiclassical expansion about the instanton is purely formal; if infrared divergences appear, they spoil arguments based on holomorphy. We demonstrate that infrared divergences do not occur in the perturbation expansion about the instanton, but explain that there is no reason to think this captures all contributions from the sector with unit topological charge. That one expects additional contributions is illustrated by dilute gas corrections. These are infrared divergent, and so difficult to define, but if non-zero give order one, holomorphic, corrections to the leading result. Exploiting an earlier analysis of Davies et al, we demonstrate that in the theory compactified on a circle of radius beta, due to infrared effects, finite contributions indeed arise which are not visible in the formal limit that beta goes to infinity.Comment: 28 pages, two references added, one typo correcte

Higher Loop Spin Field Correlators in D=4 Superstring Theory

We develop calculational tools to determine higher loop superstring correlators involving massless fermionic and spin fields in four space time dimensions. These correlation functions are basic ingredients for the calculation of loop amplitudes involving both bosons and fermions in D=4 heterotic and superstring theories. To obtain the full amplitudes in Lorentz covariant form the loop correlators of fermionic and spin fields have to be expressed in terms of SO(1,3) tensors. This is one of the main achievements in this work.Comment: 59 pages, 1 figure; v2: final version published in JHE