WZW orientifolds and finite group cohomology

The simplest orientifolds of the WZW models are obtained by gauging a Z_2 symmetry group generated by a combined involution of the target Lie group G and of the worldsheet. The action of the involution on the target is by a twisted inversion g \mapsto (\zeta g)^{-1}, where \zeta is an element of the center of G. It reverses the sign of the Kalb-Ramond torsion field H given by a bi-invariant closed 3-form on G. The action on the worldsheet reverses its orientation. An unambiguous definition of Feynman amplitudes of the orientifold theory requires a choice of a gerbe with curvature H on the target group G, together with a so-called Jandl structure introduced in hep-th/0512283. More generally, one may gauge orientifold symmetry groups \Gamma = Z_2 \ltimes Z that combine the Z_2-action described above with the target symmetry induced by a subgroup Z of the center of G. To define the orientifold theory in such a situation, one needs a gerbe on G with a Z-equivariant Jandl structure. We reduce the study of the existence of such structures and of their inequivalent choices to a problem in group-\Gamma cohomology that we solve for all simple simply-connected compact Lie groups G and all orientifold groups \Gamma = Z_2 \ltimes Z.Comment: 48+1 pages, 11 figure

Efficacy of a low-cost, inactivated whole-cell oral cholera vaccine: results from 3 years of follow-up of a randomized, controlled trial

BACKGROUND: Killed oral cholera vaccines (OCVs) have been licensed for use in developing countries, but protection conferred by licensed OCVs beyond two years of follow-up has not been demonstrated in randomized, clinical trials. METHODS/PRINCIPAL FINDINGS: We conducted a cluster-randomized, placebo-controlled trial of a two-dose regimen of a low-cost killed whole cell OCV in residents 1 year of age and older living in 3,933 clusters in Kolkata, India. The primary endpoint was culture-proven Vibrio cholerae O1 diarrhea episodes severe enough to require treatment in a health care facility. Of the 66,900 fully dosed individuals (31,932 vaccinees and 34,968 placebo recipients), 38 vaccinees and 128 placebo-recipients developed cholera during three years of follow-up (protective efficacy 66%; one-sided 95%CI lower bound = 53%, p<0.001). Vaccine protection during the third year of follow-up was 65% (one-sided 95%CI lower bound = 44%, p<0.001). Significant protection was evident in the second year of follow-up in children vaccinated at ages 1–4 years and in the third year in older age groups. CONCLUSIONS/SIGNIFICANCE: The killed whole-cell OCV conferred significant protection that was evident in the second year of follow-up in young children and was sustained for at least three years in older age groups. Continued follow-up will be important to establish the vaccine's duration of protection.Dipika Sur ... Stephen Attridge ... et al

Solitary kinetic Alfvén waves in nonextensive electron-positron-ion plasma

In low but finite β (thermal to magnetic pressure ratio) collisionless nonextensive electron-positron-ion plasma, we have derived linear dispersion relation of kinetic Alfvén waves (KAWs) and have also investigated solitary KAWs through Sagdeev pseudopotential approach in small amplitude limit. Linear analysis of KAWs shows a decrease in frequency of the wave with increase in each of the parameters, viz. r (equilibrium positron-to-ion density ratio), α (electron-to-positron temperature ratio) and q (nonextensive parameter). Nonlinear analysis of KAWs reveals that the nonextensive plasma model considered here supports only compressive solitary waves at sub-Alfvénic speeds. The effects of q, r, α and a (soliton parallel velocity) on the characteristic properties of solitary KAWs are depicted in graphical plots. The results of our present investigation may have relevance to the understanding of low-frequency electromagnetic noises/localized fluctuations in strongly magnetized electron-positron-ion plasmas having nonextensive electrons and positrons. Keywords: Kinetic Alfvén waves, Solitons, Electron-positron-ion plasma, Nonextensive statistical mechanics, q-Nonextensive distributions, Sagdeev potentia