Fundamental Gravity and Gravitational Waves

While being as old as general relativity itself, the gravitational two-body problem has never been under so intense investigation as it is today, spurred by both phenomenological and theoretical motivations. The observations of gravitational waves emitted by compact binary coalescences bear the imprint of the source dynamics, and as the sensitivity of detectors improve over years, more accurate modeling is being required. The analytic modeling of classical gravitational dynamics has been enriched in this century by powerful methods borrowed from field theory. Despite being originally developed in the context of fundamental particle quantum scatterings, their applications to classical, bound system problems have shown that many features usually associated with quantum field theory, such as, e.g., divergences and counterterms, renormalization group, loop expansion, and Feynman diagrams, have only to do with field theory, be it quantum or classical. The aim of this work is to present an overview of this approach, which models massive astrophysical objects as nonrelativistic particles and their gravitational interactions via classical field theory, being well aware that while the introductory material in the present article is meant to represent a solid background for newcomers in the field, the results reviewed here will soon become obsolete, as this field is undergoing rapid development.

Smc3 acetylation, Pds5 and Scc2 control the translocase activity that establishes cohesin dependent chromatin loops

ABSTRACTChromosome spatial organization and dynamics influence DNA-related metabolic processes. SMC complexes like cohesin are essential instruments of chromosome folding. Cohesin-dependent chromatin loops bring together distal loci to regulate gene transcription, DNA repair and V(D)J recombination processes. Here we characterize further the roles of members of the cohesin holocomplex in regulating chromatin loop expansion, showing that Scc2, which stimulates cohesin ATPase activity, is essential for the translocation process required to extend DNA loop length. Eco1-dependent acetylation of Smc3 during S phase counteracts this activity through the stabilization of Pds5, to finely tune loop sizes and stability during G2. Inhibiting Pds5 in G2 leads to a strong enlargement of pre-established, stable DNA loops, in a Scc2-dependent manner. Altogether, the study strongly supports a Scc2-mediated translocation process driving expansion of DNA loops in living cells.

Perturbation theory

This chapter provides a general description of perturbation theory in terms of Feynman diagrams. The general prescriptions of constructing Feynman diagrams in momentum space are given, including for an S-matrix. The connected Green functions and the corresponding generation functional are defined with full proofs. After introducing effective action, the chapter addresses loop expansion. The chapter ends with a discussion of Feynman diagrams in fermionic theory.

A three-dimensional velocity of an erupting prominence prior to a coronal mass ejection

We present a detailed three-dimensional (3D) view of a prominence eruption, coronal loop expansion, and coronal mass ejections (CMEs) associated with an M4.4 flare that occurred on 2011 March 8 in the active region NOAA 11165. Full-disk Hα images of the flare and filament ejection were successfully obtained by the Flare Monitoring Telescope (FMT) following its relocation to Ica University, Peru. Multiwavelength observation around the Hα line enabled us to derive the 3D velocity field of the Hα prominence eruption. Features in extreme ultraviolet were also obtained by the Atmospheric Imager Assembly onboard the Solar Dynamic Observatory and the Extreme Ultraviolet Imager on board the Solar Terrestrial Relations Observatory - Ahead satellite. We found that, following collision of the erupted filament with the coronal magnetic field, some coronal loops began to expand, leading to the growth of a clear CME. We also discuss the succeeding activities of CME driven by multiple interactions between the expanding loops and the surrounding coronal magnetic field.

On the S-matrix of Liouville theory

The S-matrix for each chiral sector of Liouville theory on a cylinder is computed from the loop expansion of correlation functions of a one-dimensional field theory on a circle with a non-local kinetic energy and an exponential potential. This action is the Legendre transform of the generating function of semiclassical scattering amplitudes. It is derived from the relation between asymptotic in- and out-fields. Its relevance for the quantum scattering process is demonstrated by comparing explicit loop diagrams computed from this action with other methods of computing the S-matrix, which are also developed.

Cohesin regulates homology search during recombinational DNA repair

SummaryHomologous recombination (HR) is a ubiquitous DNA double-strand break (DSB) repair mechanism that promotes cell survival. It entails a potentially genome-wide homology search step, carried out along a conserved RecA/Rad51-ssDNA nucleoprotein filament (NPF) assembled on each DSB ends1–3. This search is subdued to NPF-dsDNA collision probability, dictated in part by chromatin conformation2,4. In contrast to the extensive knowledge about chromatin composition and mobility changes elicited by the DNA damage checkpoint (DDC)5–7, whether, how, and to which extent a DSB impacts spatial chromatin organization, and whether this organization in turns influences the homology search process, remains ill-defined8,9. Here we characterize two layers of spatial chromatin reorganization following DSB formation inS. cerevisiae.While cohesin folds chromosomes into cohesive arrays of 10-20 kb long chromatin loops as cells arrest in G2/M10,11, the DSB-flanking regions locally interact in a resection- and 9-1-1 clamp-dependent manner, independently of cohesin and HR proteins. This local structure blocks cohesin progression, constraining the extending NPF at loop base. Functionally this organization promotes side-specificcisDSB-dsDNA interactions that scales with loop expansion span, and provides a kinetic advantage for identification of intra- over inter-chromosomal homologies. We propose that cohesins regulate homology search by promotingcisdsDNA over-sampling, both upon loop expansion-coupled unidimensional dsDNA scanning, NPF trapping, and chromosome individualization, largely independent of their role in sister chromatid cohesion.