EFT beyond the horizon: stochastic inflation and how primordial quantum fluctuations go classical

We identify the effective theory describing inflationary super-Hubble scales and show it to be a special case of effective field theories appropriate to open systems. Open systems allow information to be exchanged between the degrees of freedom of interest and those that are integrated out, such as for particles moving through a fluid. Strictly speaking they cannot in general be described by an effective lagrangian; rather the appropriate `low-energy' limit is instead a Lindblad equation describing the evolution of the density matrix of the slow degrees of freedom. We derive the equation relevant to super-Hubble modes of quantum fields in near-de Sitter spacetimes and derive two implications. We show the evolution of the diagonal density-matrix elements quickly approaches the Fokker-Planck equation of Starobinsky's stochastic inflationary picture. This provides an alternative first-principles derivation of this picture's stochastic noise and drift, as well as its leading corrections. (An application computes the noise for systems with a sub-luminal sound speed.) We argue that the presence of interactions drives the off-diagonal density-matrix elements to zero in the field basis. This shows why the field basis is the `pointer basis' for the decoherence of primordial quantum fluctuations while they are outside the horizon, thus allowing them to re-enter as classical fluctuations, as assumed when analyzing CMB data. The decoherence process is efficient, occurring after several Hubble times even for interactions as weak as gravitational-strength. Crucially, the details of the interactions largely control only the decoherence time and not the nature of the final late-time stochastic state, much as interactions can control the equilibration time for thermal systems but are largely irrelevant to the properties of the resulting equilibrium state

On the Strength of First Order Phase Transitions

Electroweak baryogenesis may solve one of the most fundamental questions we can ask about the universe, that of the origin of matter. It has become clear in the past few years that it also poses a multi-faceted challenge. In order to compute the tiny primordial baryonic excess, we probably must invoke physics beyond the standard model (an exciting prospect for most people), we must push perturbation theory to its ``limits'' (or beyond), and we must deal with nonequilibrium aspects of the phase transition. In this talk, I focus mainly on the latter issue, that of nonequilibrium aspects of first order transitions. In particular, I discuss the elusive question of ``weakness''. What does it mean to have a weak first order transition, and how can we distinguish between weak and strong? I argue that weak and strong transitions have very different dynamics; while strong transitions proceed by the usual bubble nucleation mechanism, weak transitions are characterized by a mixing of phases as the system reaches the critical temperature from above. I show that it is possible to clearly distinguish between the two, and discuss consequences for studies of first order transitions in general. (Invited talk given at the ``Electroweak Physics and the Early Universe'' workshop, Sintra, March 23-25, 1994.)Comment: 16 pages, 4 figures not included (can be obtained from hep-ph/9403310, or by request) RevTeX, DART-HEP-94/0

Brane-World Gravity

The observable universe could be a 1+3-surface (the "brane") embedded in a 1+3+\textit{d}-dimensional spacetime (the "bulk"), with Standard Model particles and fields trapped on the brane while gravity is free to access the bulk. At least one of the \textit{d} extra spatial dimensions could be very large relative to the Planck scale, which lowers the fundamental gravity scale, possibly even down to the electroweak ($\sim$ TeV) level. This revolutionary picture arises in the framework of recent developments in M theory. The 1+10-dimensional M theory encompasses the known 1+9-dimensional superstring theories, and is widely considered to be a promising potential route to quantum gravity. At low energies, gravity is localized at the brane and general relativity is recovered, but at high energies gravity "leaks" into the bulk, behaving in a truly higher-dimensional way. This introduces significant changes to gravitational dynamics and perturbations, with interesting and potentially testable implications for high-energy astrophysics, black holes, and cosmology. Brane-world models offer a phenomenological way to test some of the novel predictions and corrections to general relativity that are implied by M theory. This review analyzes the geometry, dynamics and perturbations of simple brane-world models for cosmology and astrophysics, mainly focusing on warped 5-dimensional brane-worlds based on the Randall--Sundrum models. We also cover the simplest brane-world models in which 4-dimensional gravity on the brane is modified at \emph{low} energies -- the 5-dimensional Dvali--Gabadadze--Porrati models. Then we discuss co-dimension two branes in 6-dimensional models.Comment: A major update of Living Reviews in Relativity 7:7 (2004) "Brane-World Gravity", 119 pages, 28 figures, the update contains new material on RS perturbations, including full numerical solutions of gravitational waves and scalar perturbations, on DGP models, and also on 6D models. A published version in Living Reviews in Relativit

Estrogen- and Progesterone (P4)-Mediated Epigenetic Modifications of Endometrial Stromal Cells (EnSCs) and/or Mesenchymal Stem/Stromal Cells (MSCs) in the Etiopathogenesis of Endometriosis

Endometriosis is a common chronic inflammatory condition in which endometrial tissue appears outside the uterine cavity. Because ectopic endometriosis cells express both estrogen and progesterone (P4) receptors, they grow and undergo cyclic proliferation and breakdown similar to the endometrium. This debilitating gynecological disease affects up to 15% of reproductive aged women. Despite many years of research, the etiopathogenesis of endometrial lesions remains unclear. Retrograde transport of the viable menstrual endometrial cells with retained ability for attachment within the pelvic cavity, proliferation, differentiation and subsequent invasion into the surrounding tissue constitutes the rationale for widely accepted implantation theory. Accordingly, the most abundant cells in the endometrium are endometrial stromal cells (EnSCs). These cells constitute a particular population with clonogenic activity that resembles properties of mesenchymal stem/stromal cells (MSCs). Thus, a significant role of stem cell-based dysfunction in formation of the initial endometrial lesions is suspected. There is increasing evidence that the role of epigenetic mechanisms and processes in endometriosis have been underestimated. The importance of excess estrogen exposure and P4 resistance in epigenetic homeostasis failure in the endometrial/endometriotic tissue are crucial. Epigenetic alterations regarding transcription factors of estrogen and P4 signaling pathways in MSCs are robust in endometriotic tissue. Thus, perspectives for the future may include MSCs and EnSCs as the targets of epigenetic therapies in the prevention and treatment of endometriosis. Here, we reviewed the current known changes in the epigenetic background of EnSCs and MSCs due to estrogen/P4 imbalances in the context of etiopathogenesis of endometriosis

Agriculture – Who Cares? An Investigation of ‘Care Farming’ in the UK

‘Care farming’ (variously ‘green care in agriculture’, ‘farming for health’, ‘social farming’ and ‘therapeutic agriculture’) in the UK has grown rapidly over the last five years from the low base identified by preliminary scoping studies conducted at that time. In countries where the activity is most widely practised, the research focus has been primarily upon the care provided by farms, leaving a paucity of knowledge about the farms providing care. However, such care is ‘co-produced’, meaning that insights from both agricultural geography and the geographies of care deserve to be unified. In the British context, an agricultural perspective has seldom been applied; where done so, it has dismissed care farming as merely ‘hobby farming’ or conceptualised it as a minor economic activity helping to diversify the farm business and illustrating ‘multifunctionality’. Surprisingly little attention has been paid to either its relationship with productive ‘core’ farming activities or the consequences for farmers themselves. Using questionnaires and interviews, the express purpose of this paper is to identify and explicate the characteristics of care farms and farmers. Analysis reveals that it is not easy to pigeon-hole care farmers according to their age, motives, size of farm or land tenure. The paper moves on to discuss the transformative nature of care farming on the way in which farmers live their lives. In particular, symbiotic humaneanimal relations emerge regardless of whether livestock are kept as pets or commercial enterprises. Also revealed is the altruistic satisfaction of farmers as they provide ethical care and see positive changes in their service users. The paper concludes by suggesting how the multiple connections that are found to result from the interaction of agricultural practises and care provision might be more accurately conceptualised and articulated as 'connective' agriculture