Thermal gravity, black holes and cosmological entropy

Taking seriously the interpretation of black hole entropy as the logarithm of the number of microstates, we argue that thermal gravitons may undergo a phase transition to a kind of black hole condensate. The phase transition proceeds via nucleation of black holes at a rate governed by a saddlepoint configuration whose free energy is of order the inverse temperature in Planck units. Whether the universe remains in a low entropy state as opposed to the high entropy black hole condensate depends sensitively on its thermal history. Our results may clarify an old observation of Penrose regarding the very low entropy state of the universe.Comment: 5 pages, 2 figures, RevTex. v4: to appear in Phys. Rev.

Random graphs containing arbitrary distributions of subgraphs

Traditional random graph models of networks generate networks that are locally tree-like, meaning that all local neighborhoods take the form of trees. In this respect such models are highly unrealistic, most real networks having strongly non-tree-like neighborhoods that contain short loops, cliques, or other biconnected subgraphs. In this paper we propose and analyze a new class of random graph models that incorporates general subgraphs, allowing for non-tree-like neighborhoods while still remaining solvable for many fundamental network properties. Among other things we give solutions for the size of the giant component, the position of the phase transition at which the giant component appears, and percolation properties for both site and bond percolation on networks generated by the model.Comment: 12 pages, 6 figures, 1 tabl

The Polarization of the Cosmic Microwave Background Due to Primordial Gravitational Waves

We review current observational constraints on the polarization of the Cosmic Microwave Background (CMB), with a particular emphasis on detecting the signature of primordial gravitational waves. We present an analytic solution to the Polanarev approximation for CMB polarization produced by primordial gravitational waves. This simplifies the calculation of the curl, or B-mode power spectrum associated with gravitational waves during the epoch of cosmological inflation. We compare our analytic method to existing numerical methods and also make predictions for the sensitivity of upcoming CMB polarization observations to the inflationary gravitational wave background. We show that upcoming experiments should be able either detect the relic gravitational wave background or completely rule out whole classes of inflationary models.Comment: 25 pages, 4 figures, review published in IJMP

Constrained Dynamics of Universally Coupled Massive Spin 2-spin 0 Gravities

The 2-parameter family of massive variants of Einstein's gravity (on a Minkowski background) found by Ogievetsky and Polubarinov by excluding lower spins can also be derived using universal coupling. A Dirac-Bergmann constrained dynamics analysis seems not to have been presented for these theories, the Freund-Maheshwari-Schonberg special case, or any other massive gravity beyond the linear level treated by Marzban, Whiting and van Dam. Here the Dirac-Bergmann apparatus is applied to these theories. A few remarks are made on the question of positive energy. Being bimetric, massive gravities have a causality puzzle, but it appears soluble by the introduction and judicious use of gauge freedom.Comment: 6 pages; Talk given at QG05, Cala Gonone (Italy), September 200

Homeless shelter food production: positive implications for clients and volunteers

Within the context of a longstanding project (Behavioral Activation Project in Homeless Shelters), the Shelter Farm was developed on the grounds of a homeless shelter located in a food desert. The Behavioral Activation Project, which represents a decade-long collaboration between a Professor of Psychology at the University of Dayton (Roger N. Reeb, Ph.D.) and St. Vincent de Paul (Dayton, Ohio), fosters self-sufficiency in shelter residents as they strive to overcome personal challenges and obstacles associated with homelessness. Past research shows that the Behavioral Activation Project enhances the psychological (and adaptive) functioning of shelter residents as well as the civic-related development of service-learning students who assist in implementing the Project. In 2017, Dr. Reeb (University of Dayton) established a collaboration with Ms. Mills-Wasniak (Extension Educator, The Ohio State University Extension Montgomery County) to develop the Shelter Farm at the St. Vincent de Paul Gettysburg Gateway Shelter for Men. A Memorandum of Understanding among the three collaborative entities was developed and approved. Shelter residents volunteered to work alongside service-learning students and community partners on the farm. In the first season, we harvested nearly a ton of produce – all of which was delivered to the shelter kitchen to enhance the nutrition of shelter residents. The Shelter Farm also enhanced St. Vincent de Paul’s budget for food, as we estimated wholesale value of the produce at almost $4,000. This same level of success was replicated in Shelter Farm’s second season. As we faced COVID-19 obstacles in the third season, safety protocols were approved by all three aforementioned collaborative entities, and we sustained the Shelter Farm, harvesting approximately 1500 pounds of produce for the shelters. In the first season, a graduate student in clinical psychology at the University of Dayton completed an M.A. Thesis providing preliminary evidence that, as shelter residents volunteer to work alongside students and community partners on the farm, they show decreases in state anxiety and improvements in wellness over time. This manuscript provides the following: (a) a description of the long-standing Project that provided the infrastructure for developing the Shelter Farm, (b) a description of the collaborative process underlying the initiative, the Shelter Farm itself, and the success in sustaining the Shelter Farm, even in the face of COVID-19; (c) an overview of the benefits (nutritional and psychological) of the Shelter Farm for shelter residents; and (d) plans for sustaining and expanding the Shelter Farm (and associated research)

On the structure of the new electromagnetic conservation laws

New electromagnetic conservation laws have recently been proposed: in the absence of electromagnetic currents, the trace of the Chevreton superenergy tensor, $H_{ab}$ is divergence-free in four-dimensional (a) Einstein spacetimes for test fields, (b) Einstein-Maxwell spacetimes. Subsequently it has been pointed out, in analogy with flat spaces, that for Einstein spacetimes the trace of the Chevreton superenergy tensor $H_{ab}$ can be rearranged in the form of a generalised wave operator $\square_L$ acting on the energy momentum tensor $T_{ab}$ of the test fields, i.e., $H_{ab}=\square_LT_{ab}/2$. In this letter we show, for Einstein-Maxwell spacetimes in the full non-linear theory, that, although, the trace of the Chevreton superenergy tensor $H_{ab}$ can again be rearranged in the form of a generalised wave operator $\square_G$ acting on the electromagnetic energy momentum tensor, in this case the result is also crucially dependent on Einstein's equations; hence we argue that the divergence-free property of the tensor $H_{ab}=\square_GT_{ab}/2$ has significant independent content beyond that of the divergence-free property of $T_{ab}$

Killing tensors in pp-wave spacetimes

The formal solution of the second order Killing tensor equations for the general pp-wave spacetime is given. The Killing tensor equations are integrated fully for some specific pp-wave spacetimes. In particular, the complete solution is given for the conformally flat plane wave spacetimes and we find that irreducible Killing tensors arise for specific classes. The maximum number of independent irreducible Killing tensors admitted by a conformally flat plane wave spacetime is shown to be six. It is shown that every pp-wave spacetime that admits an homothety will admit a Killing tensor of Koutras type and, with the exception of the singular scale-invariant plane wave spacetimes, this Killing tensor is irreducible.Comment: 18 page

A weighted de Rham operator acting on arbitrary tensor fields and their local potentials

We introduce a weighted de Rham operator which acts on arbitrary tensor fields by considering their structure as r-fold forms. We can thereby define associated superpotentials for all tensor fields in all dimensions and, from any of these superpotentials, we deduce in a straightforward and natural manner the existence of 2r potentials for any tensor field, where r is its form-structure number. By specialising this result to symmetric double forms, we are able to obtain a pair of potentials for the Riemann tensor, and a single (2,3)-form potential for the Weyl tensor due to its tracelessness. This latter potential is the n-dimensional version of the double dual of the classical four dimensional (2,1)-form Lanczos potential. We also introduce a new concept of harmonic tensor fields, demonstrate that the new weighted de Rham operator has many other desirable properties and, in particular, it is the natural operator to use in the Laplace-like equation for the Riemann tensor.Comment: 33 pages: corrected typos and minor additions; reference [39] adde

Broad Down, Devon: archaeological and other stories

publication-status: PublishedThis is a post-print, author-produced version of an article accepted for publication Journal of Material Culture, 2010, Vol. 15, Issue 3, pp. 345 - 367. Copyright © 2010 SAGE Publications. The definitive publisher-authenticated version is available online at http://mcu.sagepub.com/content/15/3/345.shortThis article explores the knowledge construction process of an archaeological site in East Devon, UK. Bouncing off an oral historical account of the site that seems to run against scientific truth claims, the author investigates the story of how knowledge of the site has developed over the last two centuries. Building on previous work that explores the history and practice of archaeology, the article opens up questions of what counts as evidence. Then, taking a cue from more recent work that suggests a more dynamic and open-ended engagement with the landscape, the article turns to examine how the meaning of a site can be made and remade. As part of this endeavour, questions of what as well as who can ‘speak’ are examined and some space is opened up for the agency of ‘minor figures’, both human and non-human