A Novel Approach to the Cosmological Constant Problem

We propose a novel infinite-volume brane world scenario where we live on a non-inflating spherical 3-brane, whose radius is somewhat larger than the present Hubble size, embedded in higher dimensional bulk. Once we include higher curvature terms in the bulk, we find completely smooth solutions with the property that the 3-brane world-volume is non-inflating for a continuous range of positive values of the brane tension, that is, without fine-tuning. In particular, our solution, which is a near-BPS background with supersymmetry broken on the brane around TeV, is controlled by a single integration constant.Comment: 20 pages, revte

Scalar Field with Robin Boundary Conditions in the Worldline Formalism

The worldline formalism has been widely used to compute physical quantities in quantum field theory. However, applications of this formalism to quantum fields in the presence of boundaries have been studied only recently. In this article we show how to compute in the worldline approach the heat kernel expansion for a scalar field with boundary conditions of Robin type. In order to describe how this mechanism works, we compute the contributions due to the boundary conditions to the coefficients A_1, A_{3/2} and A_2 of the heat kernel expansion of a scalar field on the positive real line.Comment: Presented at 8th Workshop on Quantum Field Theory Under the Influence of External Conditions (QFEXT 07), Leipzig, Germany, 16-21 Sep 200

Automated Analysis of MUTEX Algorithms with FASE

In this paper we study the liveness of several MUTEX solutions by representing them as processes in PAFAS s, a CCS-like process algebra with a specific operator for modelling non-blocking reading behaviours. Verification is carried out using the tool FASE, exploiting a correspondence between violations of the liveness property and a special kind of cycles (called catastrophic cycles) in some transition system. We also compare our approach with others in the literature. The aim of this paper is twofold: on the one hand, we want to demonstrate the applicability of FASE to some concrete, meaningful examples; on the other hand, we want to study the impact of introducing non-blocking behaviours in modelling concurrent systems.Comment: In Proceedings GandALF 2011, arXiv:1106.081

A Remark on Smoothing Out Higher Codimension Branes

We discuss some issues arising in studying (linearized) gravity on non-BPS higher codimension branes in an infinite-volume bulk. In particular, such backgrounds are badly singular for codimension-3 and higher delta-function-like branes with non-zero tension. As we discuss in this note, non-trivial issues arise in smoothing out such singularities. Thus, adding higher curvature terms might be necessary in this context.Comment: 8 pages, revtex, a minor misprint corrected (to appear in Mod. Phys. Lett. A

Microscopic mechanism of protein cryopreservation in an aqueous solution with trehalose

In order to investigate the cryoprotective mechanism of trehalose on proteins, we use molecular dynamics computer simulations to study the microscopic dynamics of water upon cooling in an aqueous solution of lysozyme and trehalose. We find that the presence of trehalose causes global retardation of the dynamics of water. Comparing aqueous solutions of lysozyme with/without trehalose, we observe that the dynamics of water in the hydration layers close to the protein is dramatically slower when trehalose is present in the system. We also analyze the structure of water and trehalose around the lysozyme and find that the trehalose molecules form a cage surrounding the protein that contains very slow water molecules. We conclude that the transient cage of trehalose molecules that entraps and slows the water molecules prevents the crystallisation of protein hydration water upon cooling.DC, EGS, and HES thank the NSF chemistry Division for support (Grants CHE-1213217, CHE-0911389, and CHE-0908218). PG gratefully acknowledges the computational support reveived by the INFN RM3-GRID at Roma Tre University. (CHE-1213217 - NSF chemistry Division; CHE-0911389 - NSF chemistry Division; CHE-0908218 - NSF chemistry Division)Published versio

Geografia e televisione: dagli spazi locali agli spazi globali

Il rapporto tra geografia e televisione \ue8 un campo di studio ancora troppo poco esplorato. La comunicazione televisiva ha portato alla globalizzazione dei mercati e delle idee e, contemporaneamente, ha rafforzato le culture locali. La domanda \ue8 allora, per i geografi, se la televisione pu\uf2 aiutare ad abbattere le frontiere o se, al contrario, contribuisce a rafforzare i confini determinati da vincoli di identit\ue0 culturale. The relationship between Geography and Television is a field of study still too little explored. The television communication has led to the globalization of markets and of ideas and, simultaneously, has reinforced local cultures The question is then, to geographers, if television can help to tear down the borders or whether, on the contrary, contributes to strengthen the boundaries affected by ties of cultural identity

The conodont apparatus of Zieglerodina eladioi (Valenzuela Rios, 1994)

Zieglerodina eladioi (Valenzuela-Ríos) è una specie di conodonti ozarkodinidi documentata dalla parte più alta del Přídolí (Siluriano superiore) al Lochkoviano medio (Devoniano Inferiore). La specie è stata istituita nei Pirenei spagnoli e fino a ora è documentata in diverse aree del nord Gondwana (Marocco, Alpi Carniche, Sardegna, Repubblica Ceca e Turchia). L’apparato di Zieglerodina eladioi viene ricostruito basandosi su ritrovamenti in Marocco, Sardegna e nelle Alpi Carniche; esso comprende sei elementi (P1, P2, M, S0, S1 e S2) in cui gli elementi ramiformi sono caratterizzati da una denticolazione alternata con denticoli aghiformi. La morfologia dell’apparato conferma l’attribuzione della specie al genere Zieglerodina.Zieglerodina eladioi (Valenzuela-Ríos) is a small ozarkodinid from the latest Přídolí (Silurian) and the Lochkovian (Lower Devonian), up to now documented only in areas of North Gondwana. Material from Morocco, the Carnic Alps, and Sardinia provide the basis for the seximembrate reconstruction of this conodont species’ apparatus (consisting of P1, P2, M, S0, S1, and S2 elements). The ramiform elements of Zieglerodina eladioi are characterised by an alternate denticulation with spike-like denticles, further confirming the attribution of the species to the genus Zieglerodina

Dressed Dirac propagator from a locally supersymmetric N=1 spinning particle

We study the Dirac propagator dressed by an arbitrary number N of photons by means of a worldline approach, which makes use of a supersymmetric N=1 spinning particle model on the line, coupled to an external Abelian vector field. We obtain a compact off-shell master formula for the tree level scattering amplitudes associated to the dressed Dirac propagator. In particular, unlike in other approaches, we express the particle fermionic degrees of freedom using a coherent state basis, and consider the gauging of the supersymmetry, which ultimately amounts to integrating over a worldline gravitino modulus, other than the usual worldline einbein modulus which corresponds to the Schwinger time integral. The path integral over the gravitino reproduces the numerator of the dressed Dirac propagator

Blown-up p-Branes and the Cosmological Constant

We consider a blown-up 3-brane, with the resulting geometry R^(3,1) \times S^(N-1), in an infinite-volume bulk with N > 2 extra dimensions. The action on the brane includes both an Einstein term and a cosmological constant. Similar setups have been proposed both to reproduce 4-d gravity on the brane, and to solve the cosmological constant problem. Here we obtain a singularity-free solution to Einstein's equations everywhere in the bulk and on the brane, which allows us to address these question explicitely. One finds, however, that the proper volume of S^(N-1) and the cosmological constant on the brane have to be fine-tuned relatively to each other, thus the cosmological constant problem is not solved. Moreover the scalar propagator on the brane behaves 4-dimensionally over a phenomenologically acceptable range only if the warp factor on the brane is huge, which aggravates the Weak Scale - Planck Scale hierarchy problem.Comment: 21 pages, no figure