On the Problem of Vacuum Energy in FLRW Universes and Dark Energy

We present a (hopefully) novel calculation of the vacuum energy in expanding FLRW spacetimes based on the renormalization of quantum field theory in non-zero backgrounds. We compute the renormalized effective action up to the $2-$point function and then apply the formalism to the cosmological backgrounds of interest. As an example we calculate for quasi de Sitter spacetimes the leading correction to the vacuum energy given by the tadpole diagram and show that it behaves as $\sim H_0^2 \Lambda_{\rm pl}$ where $H_0$ is the Hubble constant and $\Lambda_{\rm pl}$ is the Planck constant. This is of the same order of magnitude as the observed dark energy density in the universe.Comment: 5 pages, 1 figure; v2: reorganization of the presentation and minor changes and comments adde

Self-Gravitating Phase Transitions: Point Particles, Black Holes and Strings

We compute the quantum string entropy S_s(m,j) of the microscopic string states of mass m and spin j in two physically relevant backgrounds: Kerr (rotating) black holes and de Sitter (dS) space-time. We find a new formula for the quantum gravitational entropy S_{sem} (M, J), as a function of the usual Bekenstein-Hawking entropy S_{sem}^(0)(M, J). We compute the quantum string emission by a black hole in de Sitter space-time (bhdS). In all these cases: (i) strings with the highest spin, and (ii) in dS space-time, (iii) quantum rotating black holes, (iv) quantum dS regime, (v) late bhdS evaporation, we find a new gravitational phase transition with a common distinctive universal feature: A square root branch point singularity in any space-time dimensions. This is the same behavior as for the thermal self-gravitating gas of point particles (de Vega-Sanchez transition), thus describing a new universality class.Comment: Invited lecture at `Statistical Mechanics of Non-Extensive Systems', Observatoire de Paris, 24-25 October 2005, to be published in a Special issue of `Les Comptes rendus de l'Academie des sciences', Elsevie

FONCTIONNEMENT ADVERBIAL ET SENS EN EMPLOI DE À UN POINT (QUE P)

RÉSUMÉ. A un point que est présenté par les dictionnaires de langue, notamment le Trésor de la Langue Française (TLFi) comme une locution adverbiale « assimilable à un adverbe de degré, d’intensité » (article Point). Il s’agit là, en fait, non pas de sa nature mais de l’un de ses emplois. En emploi adverbial, cette séquence en point présente une latitude combinatoire conforme à celle des adverbes de degré. En dépit de ce comportement adverbial, à un point que P est identifié, dans le cadre de cet article, non pas comme une locution adverbiale mais comme une locution prépositionnelle à complément zéro. D’un point de vue sémantique, elle  constitue un adverbe de degré tout comme beaucoup, très, extrêmement et énormément toutefois à un point que P véhicule un degré bien plus intense. Ce sens émane, selon nous, de l’association du sens de chacun de ses éléments constitutifs. Mots-clés: adverbe, degré, intensifieur, locution, modifieur, quantifieur, structure interne.ABSTRACT. A un point que is defined by language dictionaries, especially by the Trésor de la Langue Française (TLFi), as an adverbial locution « comparable to an adverb of degree or intensity » (Point). In fact this is not a definition of its nature but of one of its uses. In its adverbial usage, this sequence in point presents combinatorial latitude in accordance with adverbs of degree. Despite this adverbial behavior, à un point que P is not identified, within the frame of this article, with an adverbial locution but with a prepositional locution with a zero complement. It is an adverb of degree as beaucoup, très, extrêmement and énormément. Yet, à un point que P conveys a more intense degree. According to us, this meaning comes from the combination of the meaning of each constitutive element. Keywords: adverb, degree, intensifier, internal structure, locution, modifier, quantifier

L’EMPLOI EXCLAMATIF DE A QUEL POINT

 RÉSUMÉ. La locution adverbiale à quel point appartient à une sous-classe particulière d’adverbes appelés adverbes de quantité, tout comme l’adverbe combien, qui sert souvent à la gloser. Cette classification établie à partir du trait sémantique fondamental de degré, permet de présenter les propriétés générales communes aux adverbes de quantité mais non d’en saisir les particularités.  L’objectif de ce présent travail est donc d’élaborer une description minutieuse centrée sur à quel point (emploi exclamatif) afin de saisir les spécificités syntaxiques, distributionnelles et sémantiques de ce marqueur exclamatif. Pour ce faire, nous avons procédé par induction en rassemblant un corpus attesté, en français contemporain, représentatif des différents emplois exclamatifs de à quel point. L’observation des données rassemblées nous a permis, en autres, de montrer que, bien qu’appartenant à une même classe grammaticale et sémantique (adverbe indiquant le degré), à quel point et combien ont des fonctionnements syntaxiques différents et des sens en emploi fort singuliers.  Mots-clés : adverbe, conformité, degré, évaluation, intensité, quantité, seuil.ABSTRACT. It is commonly acknowledged that the adverbial locution à quel point belongs to a particular sub-class of adverbs called quantity adverbs, as the adverb combien, which serves to replace it. This classification, established from the fundamental semantic trait of degree, allows us to display its common general properties to the quantity adverbs but not to fathom its specificities. The aim of the present study is to set up a minute description centered on à quel point (in its exclamatory use) to seize the syntactic, distributional and semantic specificities relative to this marker. In order to achieve this goal, we have proceeded by induction, i.e. by gathering a certified corpus of different exclamatory uses of à quel point in contemporary French. The analysis of the gathered data has allowed us to show that, while belonging to an identical grammatical and semantic class (an adverb indicating the degree), à quel point and combien have different syntactic functioning and very particular meanings in use.Keywords: adverb, conformity, degree, evaluation, intensity, quantity, threshold

The fate of the Wilson-Fisher fixed point in non-commutative \phi^4

In this article we study non-commutative vector sigma model with the most general \phi^4 interaction on Moyal-Weyl spaces. We compute the 2- and 4-point functions to all orders in the large N limit and then apply the approximate Wilson renormalization group recursion formula to study the renormalized coupling constants of the theory. The non-commutative Wilson-Fisher fixed point interpolates between the commutative Wilson-Fisher fixed point of the Ising universality class which is found to lie at zero value of the critical coupling constant a_* of the zero dimensional reduction of the theory, and a novel strongly interacting fixed point which lies at infinite value of a_* corresponding to maximal non-commutativity beyond which the two-sheeted structure of a_* as a function of the dilation parameter disappears.Comment: 19 pages, 7 figures, v2:one reference adde

Bertotti-Robinson solutions of D=5 Einstein-Maxwell-Chern-Simons-Lambda theory

We present a series of new solutions in five-dimensional Einstein-Maxwell-Chern-Simons theory with an arbitrary Chern-Simons coupling $\gamma$ and a cosmological constant $\Lambda$. For general $\gamma$ and $\Lambda$ we give various generalizations of the Bertotti-Robinson solutions supported by electric and magnetic fluxes, some of which presumably describe the near-horizon regions of black strings or black rings. Among them there is a solution which could apply to the horizon of a topological AdS black ring in gauged minimal supergravity. Others are horizonless and geodesically complete. We also construct extremal asymptotically flat multi-string solutions for $\Lambda=0$ and arbitrary $\gamma$.Comment: 17 pages, revtex

The architectural representation, redefinition and repercussion in the era of augmented reality

Ponència presentada a: Session 4: Etnografías, fenomenología, fenomenología social y dialogía social / Ethnographies in the studios, phenomenology, social dialog

Semiclassical (Quantum Field Theory) and Quantum (String) de Sitter Regimes: New Results

We compute the quantum string entropy S_s(m, H) from the microscopic string density of states rho_s (m,H) of mass m in de Sitter space-time. We find for high m, a {\bf new} phase transition at the critical string temperature T_s= (1/2 pi k_B)L c^2/alpha', higher than the flat space (Hagedorn) temperature t_s. (L = c/H, the Hubble constant H acts at the transition as producing a smaller string constant alpha' and thus, a higher tension). T_s is the precise quantum dual of the semiclassical (QFT Hawking-Gibbons) de Sitter temperature T_sem = hbar c /(2\pi k_B L). We find a new formula for the full de Sitter entropy S_sem (H), as a function of the usual Bekenstein-Hawking entropy S_sem^(0)(H). For L << l_{Planck}, ie. for low H << c/l_Planck, S_{sem}^{(0)}(H) is the leading term, but for high H near c/l_Planck, a new phase transition operates and the whole entropy S_sem (H) is drastically different from the Bekenstein-Hawking entropy S_sem^(0)(H). We compute the string quantum emission cross section by a black hole in de Sitter (or asymptotically de Sitter) space-time (bhdS). For T_sem ~ bhdS << T_s, (early evaporation stage), it shows the QFT Hawking emission with temperature T_sem ~ bhdS, (semiclassical regime). For T_sem ~ bhdS near T_{s}, it exhibits a phase transition into a string de Sitter state of size L_s = l_s^2/L}, l_s= \sqrt{\hbar alpha'/c), and string de Sitter temperature T_s. Instead of featuring a single pole singularity in the temperature (Carlitz transition), it features a square root branch point (de Vega-Sanchez transition). New bounds on the black hole radius r_g emerge in the bhdS string regime: it can become r_g = L_s/2, or it can reach a more quantum value, r_g = 0.365 l_s.Comment: New original materia

Semiclassical (QFT) and Quantum (String) anti - de Sitter Regimes: New Results

We compute the quantum string entropy S_s(m, H) from the microscopic string density of states of mass m in Anti de Sitter space-time. For high m, (high Hm -->c/\alpha'), no phase transition occurs at the Anti de Sitter string temperature T_{s} which is higher than the flat space (Hagedorn) temperature t_{s}. (the Hubble constant H acts as producing a smaller string constant and thus, a higher tension). T_s is the precise quantum dual of the semiclassical (QFT) Anti de Sitter temperature scale . We compute the quantum string emission by a black hole in Anti de Sitter space-time (bhAdS). In the early evaporation stage, it shows the QFT Hawking emission with temperature T_{sem~bhAdS}, (semiclassical regime). For T_{sem~bhAdS}--> T_{s}, it exhibits a phase transition into a Anti de Sitter string state. New string bounds on the black hole emerge in the bhAdS string regime. We find a new formula for the full (quantum regime included) Anti de Sitter entropy S_{sem}, as a function of the usual Bekenstein-Hawking entropy S_{sem}^(0). For low H (semiclassical regime), S_{sem}^(0) is the leading term but for high H (quantum regime), no phase transition operates, in contrast to de Sitter space, and the entropy S_{sem} is very different from the Bekenstein-Hawking term S_{sem}^(0).Comment: Comments 26 pages; no figure