A calculation of the Weyl anomaly for 6D Conformal Higher Spins

In this work we continue the study of the one-loop partition function for higher derivative conformal higher spin (CHS) fields in six dimensions and its holographic counterpart given by massless higher spin Fronsdal fields in seven dimensions. In going beyond the conformal class of the boundary round 6-sphere, we start by considering a Ricci-flat, but not conformally flat, boundary and the corresponding Poincar\'e-Einstein spacefilling metric. Here we are able to match the UV logarithmic divergence of the boundary with the IR logarithmic divergence of the bulk, very much like in the known 4D/5D setting, under the assumptions of factorization of the higher derivative CHS kinetic operator and WKB-exactness of the heat kernel of the dual bulk field. A key technical ingredient in this construction is the determination of the fourth heat kernel coefficient b6 for Lichnerowicz Laplacians on both 6D and 7D Einstein manifolds. These results allow to obtain, in addition to the already known type-A Weyl anomaly, two of the three independent type-B anomaly coefficients in terms of the third, say c_3 for instance. In order to gain access to c_3, and thus determine the four central charges independently, we further consider a generic non Ricci-flat Einstein boundary. However, in this case we find a mismatch between boundary and bulk computations for spins higher than two. We close by discussing the nature of this discrepancy and perspectives for a possible amendment.Comment: 13 page

Clasificación de los revoques multiestratificados del claustro de S. Abbondio en Como (Italia): un instrumento analítico para la arqueología de la arquitectura

S. Abbondio (Como, Italia) es una de las mas extraordinariasbasilicas romanicas presentes en el norte de Italia.El edificio entero y en particular el claustro ha sido expuestoa varias intervenciones durante los ultimos siglos, enparticular los ultimos trabajos de conservacion ejecutadosentre los anos 2000 y 2003. En esta ocasion se ha efectuadouna vasta campana diagnostica sobre los revoquestanto internos como externos, destinada a clasificarlosdesde el punto de vista compositivo-morfologico y paradescubrir la historia sobre la conservacion del claustro.Revoques representativos de las diferentes fases constructivashan sido identificados con la utilizacion de metodoscomo el analisis de difraccion de rayos X en polvo,porosimetria por intrusion de mercurio, microscopia opticapara secciones finas y espectrometria atomica. Losresultados han permitido agrupar las muestras que presentabancaracteristicas similares, confirmando hipotesishistoricas sobre la secuencia de las intervenciones en eledificio, sugiriendo un metodo analitico que podria serusado como un instrumento valido en caso de estudiossobre la arqueologia de la arquitectura

One-loop divergences in 7D Einstein and 6D conformal gravities

Indexación: ScopusThe aim of this note is to unveil a striking equivalence between the one-loop divergences in 7D Einstein and 6D Conformal Gravities. The particular combination of 6D pointwise Weyl invariants of the 6D Conformal Gravity corresponds to that of Branson’s Q-curvature and can be written solely in terms of the Ricci tensor and its covariant derivatives. The quadratic metric fluctuations of this action, 6D Weyl graviton, are endowed with a sixth-order kinetic operator that happens to factorize on a 6D Einstein background into product of three shifted Lichnerowicz Laplacians. We exploit this feature to use standard heat kernel techniques and work out in one go the UV logarithmic divergences of the theory that contains in this case the four Weyl anomaly coefficients. In a seemingly unrelated computation, we determine the one-loop IR logarithmic divergences of 7D Einstein Gravity in a particular 7D Poincaré-Einstein background that is asymptotically hyperbolic and has the above 6D Einstein manifold at its conformal infinity or boundary. We show the full equivalence of both computations, as an outgrowth of the IR/UV connection in AdS/CFT correspondence, and in this way the time-honoured one-loop calculations in Einstein and higher-derivative gravities take an interesting new turn. © 2020, The Author(s)

Excitonic and lattice contributions to the charge density wave in 1T-TiSe2 revealed by a phonon bottleneck

Understanding collective electronic states such as superconductivity and charge density waves is pivotal for fundamental science and applications. The layered transition metal dichalcogenide 1T-TiSe2 hosts a unique charge density wave (CDW) phase transition whose origins are still not fully understood. Here, we present ultrafast time- and angle-resolved photoemission spectroscopy (TR-ARPES) measurements complemented by time-resolved reflectivity (TRR) which allows us to establish the contribution of excitonic and electron-phonon interactions to the CDW. We monitor the energy shift of the valence band (VB) and coupling to coherent phonons as a function of laser fluence. The VB shift, directly related to the CDW gap closure, exhibits a markedly slower recovery dynamics at fluences above Fth = 60 microJ cm-2. This observation coincides with a shift in the relative weight of coherently coupled phonons to higher frequency modes in time-resolved reflectivity (TRR), suggesting a phonon bottleneck. Using a rate equation model, the emergence of a high-fluence bottleneck is attributed to an abrupt reduction in coupled phonon damping and an increase in exciton dissociation rate linked to the loss of CDW superlattice phonons. Thus, our work establishes the important role of both excitonic and phononic interactions in the CDW phase transition and the advantage of combining complementary femtosecond techniques to understand the complex interactions in quantum materials.Comment: 11 pages, 4 figure

Integrated approach to the characterisation of historical mortars: the case study of St. Lorenzo Basil in Milan

This work deals with an integrated approach to the characterisation of historical mortars. Various techniques (Optical Microscopy on thin sections, X-Ray Diffraction, FTIR Spectroscopy, Thermal Analyses, Ionic Chromatography) were utilised in order to thoroughly analyse the mortars coming from the Basilica of St. Lorenzo (Milan, Italy), on occasion of a recent conservation work. Investigations from various, complementary points of view allowed the identification of the original components of the mortars, i. e. binder and aggregate fraction, besides the nature of degradation compounds, in order to plan the best and most respectful intervention