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Georgy C.,Ecole Normale Superieure de Lyon
Astronomy and Astrophysics | Year: 2012

Context. The increasing number of observed supernova events allows for finding the progenitor star even more frequently in archive images. In a few cases, the progenitor star is a yellow supergiant star. The estimated position in the Hertzsprung-Russell diagram of these stars is not compatible with the theoretical tracks of classical single-star models. Aims. According to several authors, the mass-loss rates during the red supergiant phase could be underestimated. We study the impact of an increase in these mass-loss rates on the position of 12 to 15 M ⊙ stars at the end of their nuclear lives, in order to reconcile the theoretical tracks with the observed yellow supergiant progenitors. Methods. We have performed calculations of 12 to 15 M ⊙ rotating stellar models using the Geneva stellar evolution code. To account for the uncertainties in the mass-loss rates during the RSG phase, we increased the mass-loss rate of the star (between 3 and 10 times the standard one) during that phase and compared the evolution of stars undergoing such high mass-loss rates with models computed with the standard mass-loss prescription. Results. We show that the final position of the models in the Hertzsprung-Russell diagram depends on the mass loss they undergo during the red supergiant phase. With an increased mass-loss rate, we find that some models end their nuclear life at positions that are compatible with the observed position of several supernova progenitors. We conclude that an increased mass-loss rate (whose physical mechanism still needs to be clarified) allows single-star models to simultaneously reproduce the estimated position in the HRD of the YSG SN progenitors, as well as the SN type. © 2012 ESO. Source


Rosa A.,International School for Advanced Studies | Everaers R.,Ecole Normale Superieure de Lyon
Physical Review Letters | Year: 2014

The conformational statistics of ring polymers in melts or dense solutions is strongly affected by their quenched microscopic topological state. The effect is particularly strong for nonconcatenated unknotted rings, which are known to crumple and segregate and which have been implicated as models for the generic behavior of interphase chromosomes. Here we use a computationally efficient multiscale approach to show that melts of rings of total contour length Lr can be quantitatively mapped onto melts of interacting lattice trees with gyration radii âŸ̈Rg2(Lr)⟩â̂ Lr2ν and ν=0.32±0.01. © 2014 American Physical Society. Source


Hohm O.,Arnold Sommerfeld Center for Theoretical Physics | Samtleben H.,Ecole Normale Superieure de Lyon
Physical Review Letters | Year: 2013

Eleven-dimensional supergravity reveals large exceptional symmetries upon reduction, in accordance with the U-duality groups of M theory, but their higher-dimensional geometric origin has remained a mystery. In this Letter, we show that D=11 supergravity can be extended to be fully covariant under the exceptional groups En(n), n=6, 7, 8. Motivated by a similar formulation of double field theory we introduce an extended "exceptional spacetime." We illustrate the construction by giving the explicit E 6(6) covariant form: the full D=11 supergravity, in a 5+6 splitting of coordinates but without truncation, embeds into an E6(6) covariant 5+27 dimensional theory. We argue that this covariant form likewise comprises type IIB supergravity. © 2013 American Physical Society. Source


Hohm O.,Massachusetts Institute of Technology | Samtleben H.,Ecole Normale Superieure de Lyon
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We develop exceptional field theory for E8(8), defined on a (3+248)-dimensional generalized spacetime with extended coordinates in the adjoint representation of E8(8). The fields transform under E8(8) generalized diffeomorphisms and are subject to covariant section constraints. The bosonic fields include an "internal" dreibein and an E8(8)-valued "zweihundertachtundvierzigbein" (248-bein). Crucially, the theory also features gauge vectors for the E8(8) E bracket governing the generalized diffeomorphism algebra and covariantly constrained gauge vectors for a separate but constrained E8(8) gauge symmetry. The complete bosonic theory, with a novel Chern-Simons term for the gauge vectors, is uniquely determined by gauge invariance under internal and external generalized diffeomorphisms. The theory consistently comprises components of the dual graviton encoded in the 248-bein. Upon picking particular solutions of the constraints the theory reduces to D=11 or type IIB supergravity, for which the dual graviton becomes pure gauge. This resolves the dual graviton problem, as we discuss in detail. © 2014 American Physical Society. Source


Hohm O.,Massachusetts Institute of Technology | Samtleben H.,Ecole Normale Superieure de Lyon
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We present the details of the recently constructed E6(6)-covariant extension of 11-dimensional supergravity. This theory requires a 5+27-dimensional spacetime in which the "internal" coordinates transform in the 27̄ of E6(6). All fields are E6(6) tensors and transform under (gauged) internal generalized diffeomorphisms. The "Kaluza- Klein" vector field acts as a gauge field for the E6(6)-covariant "E-bracket" rather than a Lie bracket, requiring the presence of 2-forms akin to the tensor hierarchy of gauged supergravity. We construct the complete and unique action that is gauge invariant under generalized diffeomorphisms in the internal and external coordinates. The theory is subject to covariant section constraints on the derivatives, implying that only a subset of the extra 27 coordinates is physical. We give two solutions of the section constraints: the first preserves GL(6) and embeds the action of the complete (i.e. untruncated) 11-dimensional supergravity; the second preserves GL(5)×SL(2) and embeds complete type IIB supergravity. As a byproduct, we thus obtain an off-shell action for type IIB supergravity. © 2014 American Physical Society. Source

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