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Bervillier C.,CNRS Laboratory for Theoretical Physics
Nuclear Physics B

The conventional absence of field renormalization in the local potential approximation (LPA) - implying a zero value of the critical exponent η - is shown to be incompatible with the logic of the derivative expansion of the exact renormalization group (RG) equation. We present a LPA with η ≠ 0 that strictly does not make reference to any momentum dependence. Emphasis is made on the perfect breaking of the reparametrization invariance in that pure LPA (absence of any vestige of invariance) which is compatible with the observation of a progressive smooth restoration of that invariance on implementing the two first orders of the derivative expansion whereas the conventional requirement (η = 0 in the LPA) precluded that observation. © 2013 Elsevier B.V. Source

Bervillier C.,CNRS Laboratory for Theoretical Physics
Condensed Matter Physics

The non-linear way the anomalous dimension parameter has been introduced in the historic first version of the exact renormalization group equation is compared to current practice. A simple expression for the exactly marginal redundant operator proceeds from this non-linearity, whereas in the linear case, first order differential equations must be solved to get it. The role of this operator in the construction of the flow equation is highlighted. © C. Bervillier, 2013. Source

Solodukhin S.N.,CNRS Laboratory for Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology

We discuss the renormalization of the Newton constant due to fields of various spin s. We first briefly review the cases of s=0,1/2,1,3/2 already discussed in the literature and notice the appearance of the well-known contact terms for the vector bosons. We then extend this discussion of the contact terms to massive vector fields, p-forms and to the case of spin s=2 particles (gravitons). We observe that, in general, the contact terms originate from the fields which mediate the interactions (such as vector gauge bosons and gravitons). We then discuss entanglement entropy and the conical entropy and their relation to the renormalized Newton constant. We address the puzzle of the nonanalytic terms due to fields of spin s=2 and suggest that the resolution of this puzzle comes from the nonequivalence of the orbifold and n-fold cover constructions which are used in the entropy calculations. Finally, we propose a mechanism by which the Bekenstein-Hawking entropy is identified with entanglement entropy in any theory which includes both matter fields and the mediators of interactions (vector gauge bosons and gravitons). © 2015 American Physical Society. Source

Damour T.,Institute des Hautes etudes Scientifiques | Nagar A.,Institute des Hautes etudes Scientifiques | Villain L.,CNRS Laboratory for Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology

The gravitational wave signal from a binary neutron star inspiral contains information on the nuclear equation of state. This information is contained in a combination of the tidal polarizability parameters of the two neutron stars and is clearest in the late inspiral, just before merger. We use the recently defined tidal extension of the effective one-body formalism to construct a controlled analytical description of the frequency-domain phasing of neutron star inspirals up to merger. Exploiting this analytical description we find that the tidal polarizability parameters of neutron stars can be measured by the advanced LIGO-Virgo detector network from gravitational wave signals having a reasonable signal-to-noise ratio of ρ=16. This measurability result seems to hold for all the nuclear equations of state leading to a maximum mass larger than 1.97M. We also propose a promising new way of extracting information on the nuclear equation of state from a coherent analysis of an ensemble of gravitational wave observations of separate binary merger events. © 2012 American Physical Society. Source

Poilblanc D.,CNRS Laboratory for Theoretical Physics | Misguich G.,CEA Saclay Nuclear Research Center
Physical Review B - Condensed Matter and Materials Physics

The singlet dynamics, which plays a major role in the physics of the spin-1/2 quantum Heisenberg antiferromagnet (QHAF) on the kagome lattice, can be approximately described by projecting onto the nearest-neighbor valence bond (NNVB) singlet subspace. We revisit here the effective quantum dimer model, which originates from the latter NNVB-projected Heisenberg model via a nonperturbative Rokhsar-Kivelson-like scheme. By using Lanczos exact diagonalization on a 108-site cluster supplemented by a careful symmetry analysis, it is shown that a previously found 36-site valence bond crystal (VBC) in fact competes with a new type of 12-site "resonating-columnar" VBC. Interestingly, these two VBCs "emerge" in different topological sectors. The exceptionally large degeneracy of the ground-state multiplets (144 on our 108-site cluster) and the proximity of a Z 2 dimer liquid have implications for the interpretation of numerical results on the QHAF, which are outlined. The possibility of a chiral VBC (i.e., spontaneously breaking time-reversal symmetry) is also discussed. © 2011 American Physical Society. Source

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