Results 1 - 10 of 3099
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[en] If the refractive index of the relic gravitons increases during a conventional stage of inflationary evolution the spectral energy density is blue at intermediate frequencies above the fHz and then flattens out after a knee that is typically smaller than the mHz. We investigate here the conditions leading to a sufficiently large spectral energy density in the nHz range where some peculiar signatures observed with the pulsar timing arrays have been recently attributed to cosmic gravitons. If these potential evidences are combined with the most recent bounds provided by wide-band interferometers in the audio range (i.e. between few Hz and the kHz) the allowed regions of the parameter space are compatible with both determinations and also with all the other constraints associated with the background of relic gravitons produced during inflation. The present analysis suggests that the pulsar timing arrays are sensitive to the evolution of the refractive index during early stages of the inflationary evolution. This physical interpretation of the preliminary empirical evidence is distinguishable from other perspectives since the high-frequency normalization, the blue spectral index and the tensor to scalar ratio cannot be independently assigned but are all related to the frequency of the knee that is ultimately determined by the competition between the rate of evolution of the refractive index and the slow-roll corrections.
[en] We consider the effect of quantum interactions on Pauli-Fierz massive gravity. With generic graviton cubic interactions, we observe that the 1-loop counterterms do not conform to the tree level structure of Pauli-Fierz action, resulting in the reappearance of the sixth mode ghost. Then to explore the quantum effects to the full extent, we calculate the resummed graviton propagator with an arbitrary interaction and analyze its complete structure, from which a minimal condition for the absence of the ghost is obtained.
[en] We study the large N anomalous dimensions of operators in a Leigh–Strassler deformation of N=4 super Yang–Mills theory. The operators that we study have a bare dimension of order N (so that the large N limit is not captured by planar diagrams) and are AdS/CFT dual to giant gravitons. The diagonalization of the dilatation operator factorizes into two problems. One of these problems is solved using a double coset ansatz. The second problem is equivalent to a set of decoupled harmonic oscillators
[en] The fermion-graviton system at linearized level in a (2+1)-dimensional space-time with the gravitational Chern-Simons term is studied. In this approximation it is shown that this system presents anomalous rotational properties and spin, in analogy with the gauge field-matter system. (A.C.A.S.)
[pt]O sistema fermion-graviton a nivel linearizado num espaco de tempo de dimensao (2+1) com termo gravitacional Chern-Simons e estudado. Nesta aproximacao mostra-se que este sistema apresenta propriedades rotacionais amomalas e spin, com amalogia ao sistema padrao campo-materia. (A.C.A.S.)
[en] Here we start from a dual version of Vasiliev’s first order action for massless spin-2 particles (linearized first order Einstein–Hilbert) and derive, via Kaluza–Klein dimensional reduction from D + 1 to D dimensions, a set of dual massive spin-2 models. This set includes the massive ‘BR’ model, a spin-2 analogue of the spin-1 Cremmer–Scherk model. In our approach the linearized Riemann curvature emerges from a solution of a functional constraint. In D = 2 + 1 the BR model can be written as a linearized version of a new bimetric model for massive gravitons. We also have a new massive spin-2 model, in arbitrary dimensions, invariant under linearized diffeomorphisms. It is given in terms of a non symmetric rank-2 tensor and a mixed symmetry tensor. (paper)
[en] We show that the LHC will be able to differentiate between a four-dimensional model with quantum gravity at ∼ 1 TeV where the (massless) graviton becomes strongly coupled to standard model particles at 1 TeV and brane world type models with a large extra-dimensional volume and massive Kaluza-Klein gravitons. We estimate that the 14 TeV LHC could put a limit of the order of ∼ 5 TeV on the four dimensional Planck mass in a model independent way.
[en] A broad range of quantum field theories of gravity predict the existence of vector and scalar components of gravity in addition to the usual tensor component. These may produce effects observable at the classical level. We refer to experimental results suggestive of the appropriate effects and show that a clear, low-energy test of these theories may be made by measuring the gravitational acceleration of antiprotons in the Earth's field