1,721,143 research outputs found
Noncommutative spectral geometry, Bogoliubov transformations and neutrino oscillations
Full text linkIn this report we show that neutrino mixing is intrinsically contained in Connes' noncommutatives pectral geometry construction, thanks to the introduction of the doubling of algebra, which is connected to the Bogoliubov transformation. It is known indeed that these transformations are responsible for the mixing, turning the mass vacuum state into the flavor vacuum state, in such a way that mass and flavor vacuum states are not unitary equivalent. There is thus a red thread that binds the doubling of algebra of Connes' model to the neutrino mixing.</p
Spectral regularisation: Induced gravity and the onset of inflation
Full text linkUsing spectral regularisation, we compute the Weyl anomaly and express the anomaly generating functional of the quantum effective action through a collective scalar degree of freedom of all quantum vacuum fluctuations. Such a formulation allows us to describe induced gravity on an equal footing with the anomaly-induced effective action, in a self-consistent way. We then show that requiring stability of the cosmological constant under loop quantum corrections, Sakharov's induced gravity and Starobinsky's anomaly-induced inflation are either both present or both absent, depending on the particle content of the theory.</p
Noncommutative spectral geometry and the deformed Hopf algebra structure of quantum field theory
Full text linkWe report the results obtained in the study of Alain Connes noncommutative spectral geometry construction focusing on its essential ingredient of the algebra doubling. We show that such a two-sheeted structure is related with the gauge structure of the theory, its dissipative character and carries in itself the seeds of quantization. From the algebraic point of view, the algebra doubling process has the same structure of the deformed Hops algebra structure which characterizes quantum field theory. © Published under licence by IOP Publishing Ltd
Constraints on extended gravity models through gravitational wave emission
No full textUsing recent experimental results of detection of gravitational waves from the binary black hole signals by Advanced LIGO and Advanced Virgo, we investigate the propagation of gravitational waves in the context of fourth order gravity nonminimally coupled to a massive scalar field. Gravitational radiation admits extra massive modes of oscillation and we assume that the amplitude of these modes is comparable to that of the massless mode. We derive the propagation equation and effective mass for each degree of freedom and we infer, from the current observational data, constraints on the free parameters of the gravity models we considered. In particular, for f(R)=R-R2/R0, the constraint obtained from the speed of gravitational waves is not compatible with the one set by Solar System tests, which implies that amplitude of the massive modes could not be detectable with current experiments on Earth.Using recent experimental results of detection of gravitational waves from the binary black hole signals by Advanced LIGO and Advanced Virgo, we investigate the propagation of gravitational waves in the context of fourth order gravity nonminimally coupled to a massive scalar field. Gravitational radiation admits extra massive modes of oscillation and we assume that the amplitude of these modes is comparable to that of the massless mode. We derive the propagation equation and effective mass for each degree of freedom and we infer, from the current observational data, constraints on the free parameters of the gravity models we considered. In particular, for , the constraint obtained from the speed of gravitational waves is not compatible with the one set by Solar System tests, which implies that amplitude of the massive modes could not be detectable with current experiments on Eart
Effective cosmological constant induced by stochastic fluctuations of Newton's constant
Full text linkWe consider implications of the microscopic dynamics of spacetime for the
evolution of cosmological models. We argue that quantum geometry effects may
lead to stochastic fluctuations of the gravitational constant, which is thus
considered as a macroscopic effective dynamical quantity. Consistency with
Riemannian geometry entails the presence of a time-dependent dark energy term
in the modified field equations, which can be expressed in terms of the
dynamical gravitational constant. We suggest that the late-time accelerated
expansion of the Universe may be ascribed to quantum fluctuations in the
geometry of spacetime rather than the vacuum energy from the matter sector.Comment: 10 pages, 1 figure, v2: added legend in Fig.1 and a referenc
Single Field Inflation and non-Gaussianity
Full text linkWe study non-Gaussian signatures on the cosmic microwave background (CMB) radiation predicted within inflationary models with non-vacuum initial states for cosmological perturbations. The model incorporates a privileged scale, which implies the existence of a feature in the primordial power spectrum. This broken-scale-invariant model predicts a vanishing three-point correlation function for the CMB temperature anisotropies (or any other odd-numbered-point correlation function) whilst an intrinsic non-Gaussian signature arises for any even-numbered-point correlation function. We thus focus on the first non-vanishing moment, the CMB four-point function at zero lag, namely the kurtosis, and compute its expected value for different locations of the primordial feature in the spectrum, as suggested in the literature to conform with observations of large scale structure. The excess kurtosis is found to be negative and the signal to noise ratio for the dimensionless excess kurtosis parameter is equal to |S/N≃4×10−4, almost independently of the free parameters of the model. This signature turns out to be undetectable. We conclude that, subject to current tests, Gaussianity is a generic property of single field inflationary models. The only uncertainty concerning this prediction is that the effect of back reaction has not yet been properly incorporated. The implications for the trans-Planckian problem of inflation are also briefly discussed.Fil: Gangui, Alejandro. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Martin, Jerome. Institut d’Astrophysique de Paris; FranciaFil: Sakellariadou, Mairi. University of Athens; Greci
Does gravity’s rainbow induce inflation without an inflaton?
No full textWe study aspects of quantum cosmology in the presence of modified space-time geometry. In particular, within the context of gravity's rainbow modified geometry, motivated from quantum gravity corrections at the Planck energy scale, we show that the distortion of the metric leads to a Wheeler-DeWitt equation whose solution admits outgoing plane waves. Hence, a period of cosmological inflation may arise without the need of introducing an inflaton field
Space–time dimensionality from brane collisions
No full textAbstractCollisions and subsequent decays of higher dimensional branes leave behind three-dimensional branes and anti-branes, one of which could play the rôle of our universe. This process also leads to the production of one-dimensional branes and anti-branes, however their number is expected to be suppressed. Brane collisions may also lead to the formation of bound states of branes. Their existence does not alter this result, it just allows for the existence of one-dimensional branes captured within the three-dimensional ones
Fermionic spectral action and the origin of nonzero neutrino masses
Full text linkWe propose that the fermionic part of the action in the framework of the noncommutative description of the Standard Model is spectral, in an analogous way to the bosonic part of the action that is customary considered as being spectral. We then discuss the terms that appear in the asymptotic expansion of the fermionic spectral action
Inflation mechanism in asymptotic noncommutative geometry
No full textAbstractThe possibility of having an inflationary epoch within a noncommutative geometry approach to unifying gravity and the Standard Model is demonstrated. This inflationary phase occurs without the need to introduce ad hoc additional fields or potentials, rather it is a consequence of a nonminimal coupling between the geometry and the Higgs field
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