55 research outputs found
Holographic evolution of gauge couplings
No full textWe study the gauge coupling evolution of a unified theory in the compact Randall-Sundrum model with gauge bosons propagating in the bulk. One-loop corrections in AdS are interpreted in the 4d dual theory as the sum of two contributions: CFT insertions subleading in a 1/N expansion and loops of the additional particles coupled to the CFT. We have calculated the scalar loop correction to the low energy gauge couplings both in scenarios where the GUT symmetry is broken by boundary conditions and with the Higgs mechanism. In each case our results are what expected from the holographic dual theory
Collider signals of brane fluctuations
No full textAssuming that we live on a non rigid brane with TeV-scale tension, the scalar fields that control the coordinates of our brane in the extra dimensions give rise to missing energy signals at high-energy colliders with a characteristic angular and energy spectrum, identical to the one due to graviton emission in 6 extra dimensions. LEP bounds and LHC capabilities are analyzed. (C) 2001 Elsevier Science B.V. All rights reserved
Frequentist analyses of solar neutrino data
No full textThe solar neutrino data are analyzed in a frequentist framework, using the Crow-Gardner and Feldman-Cousins prescriptions for the construction of confidence regions. Including in the fit only the total rates measured by the various experiments, both methods give results similar to the commonly used Delta chi^2-cut approximation. When fitting the full data set, the Delta chi^2-cut still gives a good approximation of the Feldman-Cousins regions. However, a careful statistical analysis significantly reduces the goodness-of-fit of the SMA and LOW solutions.The solar neutrino data are analyzed in a frequentist framework, using the Crow-Gardner and Feldman-Cousins prescriptions for the construction of confidence regions. Including in the fit only the total rates measured by the various experiments, both methods give results similar to the commonly used Delta chi^2-cut approximation. When fitting the full data set, the Delta chi^2-cut still gives a good approximation of the Feldman-Cousins regions. However, a careful statistical analysis significantly reduces the goodness-of-fit of the SMA and LOW solutions. In the addenda we discuss the implications of the latest KamLAND, SNO and SK data
Non-linear Representations of the Conformal Group and Mapping of Galileons
No full textThere are two common non-linear realizations of the 4D conformal group: in the first, the dilaton is the conformal factor of the effective metric \eta_{\mu\nu} e^{-2 \pi}; in the second it describes the fluctuations of a brane in AdS_5. The two are related by a complicated field redefinition, found by Bellucci, Ivanov and Krivonos (2002) to all orders in derivatives. We show that this field redefinition can be understood geometrically as a change of coordinates in AdS_5. In one gauge the brane is rigid at a fixed radial coordinate with a conformal factor on the AdS_5 boundary, while in the other one the brane bends in an unperturbed AdS_5. This geometrical picture illuminates some aspects of the mapping between the two representations. We show that the conformal Galileons in the two representations are mapped into each other in a quite non-trivial way: the DBI action, for example, is mapped into a complete linear combination of all the five Galileons in the other representation. We also verify the equivalence of the dilaton S-matrix in the two representations and point out that the aperture of the dilaton light-cone around non-trivial backgrounds is not the same in the two representations
Neutrino oscillations and large extra dimensions
No full textAssuming that right-handed neutrinos exist and propagate in some large extra dimensions, we attempt to give a comprehensive description of the phenomenology of neutrino oscillations. A few alternative explanations of the atmospheric neutrino anomaly emerge, different from the standard nu(mu) --> nu(tau) or nu(mu) --> nu(sterile) interpretations. Constraints from nucleosynthesis and supernova 1987a are discussed. The constraints from SN1987a indicates a maximum radius of any extra dimension of about 1 Angstrom. (C) 2000 Elsevier Science B.V. All rights reserved
Neutrino mixings from a U(2) flavour symmetry
No full textWe extend a previously developed description of the flavour parameters in the charged fermion sector, based on a U(2) flavour symmetry, to include two main features of the neutrino sector seemingly implied by recent data: a large mixing angle theta(mu tau) and a large hierarchy in the neutrino squared mass differences. A unified description of quark and lepton masses and mixings emerges, The neatest quantitative predictions are for elements of the unitary mixing matrix in the lepton sector [GRAPHICS] which go together with the analogous relations in the quark sector [GRAPHICS] (C) 1999 Elsevier Science B.V. All rights reserved
Baryogenesis through leptogenesis
No full textBaryogenesis by heavy-neutrino decay and sphaleron reprocessing of both baryon and lepton number is reconsidered, paying special attention to the flavour structure of the general evolution equations and developing an approximate but sufficiently accurate analytic solution to the prototype evolution equation. Two different models of neutrino masses are examined, based on an Abelian U(1) or a non-Abelian U(2) family symmetry. We show that a consistent picture of baryogenesis can emerge in both cases, although with significant differences. (C) 2000 Elsevier Science B.V. All rights reserved
Ghosts in massive gravity
No full textIn the context of Lorentz-invariant massive gravity we show that classical solutions around heavy sources are plagued by ghost instabilities. The ghost shows up in the effective field theory at huge distances from the source, much bigger than the Vainshtein radius. Its presence is independent of the choice of the non-linear terms added to the Fierz-Pauli lagrangian. At the Vainshtein radius the mass of the ghost is of order of the inverse radius, so that the theory cannot be trusted inside this region, not even at the classical level
Sachs-Wolfe at second order: the CMB bispectrum on large angular scales
No full textWe calculate the Cosmic Microwave Background anisotropy bispectrum on large angular scales in the absence of primordial non-Gaussianities, assuming exact matter dominance and extending at second order the classic Sachs-Wolfe result delta T/T = Phi/3. The calculation is done in Poisson gauge. Besides intrinsic contributions calculated at last scattering, one must consider integrated effects. These are associated to lensing, and to the time dependence of the potentials (Rees-Sciama) and of the vector and tensor components of the metric generated at second order. The bispectrum is explicitly computed in the flat-sky approximation. It scales as l(-4) in the scale invariant limit and the shape dependence of its various contributions is represented in 3d plots. Although all the contributions to the bispectrum are parametrically of the same order, the full bispectrum is dominated by lensing. In the squeezed limit it corresponds to f(NL)(local) = -1/6 - cos(2 theta), where theta is the angle between the short and the long modes; the angle dependent contribution comes from lensing. In the equilateral limit it corresponds to f(NL)(equil) similar or equal to 3.13.It is a pleasure to thank Nicola Bartolo, Francis Bernardeau, Eiichiro Komatsu, Roy Maartens,Sabino Matarrese, Toni Riotto, Misao Sasaki, Uros Seljak, Leonardo Senatore and Matias Zaldarriaga for useful discussions. G.D’A. and P.C. thank the Institut de Physique Th´eorique at Saclay and
F.V. thanks the ICTP for hospitality while working on this project. G.D’A., P.C., and F.V. thank the Galileo Galilei Institute, where part of this work was carried out during the workshop “New Horizons for Modern Cosmology”. Furthermore, F.V. thanks the Yukawa Institute for Theoretical Physics at Kyoto University, where part of this work was carried out during the GCOE/YITP workshop
YITP-W-09-01 on “Non-linear cosmological perturbations” and the EU Marie Curie Research and Training network ”UniverseNet” (MRTN-CT-2006-035863) for support..Peer reviewe
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