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Bordes, J., Dominguez, C. A., Moodley, P., Peñarrocha, J., & Schilcher, K. (2010). Chiral corrections to the SU(2) x SU(2) Gell-Mann-Oakes-Renner relation. J. High Energy Phys., 05(5), 064–16pp.
Abstract: The next to leading order chiral corrections to the SU(2) x SU(2) Gell-Mann-Oakes- Renner (GMOR) relation are obtained using the pseudoscalar correlator to five-loop order in perturbative QCD, together with new finite energy sum rules (FESR) incorporating polynomial, Legendre type, integration kernels. The purpose of these kernels is to suppress hadronic contributions in the region where they are least known. This reduces considerably the systematic uncertainties arising from the lack of direct experimental information on the hadronic resonance spectral function. Three different methods are used to compute the FESR contour integral in the complex energy (squared) s-plane, i.e. Fixed Order Perturbation Theory, Contour Improved Perturbation Theory, and a fixed renormalization scale scheme. We obtain for the corrections to the GMOR relation, delta(pi), the value delta(pi) = (6.2 +/- 1.6)%. This result is substantially more accurate than previous determinations based on QCD sum rules; it is also more reliable as it is basically free of systematic uncertainties. It implies a light quark condensate < 0 vertical bar(u) over baru vertical bar 0 > similar or equal to < 0 vertical bar(d) over bard vertical bar 0 > < 0 vertical bar(q) over barq vertical bar 0 >vertical bar(2GeV) = (-267 +/- 5MeV)(3). As a byproduct, the chiral perturbation theory (unphysical) low energy constant H-2(r) is predicted to be H-2(r)(nu(X) = M-p) = -(5.1 +/- 1.8) x10(-3), or H-2(r) (nu(X) = M-eta) = -(5.7 +/- 2.0) x10(-3).
Keywords: QCD Phenomenology
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Cabrera, M. E., Casas, J. A., & Ruiz de Austri, R. (2010). MSSM forecast for the LHC. J. High Energy Phys., 05(5), 043–48pp.
Abstract: We perform a forecast of the MSSM with universal soft terms (CMSSM) for the LHC, based on an improved Bayesian analysis. We do not incorporate ad hoc measures of the fine-tuning to penalize unnatural possibilities: such penalization arises from the Bayesian analysis itself when the experimental value of M-Z is considered. This allows to scan the whole parameter space, allowing arbitrarily large soft terms. Still the low-energy region is statistically favoured (even before including dark matter or g-2 constraints). Contrary to other studies, the results are almost unaffected by changing the upper limits taken for the soft terms. The results are also remarkable stable when using flat or logarithmic priors, a fact that arises from the larger statistical weight of the low-energy region in both cases. Then we incorporate all the important experimental constrains to the analysis, obtaining a map of the probability density of the MSSM parameter space, i.e. the forecast of the MSSM. Since not all the experimental information is equally robust, we perform separate analyses depending on the group of observables used. When only the most robust ones are used, the favoured region of the parameter space contains a significant portion outside the LHC reach. This effect gets reinforced if the Higgs mass is not close to its present experimental limit and persits when dark matter constraints are included. Only when the g-2 constraint (based on e(+)e(-) data) is considered, the preferred region (for μ> 0) is well inside the LHC scope. We also perform a Bayesian comparison of the positive- and negative-mu possibilities.
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Boubekeur, L., Choi, K. Y., Ruiz de Austri, R., & Vives, O. (2010). The degenerate gravitino scenario. J. Cosmol. Astropart. Phys., 04(4), 005–26pp.
Abstract: In this work, we explore the “degenerate gravitino” scenario where the mass difference between the gravitino and the lightest MSSM particle is much smaller than the gravitino mass itself. In this case, the energy released in the decay of the next to lightest sypersymmetric particle (NLSP) is reduced. Consequently the cosmological and astrophysical constraints on the gravitino abundance, and hence on the reheating temperature, become softer than in the usual case. On the other hand, such small mass splittings generically imply a much longer lifetime for the NLSP. We find that, in the constrained MSSM (CMSSM), for neutralino LSP or NLSP, reheating temperatures compatible with thermal leptogenesis are reached for small splittings of order 10(-2) GeV. While for stau NLSP, temperatures of T-RH similar or equal to 4 x 10(9) GeV can be obtained even for splittings of order of tens of GeVs. This “degenerate gravitino” scenario offers a possible way out to the gravitino problem for thermal leptogenesis in supersymmetric theories.
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Jackson, C. B., Servant, G., Shaughnessy, G., Tait, T. M. P., & Taoso, M. (2010). Higgs in space! J. Cosmol. Astropart. Phys., 04(4), 004–29pp.
Abstract: We consider the possibility that the Higgs can be produced in dark matter annihilations, appearing as a line in the spectrum of gamma rays at an energy determined by the masses of the WIMP and the Higgs itself. We argue that this phenomenon occurs generally in models in which the the dark sector has large couplings to the most massive states of the SM and provide a simple example inspired by the Randall-Sundrum vision of dark matter, whose 4d dual corresponds to electroweak symmetry-breaking by strong dynamics which respect global symmetries that guarantee a stable WIMP. The dark matter is a Dirac fermion that couples to a Z' acting as a portal to the Standard Model through its strong coupling to top quarks. Annihilation into light standard model degrees of freedom is suppressed and generates a feeble continuum spectrum of gamma rays. Loops of top quarks mediate annihilation into gamma Z, gamma h, and gamma Z', providing a forest of lines in the spectrum. Such models can be probed by the Fermi/GLAST satellite and ground-based Air Cherenkov telescopes.
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Bustamante, M., Gago, A. M., & Pena-Garay, C. (2010). Energy-independent new physics in the flavour ratios of high-energy astrophysical neutrinos. J. High Energy Phys., 04(4), 066–28pp.
Abstract: We have studied the consequences of breaking the CPT symmetry in the neutrino sector, using the expected high-energy neutrino flux from distant cosmological sources such as active galaxies. For this purpose we have assumed three different hypotheses for the neutrino production model, characterised by the flavour fluxes at production phi(0)(e) : phi(0)(mu) : phi(0)(tau) = 1 : 2 : 0, 0 : 1 : 0, and 1 : 0 : 0, and studied the theoretical and experimental expectations for the muon-neutrino flux at Earth, phi(mu), and for the flavour ratios at Earth, R = phi(mu)/phi(e) and S = phi(tau)/phi(mu). CPT violation (CPTV) has been implemented by adding an energy-independent term to the standard neutrino oscillation Hamiltonian. This introduces three new mixing angles, two new eigenvalues and three new phases, all of which have currently unknown values. We have varied the new mixing angles and eigenvalues within certain bounds, together with the parameters associated to pure standard oscillations. Our results indicate that, for the models 1 : 2 : 0 and 0 : 1 : 0, it might be possible to find large deviations of phi(mu), R, and S between the cases without and with CPTV, provided the CPTV eigenvalues lie within 10(-29) – 10(-27) GeV, or above. Moreover, if CPTV exists, there are certain values of R and S that can be accounted for by up to three production models. If no CPTV were observed, we could set limits on the CPTV eigenvalues of the same order. Detection prospects calculated using IceCube suggest that for the models 1 : 2 : 0 and 0 : 1 : 0, the modifications due to CPTV are larger and more clearly separable from the standard-oscillations predictions. We conclude that IceCube is potentially able to detect CPTV but that, depending on the values of the CPTV parameters, there could be a mis-determination of the neutrino production model.
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Bernard, V., & Passemar, E. (2010). Chiral extrapolation of the strangeness changing scalar K pi form factor. J. High Energy Phys., 04(4), 001–18pp.
Abstract: We perform a chiral extrapolation of lattice data on the scalar K pi form factor and the ratio of the kaon and pion decay constants within Chiral Perturbation Theory to two loops. We determine the value of the scalar form factor at zero momentum transfer, at the Callan-Treiman point and at its soft kaon analog as well as its slope. Results are in good agreement with their determination from experiment using the standard couplings of quarks to the W boson. The slope is however rather large. A study of the convergence of the chiral expansion is also performed.
Keywords: Lattice QCD; Chiral Lagrangians
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Botella, F. J., Branco, G. C., & Rebelo, M. N. (2010). Minimal flavour violation and multi-Higgs models. Phys. Lett. B, 687(2-3), 194–200.
Abstract: We propose an extension of the hypothesis of Minimal Flavour Violation (MFV) to general multi-Higgs models without the assumption of Natural Flavour Conservation (NFC) in the Higgs sector. We study in detail under what conditions the neutral Higgs couplings are only functions of V-CKM and propose a MFV expansion for the neutral Higgs couplings to fermions.
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Choi, K. Y., Lopez-Fogliani, D. E., Muñoz, C., & Ruiz de Austri, R. (2010). Gamma-ray detection from gravitino dark matter decay in the μnu SSM. J. Cosmol. Astropart. Phys., 03(3), 028–14pp.
Abstract: The μnu SSM provides a solution to the mu-problem of the MSSM and explains the origin of neutrino masses by simply using right-handed neutrino superfields. Given that R-parity is broken in this model, the gravitino is a natural candidate for dark matter since its lifetime becomes much longer than the age of the Universe. We consider the implications of gravitino dark matter in the μnu SSM, analyzing in particular the prospects for detecting gamma rays from decaying gravitinos. If the gravitino explains the whole dark matter component, a gravitino mass larger than 20 GeV is disfavored by the isotropic diffuse photon background measurements. On the other hand, a gravitino with a mass range between 0.1 – 20 GeV gives rise to a signal that might be observed by the FERMI satellite. In this way important regions of the parameter space of the μnu SSM can be checked.
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Barenboim, G., Fernandez-Martinez, E., Mena, O., & Verde, L. (2010). The dark side of curvature. J. Cosmol. Astropart. Phys., 03(3), 008–17pp.
Abstract: Geometrical tests such as the combination of the Hubble parameter H(z) and the angular diameter distance d(A)(z) can, in principle, break the degeneracy between the dark energy equation of state parameter w(z), and the spatial curvature Omega(k) in a direct, model-independent way. In practice, constraints on these quantities achievable from realistic experiments, such as those to be provided by Baryon Acoustic Oscillation (BAO) galaxy surveys in combination with CMB data, can resolve the cosmic confusion between the dark energy equation of state parameter and curvature only statistically and within a parameterized model for w(z). Combining measurements of both H(z) and d(A)(z) up to sufficiently high redshifts z similar to 2 and employing a parameterization of the redshift evolution of the dark energy equation of state are the keys to resolve the w(z) – Omega(k) degeneracy.
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Labiche, M. et al, Caballero, L., & Rubio, B. (2010). TIARA: A large solid angle silicon array for direct reaction studies with radioactive beams. Nucl. Instrum. Methods Phys. Res. A, 614(3), 439–448.
Abstract: A compact, quasi-4 pi position sensitive silicon array. TIARA, designed to study direct reactions induced by radioactive beams in inverse kinematics is described here. The Transfer and Inelastic All-angle Reaction Array (TIARA) consists of 8 resistive charge division detectors forming an octagonal barrel around the target and a set of double-sided silicon-strip annular detectors positioned at each end of the barrel. The detector was coupled to the gamma-ray array EXOGAM and the spectrometer VAMOS at the GANIL Laboratory to demonstrate the potential of such an apparatus with radioactive beams. The N-14(d,p)N-15 reaction, well known in direct kinematics, has been carried out in inverse kinematics for that purpose. The observation of the N-15 ground state and excited states at 7.16 and 7.86 MeV is presented here as well as the comparison of the measured proton angular distributions with DWBA calculations. Transferred l-values are in very good agreement with both theoretical calculations and previous experimental results obtained in direct kinematics.
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