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Ellis, J., Hodgkinson, R. N., Lee, J. S., & Pilaftsis, A. (2010). Flavour geometry and effective Yukawa couplings in the MSSM. J. High Energy Phys., 02(2), 016–35pp.
Abstract: We present a new geometric approach to the flavour decomposition of an arbitrary soft supersymmetry-breaking sector in the MSSM. Our approach is based on the geometry that results from the quark and lepton Yukawa couplings, and enables us to derive the necessary and sufficient conditions for a linearly-independent basis of matrices related to the completeness of the internal [SU(3) circle times U(1)](5) flavour space. In a second step, we calculate the effective Yukawa couplings that are enhanced at large values of tan beta for general soft supersymmetry-breaking mass parameters. We highlight the contributions due to non-universal terms in the flavour decompositions of the sfermion mass matrices. We present numerical examples illustrating how such terms are induced by renormalization-group evolution starting from universal input boundary conditions, and demonstrate their importance for the flavour-violating effective Yukawa couplings of quarks.
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Ferrario, P., & Rodrigo, G. (2010). Heavy colored resonances in t(t)over-bar + jet at the LHC. J. High Energy Phys., 02(2), 051–13pp.
Abstract: The LHC is the perfect environment for the study of new physics in the top quark sector. We study the possibility of detecting signals of heavy color-octet vector resonances, through the charge asymmetry, in t (t) over bar + jet events. Besides contributions with the t (t) over bar pair in a color-singlet state, the asymmetry gets also contributions which are proportional to the color factor f(abc)(2). This process is particularly interesting for extra-dimensional models, where the inclusive charge asymmetry generated by Kaluza-Klein excitations of the gluon vanishes at the tree level. We find that the statistical significance for the measurement of such an asymmetry is sizable for different values of the coupling constants and already at low energies.
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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.
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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).
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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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Baron, R., Boucaud, P., Carbonell, J., Deuzeman, A., Drach, V., Farchioni, F., et al. (2010). Light hadrons from lattice QCD with light (u, d), strange and charm dynamical quarks. J. High Energy Phys., 06(6), 111–31pp.
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Aguilar, A. C., Binosi, D., & Papavassiliou, J. (2010). QCD effective charges from lattice data. J. High Energy Phys., 07(7), 002–24pp.
Abstract: We use recent lattice data on the gluon and ghost propagators, as well as the Kugo-Ojima function, in order to extract the non-perturbative behavior of two particular definitions of the QCD effective charge, one based on the pinch technique construction, and one obtained from the standard ghost-gluon vertex. The construction relies crucially on the definition of two dimensionful quantities, which are invariant under the renormalization group, and are built out of very particular combinations of the aforementioned Green's functions. The main non-perturbative feature of both effective charges, encoded in the infrared finiteness of the gluon propagator and ghost dressing function used in their definition, is the freezing at a common finite (non-vanishing) value, in agreement with a plethora of theoretical and phenomenological expectations. We discuss the sizable discrepancy between the freezing values obtained from the present lattice analysis and the corresponding estimates derived from several phenomenological studies, and attribute its origin to the difference in the gauges employed. A particular toy calculation suggests that the modifications induced to the non-perturbative gluon propagator by the gauge choice may indeed account for the observed deviation of the freezing values.
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Baron, R., Boucaud, P., Dimopoulos, P., Frezzotti, R., Palao, D., Rossi, G., et al. (2010). Light meson physics from maximally twisted mass lattice QCD. J. High Energy Phys., 08(8), 097–41pp.
Abstract: We present a comprehensive investigation of light meson physics using maximally twisted mass fermions for N-f = 2 mass-degenerate quark flavours. By employing four values of the lattice spacing, spatial lattice extents ranging from 2.0 fm to 2.5 fm and pseudo scalar masses in the range 280 less than or similar to m(PS) less than or similar to 650MeV we control the major systematic effects of our calculation. This enables us to confront our N-f = 2 data with SU(2) chiral perturbation theory and extract low energy constants of the effective chiral Lagrangian and derived quantities, such as the light quark mass.
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Edelhauser, L., Porod, W., & Singh, R. K. (2010). Spin discrimination in three-body decays. J. High Energy Phys., 08(8), 053–31pp.
Abstract: The identification of the correct model for physics beyond the Standard Model requires the determination of the spin of new particles. We investigate to which extent the spin of a new particle X can be identified in scenarios where it decays dominantly in three-body decays X -> f (f) over barY. Here we assume that Y is a candidate for dark matter and escapes direct detection at a high energy collider such as the LHC. We show that in the case that all intermediate particles are heavy, one can get information on the spins of X and Y at the LHC by exploiting the invariant mass distribution of the two standard model fermions. We develop a model-independent strategy to determine the spins without prior knowledge of the unknown couplings and test it in a series of Monte Carlo studies.
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