Implications for New Physics from Fine-Tuning Arguments: II. Little Higgs Models

We examine the fine-tuning associated to electroweak breaking in Little Higgs scenarios and find it to be always substantial and, generically, much higher than suggested by the rough estimates usually made. This is due to implicit tunings between parameters that can be overlooked at first glance but show up in a more systematic analysis. Focusing on four popular and representative Little Higgs scenarios, we find that the fine-tuning is essentially comparable to that of the Little Hierarchy problem of the Standard Model (which these scenarios attempt to solve) and higher than in supersymmetric models. This does not demonstrate that all Little Higgs models are fine-tuned, but stresses the need of a careful analysis of this issue in model-building before claiming that a particular model is not fine-tuned. In this respect we identify the main sources of potential fine-tuning that should be watched out for, in order to construct a successful Little Higgs model, which seems to be a non-trivial goal.Comment: 39 pages, 26 ps figures, JHEP forma

Bartering integer commodities with exogenous prices

The analysis of markets with indivisible goods and fixed exogenous prices has played an important role in economic models, especially in relation to wage rigidity and unemployment. This research report provides a mathematical and computational details associated to the mathematical programming based approaches proposed by Nasini et al. (accepted 2014) to study pure exchange economies where discrete amounts of commodities are exchanged at fixed prices. Barter processes, consisting in sequences of elementary reallocations of couple of commodities among couples of agents, are formalized as local searches converging to equilibrium allocations. A direct application of the analyzed processes in the context of computational economics is provided, along with a Java implementation of the approaches described in this research report.Comment: 30 pages, 5 sections, 10 figures, 3 table

Large mixing angles for neutrinos from infrared fixed points

Radiative amplification of neutrino mixing angles may explain the large values required by solar and atmospheric neutrino oscillations. Implementation of such mechanism in the Standard Model and many of its extensions (including the Minimal Supersymmetric Standard Model) to amplify the solar angle, the atmospheric or both requires (at least two) quasi-degenerate neutrino masses, but is not always possible. When it is, it involves a fine-tuning between initial conditions and radiative corrections. In supersymmetric models with neutrino masses generated through the Kahler potential, neutrino mixing angles can easily be driven to large values at low energy as they approach infrared pseudo-fixed points at large mixing (in stark contrast with conventional scenarios, that have infrared pseudo-fixed points at zero mixing). In addition, quasi-degeneracy of neutrino masses is not always required.Comment: 36 pages, 7 ps figure

Expectations for LHC from Naturalness: Modified vs. SM Higgs Sector

Common lore has it that naturalness of electroweak breaking in the SM requires new physics (NP) at Lambda < 2-3 TeV, hopefully within the reach of LHC. Moreover the Higgs should be light (m_h < 219 GeV) to pass electroweak precision tests (EWPT). However one should be prepared for "unexpected" (although admittedly unpleasant) results at LHC, i.e. no NP and/or a heavy Higgs. We revisit recent attempts to accommodate this by modifying the SM Higgs sector (using 2-Higgs-doublet models). We find that these models do not improve the naturalness of the SM, and so they do not change the expectations of observing NP at LHC. We also stress that a heavy SM Higgs would not be evidence in favour of a modified Higgs sector, provided certain higher order operators influence EWPT. On the other hand, we show that NP can escape LHC detection without a naturalness price, and with the pure SM as the effective theory valid at LHC energies, simply if the cut-off for top loops is slightly lower than for Higgs loops.Comment: 37 pages, LaTeX, 13 figure

Theoretical Constraints on the Vacuum Oscillation Solution to the Solar Neutrino Problem

The vacuum oscillation (VO) solution to the solar anomaly requires an extremely small neutrino mass splitting, Delta m^2_{sol}\leq 10^{-10} eV^2. We study under which circumstances this small splitting (whatever its origin) is or is not spoiled by radiative corrections. The results depend dramatically on the type of neutrino spectrum. If m_1^2 \sim m_2^2 \geq m_3^2, radiative corrections always induce too large mass splittings. Moreover, if m_1 and m_2 have equal signs, the solar mixing angle is driven by the renormalization group evolution to very small values, incompatible with the VO scenario (however, the results could be consistent with the small-angle MSW scenario). If m_1 and m_2 have opposite signs, the results are analogous, except for some small (though interesting) windows in which the VO solution may be natural with moderate fine-tuning. Finally, for a hierarchical spectrum of neutrinos, m_1^2 << m_2^2 << m_3^2, radiative corrections are not dangerous, and therefore this scenario is the only plausible one for the VO solution.Comment: 13 pages, LaTeX, 3 ps figures (psfig.sty

Estudi d' "Abutilon theophrasti medicus" com a mala herba introduïda a Lleida

L'aparició d'Abutilon theophrasti Medicus en els camps de conreu de la província de Lleida ens ha conduit a estudiar el fenomen d'introducció i la distribució actual d'aquesta nova mala herba. A. Theophrasti Med. aparegué a la zona vers l'any 1978. Començà a assolir una certa importáncia localitzada sobre el 1981 i actualment es troba en fase d'expansió. Se situa preferentment als conreus de panís de l'Urgell i la Noguera. Estimem que ja és present entre unes 1.600-2.000 ha. de terreny de regadiu, en proves de germinació en laboratori obtinguérem que un terç de les llavors d'Abutilon theophrasti Med. presenten mecanismes de dormància. Horn ofereix informació dels mètodes de control d'aquesta mala herba.The apparition of Abutilon theophrasti Medicus in the crop fields of Lleida province forced us to study the introduction fenomenon and the actual Distribution of this weed. A. Theophrasti Med. appeared in this area about 1978. It began to get local importance about 1981. Now it is spreading. It placing preferencially in irrigate maize crops of Urgell and Noguera. We consider it occuped now around 1.600-2.000 Has, of irrigation fields. A germination test we get that a 1/3 part of Abutilon theophrasti Med. seed present dormance mechanismes. This report gives information about control methods of the weed.La aparición de Abutilon theophrasti Medicos en los campos de cultivo de Lleida nos ha conducido a estudiar el fenómeno de introducción y la distribución actual de esta nueva mala hierba. A. Theophrasti Med. apareció en la zona sobre el ario 1978. Empezó a tomar cierta importancia localizada a partir de 1981 y actualment se encuentra en fase de expansión. Se sitúa preferentemente en los cultivos de maíz del Urgell y La Noguera. Estimamos que ya se encuentra presente sobre 1.600-2.000 Has. de terreno en regadío. En pruebas de germinación en laboratorio se obtuvo que un tercio de la semilla de A. Theophrasti Med. presentó mecanismos de dormancia. Se ofrece información de los métodos de control de esta mala hierba