5,619 research outputs found
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
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