6,007 research outputs found
Maximally correlated multipartite quantum states
We investigate quantum states that posses both maximum entanglement and
maximum discord between the pertinent parties. Since entanglement (discord) is
defined only for bipartite (two qubit) systems, we shall introduce an
appropriate sum over of all bi-partitions as the associated measure. The
ensuing definition --not new for entanglement-- is thus extended here to
quantum discord. Also, additional dimensions within the parties are considered
({\it qudits}). We also discuss nonlocality (in the form of maximum violation
of a Bell inequality) for all multiqubit systems. The emergence of more
nonlocal states than local ones, all of them possessing maximum entanglement,
will be linked, surprisingly enough, to whether quantum mechanics is defined
over the fields of real or complex numbers.Comment: 13 pages, 5 figures, 2 table
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
The 750 GeV Diphoton Excess as a First Light on Supersymmetry Breaking
One of the most exciting explanations advanced for the recent diphoton excess
found by ATLAS and CMS is in terms of sgoldstino decays: a signal of low-energy
supersymmetry-breaking scenarios. The sgoldstino, a scalar, couples directly to
gluons and photons, with strength related to gaugino masses, that can be of the
right magnitude to explain the excess. However, fitting the suggested resonance
width, Gamma ~ 45 GeV, is not so easy. In this paper we explore efficient
possibilities to enhance the sgoldstino width, via the decay into two Higgses,
two Higgsinos and through mixing between the sgoldstino and the Higgs boson. In
addition, we present an alternative and more efficient mechanism to generate a
mass splitting between the scalar and pseudoscalar components of the
sgoldstino, which has been suggested as an interesting alternative explanation
to the apparent width of the resonance.Comment: 14 pages, 3 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
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
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