22 research outputs found
On predictions from spontaneously broken flavor symmetries
We discuss the predictive power of supersymmetric models with flavor
symmetries, focusing on the lepton sector of the standard model. In particular,
we comment on schemes in which, after certain `flavons' acquire their vacuum
expectation values (VEVs), the charged lepton Yukawa couplings and the neutrino
mass matrix appear to have certain residual symmetries. In most analyses, only
corrections to the holomorphic superpotential from higher-dimensional operators
are considered (for instance, in order to generate a realistic
mixing angle). In general, however, the flavon VEVs also modify the K\"ahler
potential and, therefore, the model predictions. We show that these corrections
to the naive results can be sizable. Furthermore, we present simple analytic
formulae that allow us to understand the impact of these corrections on the
predictions for the masses and mixing parameters.Comment: 12 pages, 4 figures; improved version matching PLB articl
Predictivity of models with spontaneously broken non-Abelian discrete flavor symmetries
In a class of supersymmetric flavor models predictions are based on residual
symmetries of some subsectors of the theory such as those of the charged
leptons and neutrinos. However, the vacuum expectation values of the so-called
flavon fields generally modify the K\"ahler potential of the setting, thus
changing the predictions. We derive simple analytic formulae that allow us to
understand the impact of these corrections on the predictions for the masses
and mixing parameters. Furthermore, we discuss the effects on the vacuum
alignment and on flavor changing neutral currents. Our results can also be
applied to non--supersymmetric flavor models.Comment: 34 pages, 4 figures, related Mathematica package can be found at
http://einrichtungen.ph.tum.de/T30e/codes/KaehlerCorrections/, updated
version with added reference, matching NPB articl
A solid state light-matter interface at the single photon level
Coherent and reversible mapping of quantum information between light and
matter is an important experimental challenge in quantum information science.
In particular, it is a decisive milestone for the implementation of quantum
networks and quantum repeaters. So far, quantum interfaces between light and
atoms have been demonstrated with atomic gases, and with single trapped atoms
in cavities. Here we demonstrate the coherent and reversible mapping of a light
field with less than one photon per pulse onto an ensemble of 10 millions atoms
naturally trapped in a solid. This is achieved by coherently absorbing the
light field in a suitably prepared solid state atomic medium. The state of the
light is mapped onto collective atomic excitations on an optical transition and
stored for a pre-programmed time up of to 1 mu s before being released in a
well defined spatio-temporal mode as a result of a collective interference. The
coherence of the process is verified by performing an interference experiment
with two stored weak pulses with a variable phase relation. Visibilities of
more than 95% are obtained, which demonstrates the high coherence of the
mapping process at the single photon level. In addition, we show experimentally
that our interface allows one to store and retrieve light fields in multiple
temporal modes. Our results represent the first observation of collective
enhancement at the single photon level in a solid and open the way to multimode
solid state quantum memories as a promising alternative to atomic gases.Comment: 5 pages, 5 figures, version submitted on June 27 200
Towards high-speed optical quantum memories
Quantum memories, capable of controllably storing and releasing a photon, are
a crucial component for quantum computers and quantum communications. So far,
quantum memories have operated with bandwidths that limit data rates to MHz.
Here we report the coherent storage and retrieval of sub-nanosecond low
intensity light pulses with spectral bandwidths exceeding 1 GHz in cesium
vapor. The novel memory interaction takes place via a far off-resonant
two-photon transition in which the memory bandwidth is dynamically generated by
a strong control field. This allows for an increase in data rates by a factor
of almost 1000 compared to existing quantum memories. The memory works with a
total efficiency of 15% and its coherence is demonstrated by directly
interfering the stored and retrieved pulses. Coherence times in hot atomic
vapors are on the order of microsecond - the expected storage time limit for
this memory.Comment: 13 pages, 5 figure
The mu term and neutrino masses
The well-known Giudice-Masiero mechanism explains the presence of a mu term
of the order of the gravitino mass, but does not explain why the holomorphic
mass term is absent in the superpotential. We discuss anomaly-free discrete
symmetries which are both compatible with SU(5) unification of matter and the
Giudice-Masiero mechanism, i.e. forbid the mu term in the superpotential while
allowing the necessary Kaehler potential term. We find that these are Z_M^R
symmetries with the following properties: (i) M is a multiple of four; (ii) the
Higgs bilinear H_u H_d transforms trivially; (iii) the superspace coordinate
theta has charge M/4 and, accordingly, the superpotential has charge M/2; (iv)
dimension five proton decay operators are automatically absent. All Z_M^R
symmetries are anomaly-free due to a non-trivial transformation of a
Green-Schwarz axion, and, as a consequence, a holomorphic mu term appears at
the non-perturbative level. There is a unique symmetry that is consistent with
the Weinberg operator while there is a class of Z_M^R symmetries which explain
suppressed Dirac neutrino masses.Comment: 24 page