3,881 research outputs found
Absorption-free optical control of spin systems:the quantum Zeno effect in optical pumping
We show that atomic spin motion can be controlled by circularly polarized
light without light absorption in the strong pumping limit. In this limit, the
pumping light, which drives the empty spin state, destroys the Zeeman coherence
effectively and freezes the coherent transition via the quantum Zeno effect. It
is verified experimentally that the amount of light absorption decreases
asymptotically to zero as the incident light intensity is increased.Comment: 4 pages with 4 figure
Supersymmetry, Naturalness, and Signatures at the LHC
Weak scale supersymmetry is often said to be fine-tuned, especially if the
matter content is minimal. This is not true if there is a large A term for the
top squarks. We present a systematic study on fine-tuning in minimal
supersymmetric theories and identify low energy spectra that do not lead to
severe fine-tuning. Characteristic features of these spectra are: a large A
term for the top squarks, small top squark masses, moderately large tan\beta,
and a small \mu parameter. There are classes of theories leading to these
features, which are discussed. In one class, which allows a complete
elimination of fine-tuning, the Higgsinos are the lightest among all the
superpartners of the standard model particles, leading to three nearly
degenerate neutralino/chargino states. This gives interesting signals at the
LHC -- the dilepton invariant mass distribution has a very small endpoint and
shows a particular shape determined by the Higgsino nature of the two lightest
neutralinos. We demonstrate that these signals are indeed useful in realistic
analyses by performing Monte Carlo simulations, including detector simulations
and background estimations. We also present a method that allows the
determination of all the relevant superparticle masses without using input from
particular models, despite the limited kinematical information due to short
cascades. This allows us to test various possible models, which is demonstrated
in the case of a model with mixed moduli-anomaly mediation. We also give a
simple derivation of special renormalization group properties associated with
moduli mediated supersymmetry breaking, which are relevant in a model without
fine-tuning.Comment: 56 pages, 24 figure
Observation of Brewster's effect for transverse-electric electromagnetic waves in metamaterials: Experiment and theory
We have experimentally realized Brewster's effect for transverse-electric
waves with metamaterials. In dielectric media, Brewster's no-reflection effect
arises only for transverse-magnetic waves. However, it has been theoretically
predicted that Brewster's effect arises for TE waves under the condition that
the relative permeability r is not equal to unity. We have designed an array of
split-ring resonators as a metamaterial with mu_r 1 using a finite-difference
time-domain method. The reflection measurements were carried out in a 3-GHz
region and the disappearance of reflected waves at a particular incident angle
was confirmed.Comment: 4 pages, 5 figure
Making confining strings out of mesons
The light mesons such as pi, rho, omega, f0, and a0 are possible candidates
of magnetic degrees of freedom, if a magnetic dual picture of QCD exists. We
construct a linear sigma model to describe spontaneous breaking of the magnetic
gauge group, in which there is a stable vortex configuration of vector and
scalar mesons. We numerically examine whether such a string can be interpreted
as the confining string. By using meson masses and couplings as inputs, we
calculate the tension of the string as well as the strength of the Coulomb
force between static quarks. They are found to be consistent with those
inferred from the quarkonium spectrum and the Regge trajectories of hadrons. By
using the same Lagrangian, the critical temperature of the QCD phase transition
is estimated, and a non-trivial flavor dependence is predicted. We also discuss
a possible connection between the Seiberg duality and the magnetic model we
studied.Comment: 22 pages, 2 figures, 3 tables, typos corrected, references adde
Direct Mediation of Meta-Stable Supersymmetry Breaking
The supersymmetric SU(Nc) Yang-Mills theory coupled to Nf matter fields in
the fundamental representation has meta-stable vacua with broken supersymmetry
when Nc < Nf < 3/2 Nc. By gauging the flavor symmetry, this model can be
coupled directly to the standard model. We show that it is possible to make a
slight deformation to the model so that gaugino masses are generated and the
Landau pole problem can be avoided. The deformed model has simple realizations
on intersecting branes in string theory, where various features of the
meta-stable vacua are encoded geometrically as brane configurations.Comment: 22 pages, 4 figures, a reference added, version to appear in PR
Production and Polarization Effects in Some Tau-Lepton Decays
The conditions for the independence of decays of the spin-1/2 resonances on
the production mechanism of the resonances and on polarizations of the incoming
and outgoing particles are derived and applied in the case of several
tau-lepton decays. The necessity for inclusion of the influence of the
production mechanism in the evaluation of the lepton flavour violating decays
is stressed.Comment: Invited Talk at the Seventh International Workshop on Tau Lepton
Physics (TAU02), Santa Cruz, CA, USA, Sept. 2002, 6 pages LaTeX; One typo
corrected, a note added, one reference adde
Dynamical GUT breaking and mu-term driven supersymmetry breaking
Models for dynamical breaking of supersymmetric grand unified theories are
presented. The doublet-triplet splitting problem is absent since the Higgs
doublet superfields can be identified with the massless mesons of the strong
gauge group whereas there are no massless states corresponding to the colored
Higgs fields. Various strong gauge groups SU(Nc), Sp(Nc) and SO(Nc) are
examined. In a model with SO(9) strong gauge group, adding the mu-term for the
Higgs fields triggers to break supersymmetry in a meta-stable vacuum. The
pattern of the supersymmetry breaking parameters is predicted to be the
gauge-mediation type with modifications in the Higgs sector.Comment: 23 pages, 1 figure; version to appear in PR
Affleck-Dine (Pseudo)-Dirac Neutrinogenesis
We consider the Affleck-Dine mechanism for leptogenesis in the minimal MSSM
with Dirac or Pseudo-Dirac neutrinos. The rolling of scalars along D-flat
directions generates a left-right asymmetry in the sneutrino sector, only the
left part of which is transferred to a baryon asymmetry via sphaleron
transitions. In the pure Dirac case the baryon asymmetry of the Universe is
thus mirrored by an equal and opposite asymmetry in the leptons. The mechanism
is also found to work when the neutrinos are pseudo-Dirac. No additional field
needs to be added to the MSSM other than the right-handed neutrino.Comment: Latex, 3 figures, 1 bib file, 2 added reference, 1 minor correction,
1 added commen
Confronting Electroweak Fine-tuning with No-Scale Supergravity
Applying No-Scale Supergravity boundary conditions at a heavy unification
scale to the Flipped grand unified theory with extra TeV-scale
vector-like multiplets, No-Scale -, we express the
-boson mass as an explicit function of the boundary gaugino mass
, , with implicit dependence upon a
dimensionless ratio of the supersymmetric Higgs mixing parameter and
. Setting the top Yukawa coupling consistent with GeV at
GeV, the value of naturally tends toward , which
indirectly suggests underlying action of the Giudice-Masiero mechanism.
Proportional dependence of all model scales upon the unified gaugino mass
in the No-Scale - model suggests one possible
mechanism of confronting the electroweak fine tuning problem.Comment: Physics Letters B version; 8 Pages, 7 Figures, 1 Tabl
Demonstration of local expansion toward large-scale entangled webs
We demonstrate an optical gate that increases the size of polarization-based
W states by accessing only one of the qubits. Using this gate, we have
generated three-photon and four-photon W states with fidelities and , respectively. We also confirmed existence of pairwise
entanglement in every pair of the qubits including the one that was left
untouched by the gate. The gate is applicable to any size of W states and hence
is a universal tool for expanding entanglement.Comment: 5 pages, 4 figure
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