16,307 research outputs found
Finite Higgs mass without Supersymmetry
We identify a class of chiral models where the one-loop effective potential
for Higgs scalar fields is finite without any requirement of supersymmetry. It
corresponds to the case where the Higgs fields are identified with the
components of a gauge field along compactified extra dimensions. We present a
six dimensional model with gauge group U(3)xU(3) and quarks and leptons
accomodated in fundamental and bi-fundamental representations. The model can be
embedded in a D-brane configuration of type I string theory and, upon
compactification on a T^2/Z_2 orbifold, it gives rise to the standard model
with two Higgs doublets.Comment: 28 pages, 4 figures, uses axodraw. Some typos corrected and
references rearrange
Wilson Fermions and Axion Electrodynamics in Optical Lattices
The formulation of massless relativistic fermions in lattice gauge theories
is hampered by the fundamental problem of species doubling, namely, the rise of
spurious fermions modifying the underlying physics. A suitable tailoring of the
fermion masses prevents such abundance of species, and leads to the so-called
Wilson fermions. Here we show that ultracold atoms provide us with the first
controllable realization of these paradigmatic fermions, thus generating a
quantum simulator of fermionic lattice gauge theories. We describe a novel
scheme that exploits laser-assisted tunneling in a cubic optical superlattice
to design the Wilson fermion masses. The high versatility of this proposal
allows us to explore a variety of interesting phases in three-dimensional
topological insulators, and to test the remarkable predictions of axion
electrodynamics.Comment: RevTex4 file, color figures, slightly longer than the published
versio
Engineering Time-Reversal Invariant Topological Insulators With Ultra-Cold Atoms
Topological insulators are a broad class of unconventional materials that are
insulating in the interior but conduct along the edges. This edge transport is
topologically protected and dissipationless. Until recently, all existing
topological insulators, known as quantum Hall states, violated time-reversal
symmetry. However, the discovery of the quantum spin Hall effect demonstrated
the existence of novel topological states not rooted in time-reversal
violations. Here, we lay out an experiment to realize time-reversal topological
insulators in ultra-cold atomic gases subjected to synthetic gauge fields in
the near-field of an atom-chip. In particular, we introduce a feasible scheme
to engineer sharp boundaries where the "edge states" are localized. Besides,
this multi-band system has a large parameter space exhibiting a variety of
quantum phase transitions between topological and normal insulating phases. Due
to their unprecedented controllability, cold-atom systems are ideally suited to
realize topological states of matter and drive the development of topological
quantum computing.Comment: 11 pages, 6 figure
Searching for solar siblings among the HARPS data
The search for the solar siblings has been particularly fruitful in the last
few years. Until now, there are four plausible candidates pointed out in the
literature: HIP21158, HIP87382, HIP47399, and HIP92831. In this study we
conduct a search for solar siblings among the HARPS high-resolution FGK dwarfs
sample, which includes precise chemical abundances and kinematics for 1111
stars. Using a new approach based on chemical abundance trends with the
condensation temperature, kinematics, and ages we found one (additional)
potential solar sibling candidate: HIP97507.Comment: 4 pages, 2 figures, 1 table. Accepted in A&
Anomalous U(1)_A and Electroweak Symmetry Breaking
We suggest a new mechanism for electroweak symmetry breaking in the
supersymmetric Standard Model. Our suggestion is based on the presence of an
anomalous U(1)_A gauge symmetry, which naturally arises in the four dimensional
superstring theory, and heavily relies on the value of the corresponding
Fayet-Illiopoulos \xi-term.Comment: Latex, 11 pages, discussions and references adde
Non-relativistic limit in the 2+1 Dirac Oscillator: A Ramsey Interferometry Effect
We study the non-relativistic limit of a paradigmatic model in Relativistic
Quantum Mechanics, the two-dimensional Dirac oscillator. Remarkably, we find a
novel kind of Zitterbewegung which persists in this non-relativistic regime,
and leads to an observable deformation of the particle orbit. This effect can
be interpreted in terms of a Ramsey Interferometric phenomenon, allowing an
insightful connection between Relativistic Quantum Mechanics and Quantum
Optics. Furthermore, subsequent corrections to the non-relativistic limit,
which account for the usual spin-orbit Zitterbewegung, can be neatly understood
in terms of a Mach-Zehnder interferometer.Comment: RevTex4 file, color figures, submitted for publicatio
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