1,114 research outputs found
New Global F-theory GUTs with U(1) symmetries
We construct global F-theory GUTs with SU(5) x U(1) gauge group defined by
specifying a fully resolved Calabi-Yau fourfold and consistent four-form
G-flux. Its specific U(1) charged matter spectrum allows the desired Yukawa
couplings, but forbids dangerous proton decay operators. The model we find: (1)
does not follow from an underlying higgsed E8 gauge group (2) leaves the class
of theories that can be analyzed with current split-spectral cover techniques.
This avoids recently proposed no-go theorems for models with hypercharge flux,
as required to break the GUT group. The appearance of additional fields is
related geometrically to considering a more general class of sections and 4-1
splits. We show explicitly that the four-dimensional chiral matter index can
still be computed using three-dimensional one-loop Chern-Simons terms.Comment: 24 pages, 2 figure
Complete Intersection Fibers in F-Theory
Global F-theory compactifications whose fibers are realized as complete
intersections form a richer set of models than just hypersurfaces. The detailed
study of the physics associated with such geometries depends crucially on being
able to put the elliptic fiber into Weierstrass form. While such a
transformation is always guaranteed to exist, its explicit form is only known
in a few special cases. We present a general algorithm for computing the
Weierstrass form of elliptic curves defined as complete intersections of
different codimensions and use it to solve all cases of complete intersections
of two equations in an ambient toric variety. Using this result, we determine
the toric Mordell-Weil groups of all 3134 nef partitions obtained from the 4319
three-dimensional reflexive polytopes and find new groups that do not exist for
toric hypersurfaces. As an application, we construct several models that cannot
be realized as toric hypersurfaces, such as the first toric SU(5) GUT model in
the literature with distinctly charged 10 representations and an F-theory model
with discrete gauge group Z_4 whose dual fiber has a Mordell-Weil group with
Z_4 torsion.Comment: 41 pages, 4 figures and 18 tables; added references in v
Relativistic ionization-rescattering with tailored laser pulses
The interaction of relativistically strong tailored laser pulses with an
atomic system is considered. Due to a special tailoring of the laser pulse, the
suppression of the relativistic drift of the ionized electron and a dramatic
enhancement of the rescattering probability is shown to be achievable. The high
harmonic generation rate in the relativistic regime is calculated and shown to
be increased by several orders of magnitude compared to the case of
conventional laser pulses. The energies of the revisiting electron at the
atomic core can approach the MeV domain, thus rendering hard x-ray harmonics
and nuclear reactions with single atoms feasible
Two-mode single-atom laser as a source of entangled light
A two-mode single-atom laser is considered, with the aim of generating
entanglement in macroscopic light. Two transitions in the four-level gain
medium atom independently interact with the two cavity modes, while two other
transitions are driven by control laser fields. Atomic relaxation as well as
cavity losses are taken into account. We show that this system is a source of
macroscopic entangled light over a wide range of control parameters and initial
states of the cavity field
Nuclear signatures in high-harmonic generation from laser-driven muonic atoms
High-harmonic generation from muonic atoms exposed to intense laser fields is
considered. Our particular interest lies in effects arising from the finite
nuclear mass and size. We numerically perform a fully quantum mechanical
treatment of the muon-nucleus dynamics by employing modified soft-core and
hard-core potentials. It is shown that the position of the high-energy cutoff
of the harmonic spectrum depends on the nuclear mass, while the height of the
spectral plateau is sensitive to the nuclear radius. We also demonstrate that
-ray harmonics can be generated from muonic atoms in ultrastrong VUV
fields, which have potential to induce photo-nuclear reactions.Comment: 5 pages, 3 figure
Nuclear quantum optics with x-ray laser pulses
The direct interaction of nuclei with super-intense laser fields is studied.
We show that present and upcoming high-frequency laser facilities, especially
together with a moderate acceleration of the target nuclei, do allow for
resonant laser-nucleus interaction. These direct interactions may be utilized
for the optical measurement of nuclear properties such as the transition
frequency and the dipole moment, thus opening the field of nuclear quantum
optics. As ultimate goal, one may hope that direct laser-nucleus interactions
could become a versatile tool to enhance preparation, control and detection in
nuclear physics.Comment: 5 pages, 3 eps figures, revised versio
A Novel Sequence-Based Antigenic Distance Measure for H1N1, with Application to Vaccine Effectiveness and the Selection of Vaccine Strains
H1N1 influenza causes substantial seasonal illness and was the subtype of the
2009 influenza pandemic. Precise measures of antigenic distance between the
vaccine and circulating virus strains help researchers design influenza
vaccines with high vaccine effectiveness. We here introduce a sequence-based
method to predict vaccine effectiveness in humans. Historical epidemiological
data show that this sequence-based method is as predictive of vaccine
effectiveness as hemagglutination inhibition (HI) assay data from ferret animal
model studies. Interestingly, the expected vaccine effectiveness is greater
against H1N1 than H3N2, suggesting a stronger immune response against H1N1 than
H3N2. The evolution rate of hemagglutinin in H1N1 is also shown to be greater
than that in H3N2, presumably due to greater immune selection pressure.Comment: 26 pages, 7 figures, 2 tables, supplemen
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