561 research outputs found
Heterotic Models from Vector Bundles on Toric Calabi-Yau Manifolds
We systematically approach the construction of heterotic E_8 X E_8 Calabi-Yau
models, based on compact Calabi-Yau three-folds arising from toric geometry and
vector bundles on these manifolds. We focus on a simple class of 101 such
three-folds with smooth ambient spaces, on which we perform an exhaustive scan
and find all positive monad bundles with SU(N), N=3,4,5 structure groups,
subject to the heterotic anomaly cancellation constraint. We find that
anomaly-free positive monads exist on only 11 of these toric three-folds with a
total number of bundles of about 2000. Only 21 of these models, all of them on
three-folds realizable as hypersurfaces in products of projective spaces, allow
for three families of quarks and leptons. We also perform a preliminary scan
over the much larger class of semi-positive monads which leads to about 44000
bundles with 280 of them satisfying the three-family constraint. These 280
models provide a starting point for heterotic model building based on toric
three-folds.Comment: 41 pages, 5 figures. A table modified and a table adde
Heterotic Compactification, An Algorithmic Approach
We approach string phenomenology from the perspective of computational
algebraic geometry, by providing new and efficient techniques for proving
stability and calculating particle spectra in heterotic compactifications. This
is done in the context of complete intersection Calabi-Yau manifolds in a
single projective space where we classify positive monad bundles. Using a
combination of analytic methods and computer algebra we prove stability for all
such bundles and compute the complete particle spectrum, including gauge
singlets. In particular, we find that the number of anti-generations vanishes
for all our bundles and that the spectrum is manifestly moduli-dependent.Comment: 36 pages, Late
Cosmological spacetimes balanced by a scale covariant scalar field
A scale invariant, Weyl geometric, Lagrangian approach to cosmology is
explored, with a a scalar field phi of (scale) weight -1 as a crucial
ingredient besides classical matter \cite{Tann:Diss,Drechsler:Higgs}. For a
particularly simple class of Weyl geometric models (called {\em Einstein-Weyl
universes}) the Klein-Gordon equation for phi is explicitly solvable. In this
case the energy-stress tensor of the scalar field consists of a vacuum-like
term Lambda g_{mu nu} with variable coefficient Lambda, depending on matter
density and spacetime geometry, and of a dark matter like term. Under certain
assumptions on parameter constellations, the energy-stress tensor of the
phi-field keeps Einstein-Weyl universes in locally stable equilibrium. A short
glance at observational data, in particular supernovae Ia (Riess ea 2007),
shows interesting empirical properties of these models.Comment: 28 pages, 1 figure, accepted by Foundations of Physic
Chemical-potential standard for atomic Bose-Einstein condensates
When subject to an external time periodic perturbation of frequency , a
Josephson-coupled two-state Bose-Einstein condensate responds with a constant
chemical potential difference , where is Planck's constant
and is an integer. We propose an experimental procedure to produce
ac-driven atomic Josephson devices that may be used to define a standard of
chemical potential. We investigate how to circumvent some of the specific
problems derived from the present lack of advanced atom circuit technology. We
include the effect of dissipation due to quasiparticles, which is essential to
help the system relax towards the exact Shapiro resonance, and set limits to
the range of values which the various physical quantities must have in order to
achieve a stable and accurate chemical potential difference between the
macroscopic condensates.Comment: 13 pages, 4 figure
Single Spin Superconductivity: Formulation and Ginzburg-Landau Theory
We describe a novel superconducting phase that arises due to a pairing
instability of the half-metallic antiferromagnetic (HM AFM) normal state. This
single spin superconducting (SSS) phase contains broken time reversal symmetry
in addition to broken gauge symmetry, the former due to the underlying magnetic
order in the normal state. A classification of normal state symmetries leads to
the conclusion that the HM AFM normal phase whose point group contains the
inversion operator contains the least symmetry possible which still allows for
a zero momentum pairing instability. The Ginzburg-Landau free energy for the
superconducting order parameter is constructed consistent with the symmetry of
the normal phase, electromagnetic gauge invariance and the crystallographic
point group symmetry including inversion. For cubic, hexagonal and tetragonal
point groups, the possible symmetries of the superconducting phase are
classified, and the free energy is used to construct a generalized phase
diagram. We identify the leading candidate out of the possible SSS phases for
each point group. The symmetry of the superconducting phase is used to
determine the cases where the gap function has generic zeros (point or line
nodes) on the Fermi surface. Such nodes always occur, hence thermodynamic
properties will have power-law behavior at low temperature.Comment: 39 pages, RevTeX, 4 PostScript figures included, submitted to Phys.
Rev.
Late-time H/He-poor circumstellar interaction in the normal-looking type-Ic supernova SN 2021ocs: an exposed oxygen-magnesium layer and extreme stripping of the progenitor
Supernova (SN) 2021ocs was discovered in the galaxy NGC 7828 within the
interacting system Arp 144, and subsequently classified as a normal type-Ic SN
around peak brightness. VLT/FORS2 observations in the nebular phase at 150 d
reveal that the spectrum is dominated by oxygen and magnesium emission lines of
different transitions and ionization states: O I, [O I], [O II], [O III], Mg I,
and Mg II. Such a spectrum has no counterpart in the literature, though it
bears a few features similar to those of some interacting type Ibn and Icn SNe.
Additionally, SN 2021ocs showed a blue color, mag, after
the peak, atypical for a type-Ic SN. Together with the nebular spectrum, this
suggests that SN 2021ocs underwent late-time interaction with an H/He-poor
circumstellar medium (CSM), resulting from the pre-SN progenitor mass loss
during its final 1000 days. The strong O and Mg lines and the absence of
strong C and He lines suggest that the progenitor star's O-Mg layer is exposed,
which places SN 2021ocs as the most extreme case of massive progenitor star's
envelope stripping in interacting SNe, followed by type-Icn (stripped C-O
layer) and Ibn (stripped He-rich layer) SNe. This is the first time such case
is reported in the literature. SN 2021ocs emphasizes the importance of
late-time spectroscopy of even seemingly normal SNe, which reveals the inner
ejecta and progenitor star's mass loss history.Comment: 9 pages, 5 figures, submitte
Reference frames, superselection rules, and quantum information
Recently, there has been much interest in a new kind of ``unspeakable''
quantum information that stands to regular quantum information in the same way
that a direction in space or a moment in time stands to a classical bit string:
the former can only be encoded using particular degrees of freedom while the
latter are indifferent to the physical nature of the information carriers. The
problem of correlating distant reference frames, of which aligning Cartesian
axes and synchronizing clocks are important instances, is an example of a task
that requires the exchange of unspeakable information and for which it is
interesting to determine the fundamental quantum limit of efficiency. There
have also been many investigations into the information theory that is
appropriate for parties that lack reference frames or that lack correlation
between their reference frames, restrictions that result in global and local
superselection rules. In the presence of these, quantum unspeakable information
becomes a new kind of resource that can be manipulated, depleted, quantified,
etcetera. Methods have also been developed to contend with these restrictions
using relational encodings, particularly in the context of computation,
cryptography, communication, and the manipulation of entanglement. This article
reviews the role of reference frames and superselection rules in the theory of
quantum information processing.Comment: 55 pages, published versio
Leptonic and Semileptonic Decays of Charm and Bottom Hadrons
We review the experimental measurements and theoretical descriptions of
leptonic and semileptonic decays of particles containing a single heavy quark,
either charm or bottom. Measurements of bottom semileptonic decays are used to
determine the magnitudes of two fundamental parameters of the standard model,
the Cabibbo-Kobayashi-Maskawa matrix elements and . These
parameters are connected with the physics of quark flavor and mass, and they
have important implications for the breakdown of CP symmetry. To extract
precise values of and from measurements, however,
requires a good understanding of the decay dynamics. Measurements of both charm
and bottom decay distributions provide information on the interactions
governing these processes. The underlying weak transition in each case is
relatively simple, but the strong interactions that bind the quarks into
hadrons introduce complications. We also discuss new theoretical approaches,
especially heavy-quark effective theory and lattice QCD, which are providing
insights and predictions now being tested by experiment. An international
effort at many laboratories will rapidly advance knowledge of this physics
during the next decade.Comment: This review article will be published in Reviews of Modern Physics in
the fall, 1995. This file contains only the abstract and the table of
contents. The full 168-page document including 47 figures is available at
http://charm.physics.ucsb.edu/papers/slrevtex.p
The luminous type Ia supernova 2022ilv and its early excess emission
We present observations and analysis of the host-less and luminous type Ia
supernova 2022ilv, illustrating it is part of the 2003fg-like family, often
referred to as super-Chandrasekhar (Ia-SC) explosions. The ATLAS light curve
shows evidence of a short-lived, pulse-like early excess, similar to that
detected in another luminous type Ia supernova (SN 2020hvf). The light curve is
broad and the early spectra are remarkably similar to SN 2009dc. Adopting a
redshift of for SN 2022ilv based on spectral matching, our
model light curve requires a large Ni mass in the range
M, and a large ejecta mass in the range M. The
early excess can be explained by fast-moving SN ejecta interacting with a thin,
dense shell of circumstellar material close to the progenitor (
cm), a few hours after the explosion. This may be realised in a
double-degenerate scenario, wherein a white dwarf merger is preceded by
ejection of a small amount ( M) of hydrogen and
helium-poor tidally stripped material. A deep pre-explosion Pan-STARRS1 stack
indicates no host galaxy to a limiting magnitude of . This implies
a surprisingly faint limit for any host of , providing further
evidence that these types of explosion occur predominantly in low-metallicity
environments.Comment: Accepted to ApJL after minor revisio
First Observation of
We report on a study of exclusive radiative decays of the Upsilon(1S)
resonance collected with the CLEO-II detector operating at CESR. We present the
first observation of the radiative decays Upsilon(1S)->gamma pi+pi- and
Upsilon(1S)->gamma pi0pi0. For the dipion mass regime m(pipi)>1.0 GeV, we
obtain Br(Upsilon(1S)->gamma pi+pi-=(6.3+/-1.2+/-1.3) x 10^(-5), and
Br(Upsilon(1S)->gamma pi0pi0=(1.7+/-0.6+/-0.3) x 10^(-5). The observed gamma
pipi events are consistent with the hypothesis Upsilon(1S)->gamma f2(1270).Comment: 9 pages, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
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