1,936 research outputs found
Hidden symmetries in two dimensional field theory
The bosonization process elegantly shows the equivalence of massless scalar
and fermion fields in two space-time dimensions. However, with multiple
fermions the technique often obscures global symmetries. Witten's non-Abelian
bosonization makes these symmetries explicit, but at the expense of a somewhat
complicated bosonic action. Frenkel and Kac have presented an intricate
mathematical formalism relating the various approaches. Here I reduce these
arguments to the simplest case of a single massless scalar field. In
particular, using only elementary quantum field theory concepts, I expose a
hidden chiral symmetry in this trivial theory. I then
discuss in what sense this field should be interpreted as a Goldstone boson.Comment: 15 pages. Revision adds numerous references and puts things in better
historical contex
The Genetics of the Mood Disorder Spectrum: Genome-wide Association Analyses of More Than 185,000 Cases and 439,000 Controls
Background:
Mood disorders (including major depressive disorder and bipolar disorder) affect 10% to 20% of the population. They range from brief, mild episodes to severe, incapacitating conditions that markedly impact lives. Multiple approaches have shown considerable sharing of risk factors across mood disorders despite their diagnostic distinction.
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Methods:
To clarify the shared molecular genetic basis of major depressive disorder and bipolar disorder and to highlight disorder-specific associations, we meta-analyzed data from the latest Psychiatric Genomics Consortium genome-wide association studies of major depression (including data from 23andMe) and bipolar disorder, and an additional major depressive disorder cohort from UK Biobank (total: 185,285 cases, 439,741 controls; nonoverlapping N = 609,424).
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Results:
Seventy-three loci reached genome-wide significance in the meta-analysis, including 15 that are novel for mood disorders. More loci from the Psychiatric Genomics Consortium analysis of major depression than from that for bipolar disorder reached genome-wide significance. Genetic correlations revealed that type 2 bipolar disorder correlates strongly with recurrent and single-episode major depressive disorder. Systems biology analyses highlight both similarities and differences between the mood disorders, particularly in the mouse brain cell types implicated by the expression patterns of associated genes. The mood disorders also differ in their genetic correlation with educational attainmentâthe relationship is positive in bipolar disorder but negative in major depressive disorder.
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Conclusions:
The mood disorders share several genetic associations, and genetic studies of major depressive disorder and bipolar disorder can be combined effectively to enable the discovery of variants not identified by studying either disorder alone. However, we demonstrate several differences between these disorders. Analyzing subtypes of major depressive disorder and bipolar disorder provides evidence for a genetic mood disorders spectrum
Extended Gauge Theories in Euclidean Space with Higher Spin Fields
The extended Yang-Mills gauge theory in Euclidean space is a renormalizable
(by power counting) gauge theory describing a local interacting theory of
scalar, vector, and tensor gauge fields (with maximum spin 2). In this article
we study the quantum aspects and various generalizations of this model in
Euclidean space. In particular the quantization of the pure gauge model in a
common class of covariant gauges is performed. We generalize the pure gauge
sector by including matter fermions in the adjoint representation of the gauge
group and analyze its N=1 and N=2 supersymmetric extensions. We show that the
maximum half-integer spin contained in these fermion fields in dimension 4 is
3/2. Moreover we develop an extension of this theory so as to include internal
gauge symmetries and the coupling to bosonic matter fields. The spontaneous
symmetry breaking of the extended gauge symmetry is also analyzed.Comment: LaTeX, 36 pages, section 4 expanded, new section 7 and new references
added, to appear in Annals of Physic
Using baryon octet magnetic moments and masses to fix the pion cloud contribution
Using SU(3) symmetry to constrain the pion BB' couplings, assuming SU(3)
breaking comes only from one-loop pion cloud contributions, and using the the
covariant spectator theory to describe the photon coupling to the quark core,
we show how the experimental masses and magnetic moments of the baryon octet
can be used to set a model independent constraint on the strength of the pion
cloud contributions to the octet, and hence the nucleon, form factors at Q2=0.Comment: 7 pages, 1 figur
Pairwise approach for analysis and reporting of childâs free sugars intake from a birth cohort study
Objectives:
The prospective cohort design is an important research design, but a common challenge is missing data. The purpose of this study is to compare three approaches to managing missing data, the pairwise (n = 1386 children), the partial or modified pairwise (n = 1019) and the listwise (n = 546), to characterize the trajectories of children's free sugars intake (FSI) across early childhood.
Methods:
By applying the Group-based Trajectory Model Technique to three waves of data collected from a prospective cohort study of South Australian children, this study examined the three approaches in managing missing data to validate and discuss children's FSI trajectories.
Results:
Each approach identified three distinct trajectories of child's FSI from 1 to 5âyears of age: (1) âlow and fast increasingâ, (2) âmoderate and increasingâ and (3) âhigh and increasingâ. The trajectory memberships were consistent across the three approaches, and were for the pairwise scenario (1) 15.1%, (2) 68.3% and (3) 16.6%; the partial or modified pairwise (1) 15.9%, (2) 64.1% and (3) 20.0%; and the listwise (1) 14.9%, (2) 64.9% and (3) 20.2% of children.
Conclusions:
Given the comparability of the findings across the analytical approaches and the samples' characteristics between baseline and across different data collection waves, it is recommended that the pairwise approach be used in future analyses to optimize the sample size and statistical power when examining the relationship between FSI in the first years of life and health outcome such as dental caries
Constraints, Histones, and the 30 Nanometer Spiral
We investigate the mechanical stability of a segment of DNA wrapped around a
histone in the nucleosome configuration. The assumption underlying this
investigation is that the proper model for this packaging arrangement is that
of an elastic rod that is free to twist and that writhes subject to mechanical
constraints. We find that the number of constraints required to stabilize the
nuclesome configuration is determined by the length of the segment, the number
of times the DNA wraps around the histone spool, and the specific constraints
utilized. While it can be shown that four constraints suffice, in principle, to
insure stability of the nucleosome, a proper choice must be made to guarantee
the effectiveness of this minimal number. The optimal choice of constraints
appears to bear a relation to the existence of a spiral ridge on the surface of
the histone octamer. The particular configuration that we investigate is
related to the 30 nanometer spiral, a higher-order organization of DNA in
chromatin.Comment: ReVTeX, 15 pages, 18 figure
Effective field theory and the quark model
We analyze the connections between the quark model (QM) and the description
of hadrons in the low-momentum limit of heavy-baryon effective field theory in
QCD. By using a three-flavor-index representation for the effective baryon
fields, we show that the ``nonrelativistic'' constituent QM for baryon masses
and moments is completely equivalent through O(m_s) to a parametrization of the
relativistic field theory in a general spin--flavor basis. The flavor and spin
variables can be identified with those of effective valence quarks. Conversely,
the spin-flavor description clarifies the structure and dynamical
interpretation of the chiral expansion in effective field theory, and provides
a direct connection between the field theory and the semirelativistic models
for hadrons used in successful dynamical calculations. This allows dynamical
information to be incorporated directly into the chiral expansion. We find, for
example, that the striking success of the additive QM for baryon magnetic
moments is a consequence of the relative smallness of the non-additive
spin-dependent corrections.Comment: 25 pages, revtex, no figure
Fermion-Boson Duality of One-dimensional Quantum Particles with Generalized Contact Interaction
For a system of spinless one-dimensional fermions, the non-vanishing
short-range limit of two-body interaction is shown to induce the wave-function
discontinuity. We prove the equivalence of this fermionic system and the
bosonic particle system with two-body -function interaction with the
reversed role of strong and weak couplings.
KEYWORDS: one-dimensional system, -interaction, solvable many-body
problem, exact bosonizationComment: 4 pages ReVTeX 4 epsf figures included, new Ref
Vacuum orbit and spontaneous symmetry breaking in hyperbolic sigma models
We present a detailed study of quantized noncompact, nonlinear SO(1,N)
sigma-models in arbitrary space-time dimensions D \geq 2, with the focus on
issues of spontaneous symmetry breaking of boost and rotation elements of the
symmetry group. The models are defined on a lattice both in terms of a transfer
matrix and by an appropriately gauge-fixed Euclidean functional integral. The
main results in all dimensions \geq 2 are: (i) On a finite lattice the systems
have infinitely many nonnormalizable ground states transforming irreducibly
under a nontrivial representation of SO(1,N); (ii) the SO(1,N) symmetry is
spontaneously broken. For D =2 this shows that the systems evade the
Mermin-Wagner theorem. In this case in addition: (iii) Ward identities for the
Noether currents are derived to verify numerically the absence of explicit
symmetry breaking; (iv) numerical results are presented for the two-point
functions of the spin field and the Noether current as well as a new order
parameter; (v) in a large N saddle-point analysis the dynamically generated
squared mass is found to be negative and of order 1/(V \ln V) in the volume,
the 0-component of the spin field diverges as \sqrt{\ln V}, while SO(1,N)
invariant quantities remain finite.Comment: 60 pages, 12 Figures, AMS-Latex; v2: results on vacuum orbit and
spontaneous symmetry breaking extended to all dimension
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