803 research outputs found
Competition between fluctuations and disorder in frustrated magnets
We investigate the effects of impurities on the nature of the phase
transition in frustrated magnets, in d=4-epsilon dimensions. For sufficiently
small values of the number of spin components, we find no physically relevant
stable fixed point in the deep perturbative region (epsilon << 1), contrarily
to what is to be expected on very general grounds. This signals the onset of
important physical effects.Comment: 4 pages, 3 figures, published versio
ADHM/Nahm Construction of Localized Solitons in Noncommutative Gauge Theories
We study the relationship between ADHM/Nahm construction and ``solution
generating technique'' of BPS solitons in noncommutative gauge theories.
ADHM/Nahm construction and ``solution generating technique'' are the most
strong ways to construct exact BPS solitons. Localized solitons are the
solitons which are generated by the ``solution generating technique.'' The
shift operators which play crucial roles in ``solution generating technique''
naturally appear in ADHM/Nahm construction and we can construct various exact
localized solitons including new solitons: localized periodic instantons
(=localized calorons) and localized doubly-periodic instantons. Nahm
construction also gives rise to BPS fluxons straightforwardly from the
appropriate input Nahm data which is expected from the D-brane picture of BPS
fluxons. We also show that the Fourier-transformed soliton of the localized
caloron in the zero-period limit exactly coincides with the BPS fluxon.Comment: 30 pages, LaTeX, 3 figures; v3: minor changes, references added; v4:
references added, version to appear in PR
Spinning particles in Taub-NUT space
The geodesic motion of pseudo-classical spinning particles in Euclidean
Taub-NUT space is analysed. The constants of motion are expressed in terms of
Killing-Yano tensors. Some previous results from the literature are corrected.Comment: LaTeX, 8 page
SU(2) Calorons and Magnetic Monopoles
We investigate the self-dual Yang-Mills gauge configurations on when the gauge symmetry SU(2) is broken to U(1) by the Wilson loop. We
construct the explicit field configuration for a single instanton by the Nahm
method and show that an instanton is composed of two self-dual monopoles of
opposite magnetic charge. We normalize the moduli space metric of an instanton
and study various limits of the field configuration and its moduli space
metric.Comment: 17 pages, RevTex, 1 Figur
Sex differences in neurodevelopmental and common mental disorders examined from three epidemiological perspectives.
Sex differences in neurodevelopmental and common mental disorders are a ubiquitous, well-known, though poorly understood phenomenon. This study examined the issue from three epidemiological perspectives: congruence in age of onset, distribution of sex-ratios with respect to age of onset and similarity of comorbidity and risk factor patterns. The analysis was based on data from the population-based PsyCoLaus study (N = 4874, age 35-82 y). Congruence in age of onset and distribution of sex-ratios were examined with the Mann-Whitney test and cluster analysis. The similarity of comorbidity and risk factor patterns, which were represented by 35 variables, was assessed with the Jaccard coefficient and, after factor analysis, with Tucker's congruence coefficient. While age of onset parameters differed little by sex, the sex ratio varied markedly both in early and in late onset disorders. Moreover, the Jaccard coefficients for most disorders indicated that the similarity of comorbidity and further association patterns was low. Similarly, Tucker's congruence coefficient remained below the range of fair similarity in all factor combinations. In sum, sex differences in common mental disorders were impressively reflected by diverging sex ratios and comorbidity / risk factor patterns. This outcome supports the notion that most mental disorders need a sex-specific etiopathogenetic understanding
Hamiltonian dynamics and spectral theory for spin-oscillators
We study the Hamiltonian dynamics and spectral theory of spin-oscillators.
Because of their rich structure, spin-oscillators display fairly general
properties of integrable systems with two degrees of freedom. Spin-oscillators
have infinitely many transversally elliptic singularities, exactly one
elliptic-elliptic singularity and one focus-focus singularity. The most
interesting dynamical features of integrable systems, and in particular of
spin-oscillators, are encoded in their singularities. In the first part of the
paper we study the symplectic dynamics around the focus-focus singularity. In
the second part of the paper we quantize the coupled spin-oscillators systems
and study their spectral theory. The paper combines techniques from
semiclassical analysis with differential geometric methods.Comment: 32 page
Constructing Self-Dual Strings
We present an ADHMN-like construction which generates self-dual string
solutions to the effective M5-brane worldvolume theory from solutions to the
Basu-Harvey equation. Our construction finds a natural interpretation in terms
of gerbes, which we develop in some detail. We also comment on a possible
extension to stacks of multiple M5-branes.Comment: 1+19 pages, presentation improved, minor corrections, published
versio
D0-D4 brane tachyon condensation to a BPS state and its excitation spectrum in noncommutative super Yang-Mills theory
We investigate the D0-D4-brane system for different B-field backgrounds
including the small instanton singularity in noncommutative SYM theory. We
discuss the excitation spectrum of the unstable state as well as for the BPS
D0-D4 bound state. We compute the tachyon potential which reproduces the
complete mass defect. The relevant degrees of freedom are the massless (4,4)
strings. Both results are in contrast with existing string field theory
calculations. The excitation spectrum of the small instanton is found to be
equal to the excitation spectrum of the fluxon solution on R^2_theta x R which
we trace back to T-duality. For the effective theory of the (0,0) string
excitations we obtain a BFSS matrix model. The number of states in the
instanton background changes significantly when the B-field becomes self-dual.
This leads us to the proposal of the existence of a phase transition or cross
over at self-dual B-field.Comment: a4 11pt Latex2e 40 pages; v2: typos fixed, refined comments on
renormalisation, refs added, v3: ref added, version publishe
Four dimensional "old minimal" N=2 supersymmetrization of R^4
We write in superspace the lagrangian containing the fourth power of the Weyl
tensor in the "old minimal" d=4, N=2 supergravity, without local SO(2)
symmetry. Using gauge completion, we analyze the lagrangian in components. We
find out that the auxiliary fields which belong to the Weyl and compensating
vector multiplets have derivative terms and therefore cannot be eliminated
on-shell. Only the auxiliary fields which belong to the compensating nonlinear
multiplet do not get derivatives and could still be eliminated; we check that
this is possible in the leading terms of the lagrangian. We compare this result
to the similar one of "old minimal" N=1 supergravity and we comment on possible
generalizations to other versions of N=1,2 supergravity.Comment: 31 pages, no figures. Minor corrections. Details of the full
calculation included as an appendix. Reference adde
Liquid-gas phase transition in hot nuclei studied with INDRA
Thanks to the high detection quality of the INDRA array, signatures related
to the dynamics (spinodal decomposition) and thermodynamics (negative
microcanonical heat capacity) of a liquid-gas phase transition have been
simultaneously studied in multifragmentation events in the Fermi energy domain.
The correlation between both types of signals strongly supports the existence
of a first order phase transition for hot nuclei.Comment: 9 pages, 2 figures, Invited talk to Nucleus-nucleus 2003 Moscow June
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