671 research outputs found
A Matrix Integral Solution to [P,Q]=P and Matrix Laplace Transforms
In this paper we solve the following problems: (i) find two differential
operators P and Q satisfying [P,Q]=P, where P flows according to the KP
hierarchy \partial P/\partial t_n = [(P^{n/p})_+,P], with p := \ord P\ge 2;
(ii) find a matrix integral representation for the associated \t au-function.
First we construct an infinite dimensional space {\cal W}=\Span_\BC
\{\psi_0(z),\psi_1(z),... \} of functions of z\in\BC invariant under the action
of two operators, multiplication by z^p and A_c:= z \partial/\partial z - z +
c. This requirement is satisfied, for arbitrary p, if \psi_0 is a certain
function generalizing the classical H\"ankel function (for p=2); our
representation of the generalized H\"ankel function as a double Laplace
transform of a simple function, which was unknown even for the p=2 case,
enables us to represent the \tau-function associated with the KP time evolution
of the space \cal W as a ``double matrix Laplace transform'' in two different
ways. One representation involves an integration over the space of matrices
whose spectrum belongs to a wedge-shaped contour \gamma := \gamma^+ + \gamma^-
\subset\BC defined by \gamma^\pm=\BR_+\E^{\pm\pi\I/p}. The new integrals above
relate to the matrix Laplace transforms, in contrast with the matrix Fourier
transforms, which generalize the Kontsevich integrals and solve the operator
equation [P,Q]=1.Comment: 27 pages, LaTeX, 1 figure in PostScrip
On the pion electroproduction amplitude
We analyze amplitudes for the pion electroproduction on proton derived from
Lagrangians based on the local chiral SU(2) x SU(2) symmetries. We show that
such amplitudes do contain information on the nucleon axial form factor F_A in
both soft and hard pion regimes. This result invalidates recent Haberzettl's
claim that the pion electroproduction at threshold cannot be used to extract
any information regarding F_A.Comment: 14 pages, 6 figures, revised version, accepted for publication in
Phys. Rev.
Search for light pseudoscalar sgoldstino in K- decays
A search for the light pseudoscalar sgoldstino production in the three body
K- decay K-->pipi0P has been performed with the ISTRA+ detector exposed to the
25 GeV negative secondary beam of the U70 proton synchrotron. No signal is
seen. An upper limit for the branching ratio Br(K->pipi0P), at 90% confidence
level, is found to be around 9*10**-6 in the effective mass m(P) range from 0
till 200 MeV, excluding the region near m(pi0) where it degrades to 3.5*10**-5.Comment: 10 pages, LATEX, 8 EPS figures, revised version, to be published in
Phys.Lett.
Measurement of direct photon emission in decay using stopped positive kaons
The radiative decay () has
been measured with stopped positive kaons. A sample
containing 4k events was analyzed, and the branching ratio
of the direct photon emission process was determined to be . No interference pattern with internal
bremsstrahlung was observed.Comment: 12 pages, 6 figures, 2 tables, to be published in Phys. Lett.
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Detection of antiskyrmions by topological Hall effect in Heusler compounds
Heusler compounds having D2d crystal symmetry gained much attention recently due to the stabilization of a vortexlike spin texture called antiskyrmions in thin lamellae of Mn1.4Pt0.9Pd0.1Sn as reported in the work of Nayak et al. [Nature (London) 548, 561 (2017)10.1038/nature23466]. Here we show that bulk Mn1.4Pt0.9Pd0.1Sn undergoes a spin-reorientation transition from a collinear ferromagnetic to a noncollinear configuration of Mn moments below 135 K, which is accompanied by the emergence of a topological Hall effect. We tune the topological Hall effect in Pd and Rh substituted Mn1.4PtSn Heusler compounds by changing the intrinsic magnetic properties and spin textures. A unique feature of the present system is the observation of a zero-field topological Hall resistivity with a sign change which indicates the robust formation of antiskyrmions. © 2020 authors. Published by the American Physical Society
The future of sovereignty in multilevel governance Europe: a constructivist reading
Multilevel governance presents a depiction of contemporary structures in EU Europe as consisting of overlapping authorities and competing competencies. By focusing on emerging non-anarchical structures in the international system, hence moving beyond the conventional hierarchy/anarchy dichotomy to distinguish domestic and international arenas, this seems a radical transformation of the familiar Westphalian system and to undermine state sovereignty. Paradoxically, however, the principle of sovereignty proves to be resilient despite its alleged empirical decline. This article argues that social constructivism can explain the paradox, by considering sovereign statehood as a process-dependent institutional fact, and by showing that multilevel governance can feed into this process
Final-State Phases in , and Decays
The final-state phases in , and decays
appear to follow a pattern similar to those in , , and decays. Each set of processes is characterized by
three charge states but only two independent amplitudes, so the amplitudes form
triangles in the complex plane. For the first two sets the triangles appear to
have non-zero area, while for the or decays the areas
of the triangles are consistent with zero. Following an earlier discussion of
this behavior for decays, a similar analysis is performed for B decays, and
the relative phases and magnitudes of contributing amplitudes are determined.
The significance of recent results on \ob \to D^{(*)0} \bar{K}^{(*)0} is
noted. Open theoretical and experimental questions are indicated.Comment: 16 pages, LaTeX, 3 figures, to be submitted to Phys. Rev. D.
References added; comments on new experimental results and analysi
Poisson-Lie group of pseudodifferential symbols
We introduce a Lie bialgebra structure on the central extension of the Lie
algebra of differential operators on the line and the circle (with scalar or
matrix coefficients). This defines a Poisson--Lie structure on the dual group
of pseudodifferential symbols of an arbitrary real (or complex) order. We show
that the usual (second) Benney, KdV (or GL_n--Adler--Gelfand--Dickey) and KP
Poisson structures are naturally realized as restrictions of this Poisson
structure to submanifolds of this ``universal'' Poisson--Lie group.
Moreover, the reduced (=SL_n) versions of these manifolds (W_n-algebras in
physical terminology) can be viewed as subspaces of the quotient (or Poisson
reduction) of this Poisson--Lie group by the dressing action of the group of
functions.
Finally, we define an infinite set of functions in involution on the
Poisson--Lie group that give the standard families of Hamiltonians when
restricted to the submanifolds mentioned above. The Poisson structure and
Hamiltonians on the whole group interpolate between the Poisson structures and
Hamiltonians of Benney, KP and KdV flows. We also discuss the geometrical
meaning of W_\infty as a limit of Poisson algebras W_\epsilon as \epsilon goes
to 0.Comment: 64 pages, no figure
Strong laser fields as a probe for fundamental physics
Upcoming high-intensity laser systems will be able to probe the
quantum-induced nonlinear regime of electrodynamics. So far unobserved QED
phenomena such as the discovery of a nonlinear response of the quantum vacuum
to macroscopic electromagnetic fields can become accessible. In addition, such
laser systems provide for a flexible tool for investigating fundamental
physics. Primary goals consist in verifying so far unobserved QED phenomena.
Moreover, strong-field experiments can search for new light but weakly
interacting degrees of freedom and are thus complementary to accelerator-driven
experiments. I review recent developments in this field, focusing on photon
experiments in strong electromagnetic fields. The interaction of
particle-physics candidates with photons and external fields can be
parameterized by low-energy effective actions and typically predict
characteristic optical signatures. I perform first estimates of the accessible
new-physics parameter space of high-intensity laser facilities such as POLARIS
and ELI.Comment: 7 pages, Key Lecture at the ELI Workshop and School on "Fundamental
Physics with Ultra-High Fields", 9 September - 2 October 2008 at Frauenworth
Monastery, German
Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration
Extensive experimental data from high-energy nucleus-nucleus collisions were
recorded using the PHENIX detector at the Relativistic Heavy Ion Collider
(RHIC). The comprehensive set of measurements from the first three years of
RHIC operation includes charged particle multiplicities, transverse energy,
yield ratios and spectra of identified hadrons in a wide range of transverse
momenta (p_T), elliptic flow, two-particle correlations, non-statistical
fluctuations, and suppression of particle production at high p_T. The results
are examined with an emphasis on implications for the formation of a new state
of dense matter. We find that the state of matter created at RHIC cannot be
described in terms of ordinary color neutral hadrons.Comment: 510 authors, 127 pages text, 56 figures, 1 tables, LaTeX. Submitted
to Nuclear Physics A as a regular article; v3 has minor changes in response
to referee comments. Plain text data tables for the points plotted in figures
for this and previous PHENIX publications are (or will be) publicly available
at http://www.phenix.bnl.gov/papers.htm
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