909 research outputs found
Towards an explicit expression of the Seiberg-Witten map at all orders
The Seiberg-Witten map links noncommutative gauge theories to ordinary gauge
theories, and allows to express the noncommutative variables in terms of the
commutative ones. Its explicit form can be found order by order in the
noncommutative parameter theta and the gauge potential A by the requirement
that gauge orbits are mapped on gauge orbits. This of course leaves
ambiguities, corresponding to gauge transformations, and there is an infinity
of solutions. Is there one better, clearer than the others ? In the abelian
case, we were able to find a solution, linked by a gauge transformation to
already known formulas, which has the property of admitting a recursive
formulation, uncovering some pattern in the map. In the special case of a pure
gauge, both abelian and non-abelian, these expressions can be summed up, and
the transformation is expressed using the parametrisation in terms of the gauge
group.Comment: 17 pages. Latex, 1 figure. v2: minor changes, published versio
Non-Commutative Instantons and the Seiberg-Witten Map
We present several results concerning non-commutative instantons and the
Seiberg-Witten map. Using a simple ansatz we find a large new class of
instanton solutions in arbitrary even dimensional non-commutative Yang-Mills
theory. These include the two dimensional ``shift operator'' solutions and the
four dimensional Nekrasov-Schwarz instantons as special cases. We also study
how the Seiberg-Witten map acts on these instanton solutions. The infinitesimal
Seiberg-Witten map is shown to take a very simple form in operator language,
and this result is used to give a commutative description of non-commutative
instantons. The instanton is found to be singular in commutative variables.Comment: 26 pages, AMS-LaTeX. v2: the formula for the commutative description
of the Nekrasov-Schwarz instanton corrected (sec. 4). v3: minor correction
The Seiberg-Witten Map for a Time-dependent Background
In this paper the Seiberg-Witten map for a time-dependent background related
to a null-brane orbifold is studied. The commutation relations of the
coordinates are linear, i.e. it is an example of the Lie algebra type. The
equivalence map between the Kontsevich star product for this background and the
Weyl-Moyal star product for a background with constant noncommutativity
parameter is also studied.Comment: latex, 13 pages, references added and some misprints correcte
Establishing the values for patient engagement (PE) in health-related quality of life (HRQoL) research: an international, multiple-stakeholder perspective
PurposeActive patient engagement is increasingly viewed as essential to ensuring that patient-driven perspectives are considered throughout the research process. However, guidance for patient engagement (PE) in HRQoL research does not exist, the evidence-base for practice is limited, and we know relatively little about underpinning values that can impact on PE practice. This is the first study to explore the values that should underpin PE in contemporary HRQoL research to help inform future good practice guidance. MethodsA modified âWorld CafĂ©â was hosted as a collaborative activity between patient partners, clinicians and researchers: self-nominated conference delegates participated in group discussions to explore values associated with the conduct and consequences of PE. Values were captured via post-it notes and by nominated note-takers. Data were thematically analysed: emergent themes were coded and agreement checked. Association between emergent themes, values and the Public Involvement Impact Assessment Framework were explored. ResultsEighty participants, including 12 patient partners, participated in the 90-min event. Three core values were defined: (1) building relationships; (2) improving research quality and impact; and (3) developing best practice. Participants valued the importance of building genuine, collaborative and deliberative relationshipsâunderpinned by honesty, respect, co-learning and equityâand the impact of effective PE on research quality and relevance. Conclusions An explicit statement of values seeks to align all stakeholders on the purpose, practice and credibility of PE activities. An innovative, flexible and transparent research environment was valued as essential to developing a trustworthy evidence-base with which to underpin future guidance for good PE practice.Peer reviewe
Seiberg-Witten Transforms of Noncommutative Solitons
We evaluate the Seiberg-Witten map for solitons and instantons in
noncommutative gauge theories in various dimensions. We show that solitons
constructed using the projection operators have delta-function supports when
expressed in the commutative variables. This gives a precise identification of
the moduli of these solutions as locations of branes. On the other hand, an
instanton solution in four dimensions allows deformation away from the
projection operator construction. We evaluate the Seiberg-Witten transform of
the U(2) instanton and show that it has a finite size determined by the
noncommutative scale and by the deformation parameter \rho. For large \rho, the
profile of the D0-brane density of the instanton agrees surprisingly well with
that of the BPST instanton on commutative space.Comment: 29 pages, LaTeX; comments added, typos corrected, and a reference
added; comments added, typos correcte
Twisted Bundles on Noncommutative and D-brane Bound States
We construct twisted quantum bundles and adjoint sections on noncommutative
, and investigate relevant D-brane bound states with non-Abelian
backgrounds. We also show that the noncommutative with non-Abelian
backgrounds exhibits SO duality and via this duality we get a Morita
equivalent on which only D0-branes exist. For a reducible non-Abelian
background, the moduli space of D-brane bound states in Type II string theory
takes the form .Comment: 19 pages, Latex. v2: Title is changed. Minor corrections. A reference
adde
Tachyon Condensation on Noncommutative Torus
We discuss noncommutative solitons on a noncommutative torus and their
application to tachyon condensation. In the large B limit, they can be exactly
described by the Powers-Rieffel projection operators known in the mathematical
literature. The resulting soliton spectrum is consistent with T-duality and is
surprisingly interesting. It is shown that an instability arises for any
D-branes, leading to the decay into many smaller D-branes. This phenomenon is
the consequence of the fact that K-homology for type II von Neumann factor is
labeled by R.Comment: LaTeX, 17 pages, 1 figur
A deformation of AdS_5 x S^5
We analyse a one parameter family of supersymmetric solutions of type IIB
supergravity that includes AdS_5 x S^5. For small values of the parameter the
solutions are causally well-behaved, but beyond a critical value closed
timelike curves (CTC's) appear. The solutions are holographically dual to N=4
supersymmetric Yang-Mills theory on a non-conformally flat background with
non-vanishing R-currents. We compute the holographic energy-momentum tensor for
the spacetime and show that it remains finite even when the CTC's appear. The
solutions, as well as the uplift of some recently discovered AdS_5 black hole
solutions, are shown to preserve precisely two supersymmetries.Comment: 16 pages, v2: typos corrected and references adde
Emergent Gravity from Noncommutative Spacetime
We showed before that self-dual electromagnetism in noncommutative (NC)
spacetime is equivalent to self-dual Einstein gravity. This result implies a
striking picture about gravity: Gravity can emerge from electromagnetism in NC
spacetime. Gravity is then a collective phenomenon emerging from gauge fields
living in fuzzy spacetime. We elucidate in some detail why electromagnetism in
NC spacetime should be a theory of gravity. In particular, we show that NC
electromagnetism is realized through the Darboux theorem as a diffeomorphism
symmetry G which is spontaneously broken to symplectomorphism H due to a
background symplectic two-form , giving rise to
NC spacetime. This leads to a natural speculation that the emergent gravity
from NC electromagnetism corresponds to a nonlinear realization G/H of the
diffeomorphism group, more generally its NC deformation. We also find some
evidences that the emergent gravity contains the structure of generalized
complex geometry and NC gravity. To illuminate the emergent gravity, we
illustrate how self-dual NC electromagnetism nicely fits with the twistor space
describing curved self-dual spacetime. We also discuss derivative corrections
of Seiberg-Witten map which give rise to higher order gravity.Comment: 50 pages; Cosmetic revision and updated reference
Black holes in Goedel-type universes with a cosmological constant
We discuss supersymmetric black holes embedded in a Goedel-type universe with
cosmological constant in five dimensions. The spacetime is a fibration over a
four-dimensional Kaehler base manifold, and generically has closed timelike
curves. Asymptotically the space approaches a deformation of AdS_5, which
suggests that the appearance of closed timelike curves should have an
interpretation in some deformation of D=4, N=4 super-Yang-Mills theory.
Finally, a Goedel-de Sitter universe is also presented and its causal structure
is discussed.Comment: 25 pages, Latex, no figures, references updated, physical discussion
of the solutions considerably expanded, holographic stress tensor and
conserved charges of Goedel-AdS(5) solution compute
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