Michael Flohr

Publications

• Correlation Functions in N=3 Superconformal Theory

  Dmitriy Drichel, Michael Flohr

  06/2010;

  Using a superspace representation of the N=3 Neveau-Schwarz super Virasoro algebra, we find solutions of N=3 super Ward identities. Global transformations generated by the non-abelian supercurrent require not only superfields, but also functions of Grassmann variables (in particular correlation func... [more] Using a superspace representation of the N=3 Neveau-Schwarz super Virasoro algebra, we find solutions of N=3 super Ward identities. Global transformations generated by the non-abelian supercurrent require not only superfields, but also functions of Grassmann variables (in particular correlation functions and their linear combinations) to be su(2) representations. As a consequence, the only admissible fields in the theory are isospin singlets and doublets. We show how to compute the generic form of any N=3 n-point function and demonstrate a construction of all su(2) representations on the space of N=3 superfunctions.

• On a Logarithmic Deformation of the Supersymmetric bc-system on Curved Manifolds

  Kirsten Vogeler, Michael Flohr

  02/2009;

  E. Frenkel, A. Losev and N. Nekrasov claim that a certain class of theories on compact Kahler manifolds and in particular the "gauged" supersymmetric bc-system on CP^1 are logarithmic conformal field theories. We discuss that proposition on a classical level for the bc-system on CP^1. The ... [more] E. Frenkel, A. Losev and N. Nekrasov claim that a certain class of theories on compact Kahler manifolds and in particular the "gauged" supersymmetric bc-system on CP^1 are logarithmic conformal field theories. We discuss that proposition on a classical level for the bc-system on CP^1. The outcome of our investigation conforms to their conjecture. The property of being a logarithmic CFT thus can be interpreted as an effect of gravity.

• On Factorization Constraints for Branes in the H3+ Model

  Hendrik Adorf, Michael Flohr

  01/2008;

  We comment on the brane solutions for the boundary H3+ model that have been proposed so far and point out that they should be distinguished according to the patterns regular/irregular and discrete/continuous. In the literature, mostly irregular branes have been studied, while results on the regular ... [more] We comment on the brane solutions for the boundary H3+ model that have been proposed so far and point out that they should be distinguished according to the patterns regular/irregular and discrete/continuous. In the literature, mostly irregular branes have been studied, while results on the regular ones are rare. For all types of branes, there are questions about how a second factorization constraint in the form of a b^{-2}/2-shift equation can be derived. Here, we assume analyticity of the boundary two point function, which means that the Cardy-Lewellen constraints remain unweakened. This enables us to derive unambiguously the desired b^{-2}/2-shift equations. They serve as important additional consistency conditions. For some regular branes, we also derive 1/2-shift equations that were not known previously. Case by case, we discuss possible solutions to the enlarged system of constraints. We find that the well-known irregular continuous AdS_2 branes are consistent with our new factorization constraint. Furthermore, we establish the existence of a new type of brane: The shift equations in a certain regular discrete case possess a non-trivial solution that we write down explicitly. All other types are found to be inconsistent when using our second constraint. We discuss these results in view of the Hosomichi-Ribault proposal and some of our earlier results on the derivation of b^{-2}/2-shift equations. Comment: v2: version published in IJMPA; remark on possible pitfalls when doing the analytic continuations added; discussion of AdS2 vs. S2 branes changed; remarks on the brane spectrum and on the regular branes added; some typos corrected; Ref. Exton: Publisher added; 50 pages

• Towards the Construction of Local Logarithmic Conformal Field Theories

  Anne-Ly Do, Michael Flohr

  11/2007;

  Although logarithmic conformal field theories (LCFTs) are known not to factorise many previous findings have only been formulated on their chiral halves. Making only mild and rather general assumptions on the structure of an chiral LCFT we deduce statements about its local non-chiral equivalent. Two... [more] Although logarithmic conformal field theories (LCFTs) are known not to factorise many previous findings have only been formulated on their chiral halves. Making only mild and rather general assumptions on the structure of an chiral LCFT we deduce statements about its local non-chiral equivalent. Two methods are presented how to construct local representations as subrepresentations of the tensor product of chiral and anti-chiral Jordan cells. Furthermore we explore the assembly of generic non-chiral correlation functions from generic chiral and anti-chiral correlators. The constraint of locality is studied and the generality of our method is discussed.

• Continuously Crossing u=z in the H3+ Boundary CFT

  Hendrik Adorf, Michael Flohr

  08/2007;

  For AdS boundary conditions, we give a solution of the H3+ two point function involving degenerate field with SL(2)-label b^{-2}/2, which is defined on the full (u,z) unit square. It consists of two patches, one for z<u and one for u<z. Along the u=z "singularity", the solutions from... [more] For AdS boundary conditions, we give a solution of the H3+ two point function involving degenerate field with SL(2)-label b^{-2}/2, which is defined on the full (u,z) unit square. It consists of two patches, one for z<u and one for u<z. Along the u=z "singularity", the solutions from both patches are shown to have finite limits and are merged continuously as suggested by the work of Hosomichi and Ribault. From this two point function, we can derive b^{-2}/2-shift equations for AdS_2 D-branes. We show that discrete as well as continuous AdS_2 branes are consistent with our novel shift equations without any new restrictions.

• On Verlinde-Like Formulas in c_{p,1} Logarithmic Conformal Field Theories

  Michael Flohr, Holger Knuth

  06/2007;

  Two different approaches to calculate the fusion rules of the c_{p,1} series of logarithmic conformal field theories are discussed. Both are based on the modular transformation properties of a basis of chiral vacuum torus amplitudes, which contains the characters of the irreducible representations. ... [more] Two different approaches to calculate the fusion rules of the c_{p,1} series of logarithmic conformal field theories are discussed. Both are based on the modular transformation properties of a basis of chiral vacuum torus amplitudes, which contains the characters of the irreducible representations. One of these is an extension, which we develop here for a non-semisimple generalisation of the Verlinde formula introduced by Fuchs et al., to include fusion products with indecomposable representations. The other uses the Verlinde formula in its usual form and gets the fusion coefficients in the limit, in which the basis of torus amplitudes degenerates to the linear dependent set of characters of irreducible and indecomposable representations. We discuss the effects, which this linear dependence has on any result for fusion rules, which are calculated from these character's modular transformation properties. We show that the two presented methods are equivalent. Furthermore we calculate explicit BPZ-like expressions for the resulting fusion rules for all p larger than 2.

• On the Various Types of D-Branes in the Boundary H3+ Model

  Hendrik Adorf, Michael Flohr

  03/2007;

  We comment on the D-brane solutions for the boundary H3+ model that have been proposed so far and point out that many more types of D-branes should be considered possible. We start a systematic derivation of the 1/2- and b^{-2}/2-shift equations corresponding to each type. These equations serve as c... [more] We comment on the D-brane solutions for the boundary H3+ model that have been proposed so far and point out that many more types of D-branes should be considered possible. We start a systematic derivation of the 1/2- and b^{-2}/2-shift equations corresponding to each type. These equations serve as consistency conditions and we discuss their possible solutions. On this basis, we show for the known AdS_2^(d) branes, that only strings transforming in finite dimensional SL(2) representations can couple to them. Moreover, we also demonstrate that strings in the infinite dimensional continuous SL(2) representations do not couple consistently to the known AdS_2 branes. For some other types, we show that no consistent solutions seem to exist at all.

• Fermionic Expressions for the Characters of c(p,1) Logarithmic Conformal Field Theories

  Michael Flohr, Carsten Grabow, Michael Koehn

  12/2006;

  We present fermionic quasi-particle sum representations consisting of a single fundamental fermionic form for all characters of the logarithmic conformal field theory models with central charge c(p,1), p>=2, and suggest a physical interpretation. We also show that it is possible to correctly extr... [more] We present fermionic quasi-particle sum representations consisting of a single fundamental fermionic form for all characters of the logarithmic conformal field theory models with central charge c(p,1), p>=2, and suggest a physical interpretation. We also show that it is possible to correctly extract dilogarithm identities.

• Pure Gauge SU(2) Seiberg-Witten Theory and Modular Forms

  Kirsten Vogeler, Michael Flohr

  08/2006;

  We identify the spectral curve of pure gauge SU(2) Seiberg-Witten theory with the Weierstrass curve $\mathbbm{C}/L \ni z \mapsto (1,\wp(z),\wp(z)')$ and thereby obtain explicitely a modular form from which the moduli space parameter $u$ and lattice parameters $a$, $a_D$ can be derived in terms o... [more] We identify the spectral curve of pure gauge SU(2) Seiberg-Witten theory with the Weierstrass curve $\mathbbm{C}/L \ni z \mapsto (1,\wp(z),\wp(z)')$ and thereby obtain explicitely a modular form from which the moduli space parameter $u$ and lattice parameters $a$, $a_D$ can be derived in terms of modular respectively theta functions. We further discuss its relationship with the $c=-2$ triplet model conformal field theory.

• Virasoro representations and fusion for general augmented minimal models

  Holger Eberle, Michael Flohr

  04/2006;

  In this paper we present explicit results for the fusion of irreducible and higher rank representations in two logarithmically conformal models, the augmented c_{2,3} = 0 model as well as the augmented Yang-Lee model at c_{2,5} = -22/5. We analyse their spectrum of representations which is consisten... [more] In this paper we present explicit results for the fusion of irreducible and higher rank representations in two logarithmically conformal models, the augmented c_{2,3} = 0 model as well as the augmented Yang-Lee model at c_{2,5} = -22/5. We analyse their spectrum of representations which is consistent with the symmetry and associativity of the fusion algebra. We also describe the first few higher rank representations in detail. In particular, we present the first examples of consistent rank 3 indecomposable representations and describe their embedding structure. Knowing these two generic models we also conjecture the general representation content and fusion rules for general augmented c_{p,q} models. Comment: 42 pages, 17 pages appendix, 5 figures

• Indecomposable Representations in Z_n Symmetric b,c Ghost Systems via Deformations of the Virasoro Field

  Michael Flohr, Julia Voelskow

  03/2006;

  The Virasoro field associated to b,c ghost systems with arbitrary integer spin lambda on an n-sheeted branched covering of the Riemann sphere is deformed. This leads to reducible but indecomposable representations, if the new Virasoro field acts on the space of states, enlarged by taking the tensor ... [more] The Virasoro field associated to b,c ghost systems with arbitrary integer spin lambda on an n-sheeted branched covering of the Riemann sphere is deformed. This leads to reducible but indecomposable representations, if the new Virasoro field acts on the space of states, enlarged by taking the tensor product over the different sheets of the surface. For lambda=1, proven LCFT structures are made explicit through this deformation. In the other cases, the existence of Jordan cells is ruled out in favour of a novel kind of indecomposable representations.

• Notes on Generalised Nullvectors in logarithmic CFT

  Holger Eberle, Michael Flohr

  01/2006;

  In these notes we discuss the procedure how to calculate nullvectors in general indecomposable representations which are encountered in logarithmic conformal field theories. In particular, we do not make use of any of the restrictions which have been imposed in logarithmic nullvector calculations up... [more] In these notes we discuss the procedure how to calculate nullvectors in general indecomposable representations which are encountered in logarithmic conformal field theories. In particular, we do not make use of any of the restrictions which have been imposed in logarithmic nullvector calculations up to now, especially the quasi-primarity of all Jordan cell fields. For the quite well-studied c_{p,1} models we calculate examples of logarithmic nullvectors which have not been accessible to the older methods and recover the known representation structure. Furthermore, we calculate logarithmic nullvectors in the up to now almost unexplored general augmented c_{p,q} models and use these to find bounds on their possible representation structures.

• Notes on non-trivial and logarithmic CFTs with c=0

  Michael Flohr, Annekathrin Mueller-Lohmann

  10/2005;

  We examine the properties of two-dimensional conformal field theories (CFTs) with vanishing central charge based on the extended Kac-table for c_(9,6)=0 using a general ansatz for the stress energy tensor residing in a Jordan cell of rank two. Within this setup we will derive the OPEs and two point ... [more] We examine the properties of two-dimensional conformal field theories (CFTs) with vanishing central charge based on the extended Kac-table for c_(9,6)=0 using a general ansatz for the stress energy tensor residing in a Jordan cell of rank two. Within this setup we will derive the OPEs and two point functions of the stress energy tensor T(z) and its logarithmic partner field t(z) and illustrate this by a bosonic field realization. We will show why our approach may be more promising than those chosen in the literature so far, including a discussion on properties of the augmented minimal model with vanishing central charge such as full conformal invariance of the vacuum as a state in an irreducible representation, consequences on percolation from null vectors and the structure of representations within the Kac table. Furthermore we will present another solution to the c --> 0 catastrophe based on an logarithmic CFT tensor model. As example, we consider a tensor product of the well-known c=-2 logarithmic CFT with a four-fold Ising model. We give an overview of the possible configurations and various consequences on the two point functions and the OPEs of the stress energy tensor T(z) and its logarithmic partner field t(z). We will motivate that due to the full conformal invariance of the vacuum at c=0, we have to assume a Jordan cell for the identity since t(z) is now a descendant of a new h=0 field.

• Logarithmic torus amplitudes

  Michael Flohr, Matthias R. Gaberdiel

  10/2005;

  For the example of the logarithmic triplet theory at c=-2 the chiral vacuum torus amplitudes are analysed. It is found that the space of these torus amplitudes is spanned by the characters of the irreducible representations, as well as a function that can be associated to the logarithmic extension o... [more] For the example of the logarithmic triplet theory at c=-2 the chiral vacuum torus amplitudes are analysed. It is found that the space of these torus amplitudes is spanned by the characters of the irreducible representations, as well as a function that can be associated to the logarithmic extension of the vacuum representation. A few implications and generalisations of this result are discussed.

• Nonmeromorphic operator product expansion and C_2-cofiniteness for a family of W-algebras

  Nils Carqueville, Michael Flohr

  09/2005;

  We prove the existence and associativity of the nonmeromorphic operator product expansion for an infinite family of vertex operator algebras, the triplet W-algebras, using results from P(z)-tensor product theory. While doing this, we also show that all these vertex operator algebras are C_2-cofinite... [more] We prove the existence and associativity of the nonmeromorphic operator product expansion for an infinite family of vertex operator algebras, the triplet W-algebras, using results from P(z)-tensor product theory. While doing this, we also show that all these vertex operator algebras are C_2-cofinite.

• Proposal for a CFT interpretation of Watts' differential equation for percolation

  Michael A. I. Flohr, Annekathrin Mueller-Lohmann

  07/2005;

  G. M. T. Watts derived that in two dimensional critical percolation the crossing probability Pi_hv satisfies a fifth order differential equation which includes another one of third order whose independent solutions describe the physically relevant quantities 1, Pi_h, Pi_hv. We will show that this di... [more] G. M. T. Watts derived that in two dimensional critical percolation the crossing probability Pi_hv satisfies a fifth order differential equation which includes another one of third order whose independent solutions describe the physically relevant quantities 1, Pi_h, Pi_hv. We will show that this differential equation can be derived from a level three null vector condition of a rational c=-24 CFT and motivate how this solution may be fitted into known properties of percolation.

• Four-Point Functions in Logarithmic Conformal Field Theories

  Michael Flohr, Marco Krohn

  04/2005;

  The generic structure of 4-point functions of fields residing in indecomposable representations of arbitrary rank is given. The used algorithm is described and we present all results for Jordan-rank $r=2$ and $r=3$ where we make use of permutation symmetry and use a graphical representation for the ... [more] The generic structure of 4-point functions of fields residing in indecomposable representations of arbitrary rank is given. The used algorithm is described and we present all results for Jordan-rank $r=2$ and $r=3$ where we make use of permutation symmetry and use a graphical representation for the results. A number of remaining degrees of freedom which can show up in the correlator are discussed in detail. Finally we present the results for two-logarithmic fields for arbitrary Jordan-rank. Comment: latex 33 pages, 1 figure

• A Note on Four-Point Functions in Logarithmic Conformal Field Theory

  Michael Flohr, Marco Krohn

  02/2005;

  The generic structure of 4-point functions of fields residing in indecomposable representations of arbitrary rank is given. The presented algorithm is illustrated with some non-trivial examples and permutation symmetries are exploited to reduce the number of free structure-functions, which cannot be... [more] The generic structure of 4-point functions of fields residing in indecomposable representations of arbitrary rank is given. The presented algorithm is illustrated with some non-trivial examples and permutation symmetries are exploited to reduce the number of free structure-functions, which cannot be fixed by global conformal invariance alone.

• Explicit Formulas for the Scalar Modes in Seiberg-Witten Theory with an Application to the Argyres-Douglas Point

  Nikolas Akerblom, Michael Flohr

  10/2004;

  General formulas for the scalar modes a_i and a^i_D in the Seiberg-Witten SU(N) setting are derived in the cases with and without massive hypermultiplets. Subsequently these formulas are applied in a study of the SU(3) Argyres-Douglas point. We use this example to study the question, whether the sca... [more] General formulas for the scalar modes a_i and a^i_D in the Seiberg-Witten SU(N) setting are derived in the cases with and without massive hypermultiplets. Subsequently these formulas are applied in a study of the SU(3) Argyres-Douglas point. We use this example to study the question, whether the scalar modes admit an interpretation in terms of BPS mass states everywhere in moduli space. The paper collects, in an appendix, various facts on the function Lauricella F_D^(n), which naturally appears in the derived formulas.

• Logarithmic Conformal Field Theory - or - How to Compute a Torus Amplitude on the Sphere

  Michael A. I. Flohr

  07/2004;

  We review some aspects of logarithmic conformal field theories which might shed some light on the geometrical meaning of logarithmic operators. We consider an approach, put forward by V. Knizhnik, where computation of correlation functions on higher genus Riemann surfaces can be replaced by computat... [more] We review some aspects of logarithmic conformal field theories which might shed some light on the geometrical meaning of logarithmic operators. We consider an approach, put forward by V. Knizhnik, where computation of correlation functions on higher genus Riemann surfaces can be replaced by computations on the sphere under certain circumstances. We show that this proposal naturally leads to logarithmic conformal field theories, when the additional vertex operator insertions, which simulate the branch points of a ramified covering of the sphere, are viewed as dynamical objects in the theory. We study the Seiberg-Witten solution of supersymmetric low energy effective field theory as an example where physically interesting quantities, the periods of a meromorphic one-form, can effectively be computed within this conformal field theory setting. We comment on the relation between correlation functions computed on the plane, but with insertions of twist fields, and torus vacuum amplitudes. Comment: LaTeX, 38 pp. 3 figures (provided as eps and as pdf). Contribution to the Ian Kogan Memorial Volume "From Fields to Strings: Circumnavigating Theoretical Physics"