Past seminars

Academic year: September 2002 - September 2003

I study a chiral N=1, U(N) field theory in the context of the Dijkgraaf-Vafa correspondence. The model contains one adjoint, one conjugate symmetric and one antisymmetric chiral multiplet, as well as eight fundamentals. I discuss the generalized Konishi anomalies and compare the chiral ring relations they induce with the loop equations of the matrix model defined by the tree-level superpotential of the field theory. Surprisingly, the matrix model is well-defined only if the number of flavors equals two! Despite this mismatch, the 1/N expansion of the loop equations agrees with the generalized Konishi constraints. This indicates that the matrix model - gauge theory correspondence should generally be modified when applied to theories with net chirality.

Place:  ULB, Campus Plaine, 2.NO.6.10
Time:   Thursday, September 11, 2003 at 10:30

 

I will discuss the process of relaxation back to thermal equilibrium for two systems: a CFT in finite volume and a black hole. Relaxation of black hole is described by the quasi-normal modes. For a (1+1)-dimensional CFT the analysis shows two different types of relaxation: exponential decay for high temperature and oscillatory behavior for zero temperature. I will illustrate the intermediate regime for free fields. For a strongly-coupled CFT dual to supergravity on AdS3 the transition between two regimes is the well-known Hawking-Page transition. I will speculate on possible relation to the problem of the information loss and its resolution within the AdS/CFT correspondence.

Place:  ITF, KU Leuven, Celestijnenlaan D06.34
Time:   Wednesday, June 18, 2003 at 13:30

 

This talk is about recent developments concerning time-dependent compactifications of string/M-theory. Such compactifications may avoid a no-go theorem which, in the time-independent case, forbids accelerating four-dimensional cosmologies.

Place:  ITF, KU Leuven, Celestijnenlaan D06.34
Time:   Wednesday, June 18, 2003 at 10:30

 

Place:  ULB, Campus Plaine, Forum A
Time:   Wednesday, June 11, 2003 at 13:30

 

Place:  ULB, Campus plaine, Forum A
Time:   Wednesday, June 11, 2003 at 10:30

 

Del Pezzo surfaces and toroidal compactifications of M-theory share several algebraic structures. In particular the lattice of divisors (2-cycles) of positive genus and positive degree is the root lattice of some Borcherds superalgebra which extends the usual U-duality algebra. Moreover this superalgebra can be used to recover the bosonic field content of the theory, with the equations of motion. The moduli of the theory appears as the second cohomology group of the del Pezzo surface. This approach is useful to deal with triangles of supergravities and can be used to prove the symmetry of the "Magic Triangle" of coset theories, and to construct new (symmetric) triangles.

Place:  ULB, Campus plaine, Forum G
Time:   Wednesday, June 04, 2003 at 13:30

 

Place:  ULB, Campus plaine, Forum G
Time:   Wednesday, June 04, 2003 at 10:30

 

See the website of the Belgian Physical Society.

Place:  University of Ghent
Time:   Tuesday, May 27, 2003 and Wednesday, May 28, 2003

 

Abstract (postscript file).

Place:  ITF, KU Leuven, Celestijnenlaan: 200D.06.34
Time:   Tuesday, May 20, 2003 at 10:30

Place:  200D.06.32  
Time:   Tuesday, May 20, 2003 at 13:30
           
Place:  200S.00.03  
Time:   Wednesday, May 21, 2003 at 10:30

Place:  200S.00.03  
Time:  Wednesday, May 21, 2003 at 13:30

Place:  200D.05.11  
Time:   Friday, May 23, 2003 at 10:30

Place:  200D.06.32  
Time:   Friday, May 23, 2003 at 13:30
           
Place:  200D.06.34  
Time:   Monday, May 26, 2003 at 10:30

Place: 200D.06.34  
Time:   Monday, May 26, 2003 at 13:30

 

Place:  ULB, Campus plaine, Forum G
Time:   Wednesday, May 14, 2003 at 13:30

 

The decay of unstable closed/open string backgrounds is an important process which has been studied extensively over the last years. Since the exact construction of such time dependent solutions of string theory is not yet understood, most of our present insights rely on the conjectured relation with renormalization group flows in the 2D world-sheet theory. We will discuss the existing evidence for such a relation, review some of the known results about RG flows in 2D field theories and conclude with a few remarks on the issues and ideas that are currently explored concerning the construction of exact solutions.

Place:  ULB, Campus plaine, Forum G
Time:   Wednesday, May 07, 2003 at 13:30

 

I will explicitly derive various classical solutions of M-theory and show how they are inter-related by strings of dualities. Some dualities involve theories living in different dimensions. I will discuss various limits of solutions and briefly show how they relate to ideas such as holography and braneworlds.

These talks will be at a very basic level and calculationally explicit-- a working knowledge of general relativity will be sufficient.

Place:  ULB, Campus plaine, Forum C (part I+II)
Time:   Wednesday, May 07, 2003 at 10:30 and Wednesday, May 14, 2003 at 10:30

 

We describe a systematic method of studying the action of the T-duality group O(d,d) on space-time fermions and R-R field strengths and potentials in type-II string theories, based on space-time supersymmetry.

This talk is part of the PhD students journal club. These talks will be held at a basic level and in an informal manner. They are mainly directed at an audience with little prior knowledge of the subject. Asking questions is encouraged.

Place:  KU Leuven, Celestijnenlaan 200D.06.32
Time:   Wednesday, April 30, 2003 at 13:30

 

We review the recent work of Connes and Kreimer on the Hopf algebra structure of the process of renormalization in Quantum Field Theory. We then introduce normal coordinates on the infinite dimensional group $G$ introduced by Connes and Kreimer in their analysis of the Hopf algebra of rooted trees. We study the primitive elements of the algebra and show that they are generated by a simple application of the inverse Poincar\'e lemma, given a closed left invariant 1-form on $G$. For the special case of the ladder primitives, we find a second description that relates them to the Hopf algebra of functionals on power series with the usual product. Either approach shows that the ladder primitives are given by the Schur polynomials. The relevance of the lower central series of the dual Lie algebra in the process of renormalization is also discussed, leading to a natural concept of $k$-primitiveness, which classifies (sums of products of) Feynman diagrams according to the complexity of their renormalization. Interrelations with Butcher's work on Runge-Kutta methods and Sorkin's proposal for a generalized Quantum Mechanics are also pointed out.

Place:  KU Leuven, Celestijnenlaan 200C.01.D
Time:   Wednesday, April 30, 2003 at 10:30

 

Place:  Catholic University of Louvain (UCL)
            2, Chemin du Cyclotron, Tower E, 3rd floor, e-364
            1348 Louvain-la-Neuve
            Building Marc de Hemptinne
            Seminar Room of the Institute of Nuclear Physics
Time:   Tuesday, April 22, 2003, 15:00-17:00
            Wednesday, April 23, 2003, 10:00-12:00
            Wednesday, April 23, 2003, 14:30-16:00
            Thursday, April 24, 2003, 10:00-12:00
            Thursday, April 24, 2003, 14:30-16:00
            Friday, April 25, 2003, 10:00-12:00

 

Francqui lecture

Place:  VUB, Pleinlaan, room G022
Time:   Wednesday, April 16, 2003 at 13:30

 

Francqui lecture

Place:  VUB, Pleinlaan, room G022
Time:   Wednesday, April 16, 2003 at 10:30

 

Followed by a board meeting and reception

Place:  Campus UIA, Wilrijk, Antwerpen, Auditorium S1
Time:   Monday, April 14, 2003, 10:00-17:00

 

String/M theory has an infinite number of vacua of which a very large number resembles the Standard Model of elementary particle physics. This raises the important question whether string/M theory leads to any testible predictions. In a recent paper Michael Douglas has proposed a `statistical description' of string/M theory vacua which should (in principle) be able to answer this question. Moreover, this description should (also in principle) tell us where to look for the standard model in the moduli space of string/M theory vacua.

In this informal seminar I will explain the main points of this paper by M. Douglas: hep-th/0303194.

Place:  ITF, KU Leuven, Celestijnenlaan 200D, 06.34
Time:   Wednesday, April 09, 2003 at 13:30

 

We study semiclassical states or coherent states for the classical Schwarzschild black hole in the framework of canonical quantisation of general relativity. Information about the horizon is naturally encoded in these states, which manifests itself as a special region of space-time.

Place:  ITF, KU Leuven, Celestijnenlaan 200D, 06.34
Time:   Wednesday, April 09, 2003 at 10:30

 


Place:  ITF, KU Leuven, Celestijnenlaan 200D, 06.32
Time:   Monday, April 07, 2003 at 13:30

 

Based on work with J. Kalkkinen, see hep-th/0212081 and hep-th/0302164.

Place:  ULB, Campus plaine, Forum G
Time:   Wednesday, April 02, 2003 at 13:45

 

After a brief introduction on superstring formalism developed by N. Berkovits, we discuss the removal of pure spinor constraints, the construction of vertex operators and the superconformal algebra for superstrings in 10 dimensions. We present some applications of our formalism to superparticles, to non-commutative superspace, and to string theory on generic backgrounds.

Place:  ULB, Campus plaine, building NO, fifth floor, Salle Solvay
Time:   Wednesday, April 02, 2003 at 12:30

 

Place:  ULB, Campus Plaine, Forum F
Time:   Wednesday, April 02, 2003 at 10:30

 

The low-energy effective action of type-I superstring theory in ten dimensions is obtained performing a truncation of type-IIB supergravity in a background where D9-branes are present. The open sector corresponds to the first order in the low-energy expansion of the D9-brane action in a type-I background. There are two ways of performing a type-I truncation of the D9-brane action, and we argue that they are in correspondence with the open sector of the low-energy effective action of the two different consistent ten-dimensional type-I string theories, namely the SO(32) superstring and the USp(32) non-supersymmetric string.

Place:  ITF, KULeuven, Celestijnenlaan 200C, C01.A
Time:   Wednesday, March 26, 2003 at 13:30

 

We consider what happens to an M2-brane probe when Minkowski space is dimensionally reduced to a fluxbrane solution of IIA supergravity. Given that fluxbrane reductions generally break supersymmetry, we look at how supersymmetry is realised on the D2-brane probe after dualisation. We also show how to extend this to more general non-linear sigma models.

Place:  ITF, KULeuven, Celestijnenlaan 200S, S00.03
Time:   Wednesday, March 26, 2003 at 10:30

 

Review of recent results in Open String Field Theory, especially in regard to tachyon condensation and Vacuum String Field Theory. New (and old) problems. A new challenge: Open String Field Theory and integrability.

Place:  ULB, campus Plaine, forum A
Time:   Wednesday, March 19, 2003 at 13:30

 

Francqui lecture

Place:  VUB, Pleinlaan, room G022
Time:   Wednesday, March 19, 2003 at 10:30

 

based on hep-th/0210291 and hep-th/0211249

Place:  ULB, Campus Plaine, forum A
Time:   Wednesday, March 12, 2003 at 13:30

Francqui lecture

Place:  VUB, Pleinlaan, room G022
Time:   Wednesday, March 12, 2003 at 10:30

 

We give an introduction to extremal black holes, and how they can be found as solutions in supergravity theories. We consider mainly the N=2,D=4 case and review some aspects of electromagnetic duality, black hole entropy, and the near-horizon geometry. References: hep-th/9812160 and hep-th/0203076.

This talk is part of the PhD students journal club. These talks will be held at a basic level and in an informal manner. They are mainly directed at an audience with little prior knowledge of the subject. Asking questions is encouraged.

Place:  ULB, Campus Plaine, forum G
Time:   Wednesday, March 05, 2003 at 13:30

 

Francqui lecture

Place:  VUB, Pleinlaan, room G022
Time:   Wednesday, March 05, 2003 at 10:30

 

Inaugural lecture of the national Francqui chair

Powerpoint presentation: FrancquiChair.ppt

Place:  VUB, Pleinlaan, Auditorium G023
Time:   Wednesday, February 26, 2003 at 14:00

 

We still lack a consistent quantum description of how the fundamental geometric degrees of freedom of space-time interact among themselves and with other matter excitations at the very smallest length scales. Such a theory of quantum gravity would provide a micro-description of space-time geometry and explain at the same time why at large distances the universe is well described by classical general relativity. In my talk I will review some of the results and lessons learned from "Lorentzian dynamical triangulations". This is a recent attempt to construct a non-perturbative theory of quantum gravity by "summing over all geometries". From the outset, its formulation does not distinguish any particular metric background structure, and "quantum space-time" emerges only as a solution of the quantum dynamics of geometry.

Place:  ULB, Campus Plaine, forum G
Time:   Wednesday, February 19, 2003 at 13:30

 

We give an introduction to N=2 gauged supergravities in D=4 and D=5. We first review the elements necessary to define the ungauged action (e.g susy multiplets, duality transformations, special geometry,...) and then go on to describe the gauging procedure. References: hep-th/9605032 and hep-th/0102114

This talk is part of the PhD students journal club. These talks will be held at a basic level and in an informal manner. They are mainly directed at an audience with little prior knowledge of the subject. Asking questions is encouraged.

Part I:
Place:   ITF, KULeuven, Celestijnenlaan 200G, D05.34
Time:     Wednesday, February 12, 2003 at 13:30

Part II:
Place:   ULB, Campus Plaine, forum B
Time:    Wednesday, February 19, 2003 at 10:30

Part III:
Place:  ULB, Campus Plaine, building NO, fifth floor, Salle Solvay
Time:    Wednesday, February 26, 2003 at 10:30

 

We first review the notion of exact background and give some examples for the bosonic string. We then review the hybrid formalism(s) for the GS string and finally we show how to use them to describe type II superstrings exact superconformal σ-models on pp-wave backgrounds with constant and non-constant RR curvature forms.

Place:  ITF, KU Leuven, Celestijnenlaan 200D, 06.34
Time:   Wednesday, February 05, 2003 at 13:30

 

We give a brief introduction to modules and (the mathematical aspects of) K-theory. Then we proceed to analyse the classification of RR-charges and RR-fields using K-theory. We will argue that in order to make this classification we need an inifinite set of D-branes reduced to a finite set by tachyon condensation. This talk is largely based on hep-th/0007175 and references therein.

This talk is part of the PhD students journal club. The talks will be held at a basic level and in an informal manner. They are mainly directed at an audience with little prior knowledge of the subject. Asking questions is encouraged.

Place:  ITF, KU Leuven, Celestijnenlaan 200, D06.34 (part I, 05/02/2003), G01.73 (part II, 12/02/2003)
Time:   Wednesday, February 05, 2003 at 10:30 and February 12, 2003 at 10:30

 

Place:  ULB, Campus Plaine, building NO, fifth floor, Salle Solvay
Time:   Thursday, December 19, 2002 at 13:30

 

We review how the dynamics of the Einstein-dilaton-p-form system in the vicinity of a spacelike singularity can be asymptotically described, at each spatial point, as a billiard motion in a region of Lobachevsky n-space. For 11-dimensional and 10-dimensional supergravities, this region can be identified with the fundamental Weyl chamber of a Kač-Moody algebra of hyperbolic type. We comment on the possible implications of this result.

Place:  ULB, Campus Plaine, forum G
Time:   Thursday, December 19, 2002 at 10:30

 

We review the symmetries found in supergravity theories. We will then show that the maximal supergravity theories, including their gravitational sectors, in ten and eleven dimensions can be described by a non-linear realisation. Assuming that the underlying symmetry is a Kač-Moody algebra we show that this must contain $E_{11}$. We conjecture that $E_{11}$ is a symmetry of the maximal supergravity theories and present evidence for it. In particular we show that the conjecture requires a dual description of gravity based on the fields $h^a{}_b$ and $h_{a_1\ldots a_8,b}$. We give such a formulation of gravity.

Place:  ULB, Campus Plaine, building NO, fifth floor, Salle Solvay
Time:   Thursday, December 12, 2002 at 13:30

 

All ten-dimensional fermionic strings, supersymmetric or not, live in subspaces of the Hilbert space of the 26-dimensional bosonic string compactified on E8 X SO(16) lattices. Using the global properties of this group, purely bosonic considerations yield a classification of all fermionic D-branes - including their charge conjugation and chirality assignments - and the value of their tensions. They also yield the orientifold tensions and all the Chan-Paton groups which render open fermionic strings tadpole and anomaly-free, including the SO(32) Chan-Paton group of Type I. These features of the bosonic string suggest a search for a possible non perturbative dynamical mechanism which would decouple the fermionic subspaces from the remaining states. The existence of such a mechanism would considerably enlarge the scope of the M-theory quest. Reference : Auttakit Chattaraputi, François Englert, Laurent Houart and Anne Taormina, The bosonic mother of fermionic D-branes, JHEP 0209(2002) 037 (arXiv:hep-th/0207238), and references therein.

Place:  ULB, Campus Plaine, forum G
Time:   Thursday, December 12, 2002 at 10:30

 

The recent Nobel price attributed to Raymond Davis Jr. and Masatoshi Koshiba "for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos" is used as an argument to review the experimental situation on neutrinos masses and oscillation, with special enphasis on the oscillation evidence provided by the solar neutrinos experiments.

Place:  ITF, KU Leuven, Celestijnenlaan 200D, 05.11
Time:   Thursday, December 05, 2002 at 13:30

 

Several key issues in the NSR formulation of superstrings will be introduced. Subsequently, we will focus on the (im)possibility of non-trivial RR backgrounds. This talk will essentially start from scratch.

Place:  ITF, KU Leuven, Celestijnenlaan 200D, 06.34
Time:   Thursday, December 05, 2002 at 10:30

 

By studying the coset F_4/SO(9) one finds interesting relations between higher spin representations of SO(9), the little group of massless states in 11 dimensions, which extends the supersymmetry between the 11-dimensional supergravity multiplet to an infinite set of higher spin triplets. I will discuss how these representations are solutions to a Dirac-like equation due to Kostant. I will also discuss continuous spin representations in 11 dimensions which also contains an infinite set of higher spin multiplets.

Place:  ULB, Campus Plaine, building NO, fifth floor, Salle Solvay
Time:   Thursday, November 28, 2002 at 13:30

 

For semisimple groups, possibly multiplied by U(1)'s, the number of Yang-Mills gauge fields is equal to the number of generators of the group. In this paper, it is shown that, for non-semisimple groups, the number of Yang-Mills fields can be larger. These additional Yang-Mills fields are not irrelevant because they appear in the gauge transformations of the original Yang-Mills fields. Such non-semisimple Yang-Mills theories may lead to physical consequences worth studying. The non-semisimple group with only two generators that do not commute is studied in detail. [hep-th/0210214 ]

Place:  ULB, Campus Plaine, forum G
Time:   Thursday, November 28, 2002 at 10:30

 

Motivated by recent works of Sen and Gibbons, we study the evolution of a flat and homogeneous universe dominated by tachyon matter. In particular, we analyse the necessary conditions for inflation in the early roll of a single tachyon field. [hep-th/0204070 ]

Place:  ITF, KU Leuven, Celestijnenlaan 200D, 05.11
Time:   Thursday, November 14, 2002 at 13:30

 

According to Belinsky, Khalatnikov and Lifshitz, gravity near a space-like singularity reduces to a set of decoupled one-dimensional mechanical models at each point in space. We point out that these models fall into a class of conformal mechanical models first introduced by de Alfaro, Fubini and Furlan (DFF). The deformation used by DFF to render the spectrum discrete corresponds to a negative cosmological constant. The wave function of the universe is the zero-energy eigenmode of the Hamiltonian, also known as the spherical vector of the representation of the conformal group SO(1,2). A new class of conformal quantum mechanical models is constructed, based on the quantization of nilpotent coadjoint orbits, where the conformal group is enhanced to an ADE non-compact group for which the spherical vector is known. [hep-th/0209044 ]

Place:  ITF, KU Leuven, Celestijnenlaan 200S, 01.05
Time:   Thursday, November 14, 2002 at 10:30

 

Place:  VUB, Campus Pleinlaan, building B, room B0.31 (morning), building E, room E0.6 (afternoon)
Time:   Friday, November 08, 2002

 

Arguments from string theory show that for a large class of N=1 supersymmetric gauge theories the effective superpotential is exactly given by a summation of planar diagrams of the same gauge theory. This perturbative computation reduces to a matrix model whose action is the tree-level superpotential. These results are obtained without assuming any conjectured dualities and can be used as a systematic method to compute instanton effects perturbatively. This method allows us to see many non-perturbative effects, such as the Seiberg-Witten solutions of N=2 theories and the consequences of Montonen-Olive S-duality in N=4 from a completely perturbative planar point of view.

Place:  ULB, Campus Plaine, forum G (morning); building NO, fifth floor, Salle Solvay (afternoon)
Time:   Thursday, October 31, 2002 at 10:30 and 13:30

 

We give an introduction to Scherk-Schwarz dimensional reduction and apply this procedure to reduce IIB supergravity to nine dimensional massive supergravity.

Place:  ITF, KU Leuven, Celestijnenlaan 200D, 05.11
Time:   Thursday, October 24, 2002 at 13:30

 

Following an article by Corrigan et al. we generalize the instanton solution of Yang-Mills to more than four dimensions. Next, we try to construct a higher order perturbation of Yang-Mills that still admits these kind of solutions. This turns out to be very restrictive. In the abelian case we find the Born-Infeld action and in the non-abelian case we use this procedure to construct the D-brane effective action.

Place:  ITF, KU Leuven, Celestijnenlaan 200D, 06.34
Time:   Thursday, October 24, 2002 at 10:30

 

This talk will review several aspects of the dynamical relaxation of the cosmological constant through membrane nucleation.

Place:  ULB, Campus Plaine, building NO, fifth floor, Salle Solvay
Time:   Thursday, October 17, 2002 at 13:30

 

Cosmological observations suggest that a realistic theory of gravity should allow the possibility of vacua with a positive cosmological constant. These are not easy to find in supergravity theories. We (in collaboration with Pietro Fre and Mario Trigiante) show how to obtain such solutions in the context of N=2 supergravity. [hep-th/0205119]

Place:  VUB, Campus Pleinlaan, building G, 1G.003
Time:   Thursday, October 17, 2002 at 10:30

 

This talk will review the construction of a new Penrose limit of AdS5 x S5 and its applications. The relevant reference is hep-th/0209201.

Place:  ULB, Campus Plaine, building NO, fifth floor, salle Solvay
Time:   Thursday, October 10, 2002 at 13:30

 

We construct matter couplings of five-dimensional SUGRA with the help of conformal tensor calculus. Firstly, we determine the Weyl multiplet. In the background of this multiplet other representations of superconformal algebra (vector- and hyper- multiplets) can be defined. The next step is the construction of superconformal invariant actions for these multiplets. Finally, we present some black hole solutions of five-dimensional SUGRA coupled to an arbitrary number of vector multiplets.
References: hep-th/0104113, hep-th/0205230.

Place:  VUB, Campus Pleinlaan, building G, 1G.003
Time:   Thursday, October 10, 2002 at 10:30

 

A spinning D3-brane undergoes a phase transition to a naked singularity which, from the braneworld point of view, corresponds to the apparent graviton speed passing from subluminal to superluminal. We investigate this phase transition from the dual perspectives of braneworld scenarios and holography. We discuss the relevance of the thermodynamic stability domains of a spinning D3-brane to the physics of braneworld scenarios. We also describe various gravitational Lorentz violations which arise from static D3-branes.

Place:  ITF, 6th floor, Celestijnenlaan 200D, Leuven
Time:   Thursday, October 03, 2002 at 13:30

 

Using a mathematical framework which provides a generalization of the de Rham complex (well-designed for p-form gauge fields), we study the gauge structure and duality properties of theories for free gauge fields transforming in arbitrary irreducible representations of GL(D,R). We prove a generalization of the Poincaré lemma which enables us to solve the above-mentioned problems in a systematic and unified way.

Place:  ITF, 6th floor, Celestijnenlaan 200D, Leuven
Time:   Thursday, October 03, 2002 at 10:30

 

We consider four-dimensional superconformal field theories coupled to three-dimensional superconformal boundary or defect degrees of freedom. We present a superspace formulation for a model preserving N=4, d=3 supersymmetry and the conformal symmetries under which the boundary/defect is invariant. This model has been studied as a generalization of the AdS/CFT correspondence and is conjectured to be dual to a D3/D5 brane system whose near-horizon limit is AdS_5*S5 with a D5 brane wrapping an AdS_4*S2 submanifold. We show that the beta functions of this model vanish to all orders in perturbation theory, such that the models remain superconformal upon quantization. Moreover we present a similar analysis for a four-dimensional theory with a two-dimensional defect corresponding to a D3/D3 brane system with a D3 brane wrapping an AdS_3*S1 submanifold. Here there are additional interesting features present due to the two-dimensional nature of the defect.

Place:  Campus Plaine, building NO, room N06.10
Time:   Thursday, September 26, 2002 at 14:30

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