SwePub - sökning: WFRF:(Gran Ulf 1973)

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1.	Adawi, Tom, 1970, et al. (författare) Superembeddings, nonlinear supersymmetry and five-branes 1997 Ingår i: Int.J.Mod.Phys.A13:4691-4716,1998. Tidskriftsartikel (refereegranskat)abstract We examine general properties of superembeddings, i.e., embeddings of supermanifolds into supermanifolds. The connection between an embedding procedure and the method of non-linearly realised supersymmetry is clarified, and we demonstrate how the latter arises as a special case of the former. As an illustration, the super-5-brane in 7 dimensions, containing a self-dual 3-form world-volume field strength, is formulated in both languages, and provides an example of a model where the embedding condition does not suffice to put the theory on-shell.
2.	Cederwall, Martin, 1961, et al. (författare) Finite tensor deformations of supergravity solitons 1998 Ingår i: J. High Energy Phys. 9902:003,1999. Tidskriftsartikel (refereegranskat)abstract We consider brane solutions where the tensor degrees of freedom are excited. Explicit solutions to the full non-linear supergravity equations of motion are given for the M5 and D3 branes, corresponding to finite selfdual tensor or Born-Infeld field strengths. The solutions are BPS-saturated and half-supersymmetric. The resulting metric space-times are analysed.
3.	Adawi, Tom, 1970, et al. (författare) Goldstone tensor modes 1998 Ingår i: J. High Energy Phys. 9902:001,1999. Tidskriftsartikel (refereegranskat)abstract In the context of brane solutions of supergravity, we discuss a general method to introduce collective modes of any spin by exploiting a particular way of breaking symmetries. The method is applied to the D3, M2 and M5 branes and we derive explicit expressions for how the zero-modes enter the target space fields, verify normalisability in the transverse directions and derive the corresponding field equations on the brane. In particular, the method provides a clear understanding of scalar, spinor, and rank r tensorial Goldstone modes, chiral as well as non-chiral, and how they arise from the gravity, Rarita-Schwinger, and rank r+1 Kalb-Ramond tensor gauge fields, respectively. Some additional observations concerning the chiral tensor modes on the M5 brane are discussed.
4.	Baggioli, Matteo, et al. (författare) Collective modes of polarizable holographic media in magnetic fields 2021 Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2021:6 Tidskriftsartikel (refereegranskat)abstract We consider a neutral holographic plasma with dynamical electromagnetic interactions in a finite external magnetic field. The Coulomb interactions are introduced via mixed boundary conditions for the Maxwell gauge field. The collective modes at finite wave-vector are analyzed in detail and compared to the magneto-hydrodynamics results valid only at small magnetic fields. Surprisingly, at large magnetic field, we observe the appearance of two plasmon-like modes whose corresponding effective plasma frequency grows with the magnetic field and is not supported by any background charge density. Finally, we identify a mode collision which allows us to study the radius of convergence of the linearized hydrodynamics expansion as a function of the external magnetic field. We find that the radius of convergence in momentum space, related to the diffusive transverse electromagnetic mode, increases quadratically with the strength of the magnetic field.
5.	Baggioli, Matteo, et al. (författare) Holographic plasmon relaxation with and without broken translations 2019 Ingår i: Journal of High Energy Physics (JHEP). - : SPRINGER. - 1126-6708 .- 1029-8479. ; :9 Tidskriftsartikel (refereegranskat)abstract We study the dynamics and the relaxation of bulk plasmons in strongly coupled and quantum critical systems using the holographic framework. We analyze the dispersion relation of the plasmonic modes in detail for an illustrative class of holographic bottom-up models. Comparing to a simple hydrodynamic formula, we entangle the complicated interplay between the three least damped modes and shed light on the underlying physical processes. Such as the dependence of the plasma frequency and the effective relaxation time in terms of the electromagnetic coupling, the charge and the temperature of the system. Introducing momentum dissipation, we then identify its additional contribution to the damping. Finally, we consider the spontaneous symmetry breaking (SSB) of translational invariance. Upon dialing the strength of the SSB, we observe an increase of the longitudinal sound speed controlled by the elastic moduli and a decrease in the plasma frequency of the gapped plasmon. We comment on the condensed matter interpretation of this mechanism.
6.	Baggioli, Matteo, et al. (författare) Transverse collective modes in interacting holographic plasmas 2020 Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2020:4 Tidskriftsartikel (refereegranskat)abstract We study in detail the transverse collective modes of simple holographic models in presence of electromagnetic Coulomb interactions. We render the Maxwell gauge field dynamical via mixed boundary conditions, corresponding to a double trace deformation in the boundary field theory. We consider three different situations: (i) a holographic plasma with conserved momentum, (ii) a holographic (dirty) plasma with finite momentum relaxation and (iii) a holographic viscoelastic plasma with propagating transverse phonons. We observe two interesting new features induced by the Coulomb interactions: a mode repulsion between the shear mode and the photon mode at finite momentum relaxation, and a propagation-to-diffusion crossover of the transverse collective modes induced by the finite electromagnetic interactions. Finally, at large charge density, our results are in agreement with the transverse collective mode spectrum of a charged Fermi liquid for strong interaction between quasi-particles, but with an important difference: the gapped photon mode is damped even at zero momentum. This property, usually referred to as anomalous attenuation, is produced by the interaction with a quantum critical continuum of states and might be experimentally observable in strongly correlated materials close to quantum criticality, e.g. in strange metals.
7.	Beck, S., et al. (författare) All Killing superalgebras for warped AdS backgrounds 2018 Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2018:12 Tidskriftsartikel (refereegranskat)abstract We present all the symmetry superalgebras ? of all warped AdSk ×wMd − k, k > 2, flux backgrounds in d = 10, 11 dimensions preserving any number of supersymmetries. First we give the conditions for ? to decompose into a direct sum of the isometry algebra of AdSk and that of the internal space Md − k. Assuming this decomposition, we identify all symmetry superalgebras of AdS3 backgrounds by showing that the isometry groups of internal spaces act transitively on spheres. We demonstrate that in type II and d = 11 theories the AdS3 symmetry superalgebras may not be simple and also present all symmetry superalgebras of heterotic AdS3 backgrounds. Furthermore, we explicitly give the symmetry superalgebras of AdSk, k > 3, backgrounds and prove that they are all classical.
8.	Benjaminsson, Daniel, et al. (författare) Advanced study techniques for university students 2023 Ingår i: Proceedings Chalmers Conference on Teaching and Learning 2023. - 9789188041548 ; , s. 61-67 Konferensbidrag (refereegranskat)abstract The students starting at the Engineering Physics and Engineering Mathematics educations at Chalmers face challenges in terms of greatly increased workload and complexity of the subject matter compared to their previous education. Based on the experiences from teaching an introductory course in mechanics for nearly ten years (Ulf), the lack of efficient study techniques for a large number of students was identified. We have this year therefore offered the students a course in advanced study techniques (Daniel) tailored for university students, and also for their specific educations. We will here briefly describe the contents of the course and the preliminary impact on student learning.
9.	Berman, David S., et al. (författare) Deformation Independent Open Brane Metrics and Generalized Theta Parameters 2001 Ingår i: J. High Energy Phys.. ; 02, s. 012- Tidskriftsartikel (refereegranskat)
10.	Berman, David S., et al. (författare) Holographic Noncommutativity 2000 Ingår i: J. High Energy Phys. ; 05, s. 002- Tidskriftsartikel (refereegranskat)
11.	Cederwall, Martin, 1961, et al. (författare) D=3, N=8 conformal supergravity and the Dragon window 2011 Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2011:9 Tidskriftsartikel (refereegranskat)abstract We give a superspace description of D=3, N=8 supergravity. The formulation is off-shell in the sense that the equations of motion are not implied by the superspace constraints (but an action principle is not given). The multiplet structure is unconventional, which we connect to the existence of a "Dragon window", that is modules occurring in the supercurvature but not in the supertorsion. According to Dragon's theorem this cannot happen above three dimensions. We clarify the relevance of this window for going on the conformal shell, and discuss some aspects of coupling to conformal matter.
12.	Cederwall, Martin, 1961, et al. (författare) Generalised 11-Dimensional Supergravity 2000 Ingår i: proceedings of the Triangle Meeting ``Non-perturbative Methods in Field and String Theory'', NORDITA, Copenhagen, June 19-22, 2000, and the International Conference ``Quantization, Gauge Theory and Strings'' in memory of Efim Fradkin, Moscow, June 5-10, 2000.. Konferensbidrag (refereegranskat)
13.	Cederwall, Martin, 1961, et al. (författare) Manifestly Supersymmetric M-Theory 2000 Ingår i: J. High Energy Phys.. ; 10, s. 041- Tidskriftsartikel (refereegranskat)
14.	Cederwall, Martin, 1961, et al. (författare) (p,q) five-branes in nonzero B-field 1999 Ingår i: J. High Energy Phys. 0001:037,2000. Tidskriftsartikel (refereegranskat)abstract We consider type IIB (p,q) 5-branes in constant non-zero background tensor potentials, or equivalently, with finite constant field strength on the brane. At linear level, zero-modes are introduced and the physical degrees of freedom are found to be parametrised by a real 2- or 4-form field strength on the brane. An exact, SL(2;Z)-covariant solution to the full non-linear supergravity equations is then constructed. The resulting metric space-times are analysed, with special emphasis on the limiting cases with maximal values of the tensor. The analysis provides an answer to how the various background tensor fields are related to Born-Infeld degrees of freedom and to non-commutativity parameters.
15.	Cederwall, Martin, 1961, et al. (författare) Supersymmetric Corrections to Eleven-Dimensional Supergravity 2004 Ingår i: J. High Energy Phys. 0505 (2005) 052. Tidskriftsartikel (refereegranskat)abstract In this paper we study eleven-dimensional supergravity in its most general form. This is done by implementing manifest supersymmetry (and Lorentz invariance) through the use of the geometric (torsion and curvature) superspace Bianchi identities. These identities are solved to linear order in a deformation parameter introduced via the dimension zero supertorsion given in its most general form. The theory so obtained is referred to as the deformed theory (to avoid the previously used term "off-shell"). An important by-product of this result is that any higher derivative correction to ordinary supergravity of the same dimension as R^4, but not necessarily containing it, derived e.g. from M-theory, must appear in a form compatible with the equations obtained here. Unfortunately we have not yet much to say about the explicit structure of these corrections in terms of the fields in the massless supermultiplet. Our results are potentially powerful since if the dimension zero torsion could be derived by other means, our reformulation of the Bianchi identities as a number of algebraic relations implies that the full theory would be known to first order in the deformation, including the dynamics. We mention briefly some methods to derive the information needed to obtain explicit answers both in the context of supergravity and ten-dimensional super-Yang-Mills where the situation is better understood. Other relevant aspects like spinorial cohomology, the role of the 3- and 6-form potentials and the connection of these results to M2 and M5 branes are also commented upon.
16.	Gran, Ulf, 1973, et al. (författare) AdS backgrounds from black hole horizons 2013 Ingår i: Classical and Quantum Gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 30:5, s. Art. no. 055014- Tidskriftsartikel (refereegranskat)abstract We utilize the classification of IIB horizons with 5-form flux to present a unified description for the geometry of AdS(n), n = 3, 5, 7 solutions. In particular, we show that all such backgrounds can be constructed from eight-dimensional 2-strong Calabi-Yau geometries with torsion which admit some additional isometries. We explore the geometry of AdS(3) and AdS(5) solutions but we do not find AdS(7) solutions.
17.	Gran, Ulf, 1973, et al. (författare) All superalgebras for warped AdS2 and black hole near horizon geometries 2019 Ingår i: Classical and Quantum Gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 36:23 Tidskriftsartikel (refereegranskat)abstract We identify all symmetry superalgebras ? of near horizon geometries of black holes with a Killing horizon, assuming the solution is smooth and that the spatial cross section of the event horizon is compact without boundary. This includes all warped AdS2 backgrounds with the most general allowed fluxes in 10- and 11-dimensional supergravities. If the index of a particular Dirac operator vanishes, we find that the even symmetry subalgebra decomposes as ?0=??(2,ℝ)⊕?0, where ?0/? is the Lie algebra of a group that acts transitively and effectively on spheres, and ? is the center of ?. If the Dirac operator index does not vanish, then the symmetry superalgebra is nilpotent with one even generator. We also demonstrate that there are no near horizon geometries, and also therefore no warped AdS2 backgrounds, in 10- and 11-dimensions that preserve more than 16 supersymmetries.
18.	Gran, Ulf, 1973 (författare) Branestorming : on various aspects of ρ-branes 1999 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)
19.	Gran, Ulf, 1973, et al. (författare) Classification, geometry and applications of supersymmetric backgrounds 2019 Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573. ; 11:5, s. 1-87 Forskningsöversikt (refereegranskat)abstract We review the remarkable progress that has been made the last 15 years towards the classification of supersymmetric solutions with emphasis on the description of the bilinears and spinorial geometry methods. We describe in detail the geometry of backgrounds of key supergravity theories, which have applications in the context of black holes, string theory, M-theory and the AdS/CFT correspondence unveiling a plethora of existence and uniqueness theorems. Some other aspects of supersymmetric solutions like the Killing superalgebras and the homogeneity theorem are also presented, and the non-existence theorem for certain smooth supergravity flux compactifications is outlined. Amongst the applications described is the proof of the emergence of conformal symmetry near black hole horizons and the classification of warped AdS backgrounds that preserve more than 16 supersymmetries.
20.	Gran, Ulf, 1973, et al. (författare) Classification of IIB backgrounds with 28 supersymmetries 2009 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract We show that all IIB backgrounds with strictly 28 supersymmetries are locally isometric to the plane wave solution of arXiv:hep-th/0206195. Moreover, we demonstrate that all solutions with more than 26 supersymmetries and only 5-form flux are maximally supersymmetric. The N=28 plane wave solution is a superposition of the maximally supersymmetric IIB plane wave with a heterotic string solution. We investigate the propagation of strings in this background, find the spectrum and give the string light-cone Hamiltonian.
21.	Gran, Ulf, 1973, et al. (författare) Classification of IIB backgrounds with 28 supersymmetries 2010 Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2010:1 Tidskriftsartikel (refereegranskat)abstract We show that all IIB backgrounds with strictly 28 supersymmetries are locally isometric to the plane wave solution of arXiv:hep-th/0206195. Moreover, we demonstrate that all solutions with more than 26 supersymmetries and only 5-form flux are maximally supersymmetric. The N=28 plane wave solution is a superposition of the maximally supersymmetric IIB plane wave with a heterotic string solution. We investigate the propagation of strings in this background, find the spectrum and give the string light-cone Hamiltonian.
22.	Gran, Ulf, 1973, et al. (författare) Dynamical symmetry enhancement near IIA horizons 2015 Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2015:6 Tidskriftsartikel (refereegranskat)abstract We show that smooth type IIA Killing horizons with compact spatial sections preserve an even number of supersymmetries, and that the symmetry algebra of horizons with non-trivial fluxes includes an sl$$ \mathfrak{s}\mathfrak{l} $$(2, ℝ) subalgebra. This confirms the conjecture of [1] for type IIA horizons. As an intermediate step in the proof, we also demonstrate new Lichnerowicz type theorems for spin bundle connections whose holonomy is contained in a general linear group.
23.	Gran, Ulf, 1973, et al. (författare) Dynamical symmetry enhancement near massive IIA horizons 2015 Ingår i: Classical and Quantum Gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 32:23, s. Art. Nr. 235004- Tidskriftsartikel (refereegranskat)abstract We prove that Killing horizons in massive IIA supergravity preserve an even number of supersymmetries, and that their symmetry algebra contains an ??(2,R) subalgebra, confirming the conjecture of [5]. We also prove a new class of Lichnerowicz type theorems for connections of the spin bundle whose holonomy is contained in a general linear group.
24.	Gran, Ulf, 1973, et al. (författare) Exotic holographic dispersion 2019 Ingår i: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; 2019:2 Tidskriftsartikel (refereegranskat)abstract For strongly interacting systems, where perturbation theory is not applicable, holographic duality is a powerful framework for computing e.g. dispersion relations. Using the standard Reissner-Nordström black hole as a holographic model for a (strange) metal, we obtain exotic dispersion relations for both plasmon modes and quasinormal modes for certain intermediate values of the charge of the black hole. The obtained dispersion relations show dissipative behavior which we compare to the generic expectations from the Caldeira-Leggett model for quantum dissipation. Based on these considerations, we investigate how holography can predict higher order corrections for strongly coupled physics.
25.	Gran, Ulf, 1973 (författare) GAMMA: A Mathematica package for performing gamma-matrix algebra and Fierz transformations in arbitrary dimensions 2001 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract We have developed a Mathematica package capable of performing gamma-matrix algebra in arbitrary (integer) dimensions. As an application we can compute Fierz transformations.
26.	Gran, Ulf, 1973, et al. (författare) Geometry of all supersymmetric four-dimensional N=1 supergravity backgrounds 2008 Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479 .- 1126-6708. ; 06:6, s. 102- Tidskriftsartikel (refereegranskat)abstract We solve the Killing spinor equations of ${\cal N}=1$ supergravity, with four supercharges, coupled to any number of vector and scalar multiplets in all cases. We find that backgrounds with N=1 supersymmetry admit a null, integrable, Killing vector field. There are two classes of N=2 backgrounds. The spacetime in the first class admits a parallel null vector field and so it is a pp-wave. The spacetime of the other class admits three Killing vector fields, and a vector field that commutes with the three Killing directions. These backgrounds are of cohomogeneity one with homogenous sections either $\bR^{2,1}$ or $AdS_3$ and have an interpretation as domain walls. The N=3 backgrounds are locally maximally supersymmetric. There are N=3 backgrounds which arise as discrete identifications of maximally supersymmetric ones. The maximally supersymmetric backgrounds are locally isometric to either $\bR^{3,1}$ or $AdS_4$.
27.	Gran, Ulf, 1973, et al. (författare) Geometry of all supersymmetric type I backgrounds 2007 Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479 .- 1126-6708. ; :8, s. 074- Tidskriftsartikel (refereegranskat)abstract We find the geometry of all supersymmetric type I backgrounds by solving the gravitino and dilatino Killing spinor equations, using the spinorial geometry technique, in all cases. The solutions of the gravitino Killing spinor equation are characterized by their isotropy group in Spin(9,1), while the solutions of the dilatino Killing spinor equation are characterized by their isotropy group in the subgroup Sigma(P) of Spin(9,1) which preserves the space of parallel spinors P. Given a solution of the gravitino Killing spinor equation with L parallel spinors, L = 1,2,3,4,5,6,8, the dilatino Killing spinor equation allows for solutions with N supersymmetries for any 0
28.	Gran, Ulf, 1973, et al. (författare) Getting at the learning in active learning 2015 Ingår i: Proceedings från 5:e Utvecklingskonferensen för Sveriges ingenjörsutbildningar. Konferensbidrag (refereegranskat)abstract We describe the efforts made to improve teaching and learning – and hence the pass-rate – in an introductory mechanics course, and the results thereof. The unifying theme of the changes made to the course is to introduce active learning, which has a well-documented positive effect on learning. During the first iteration of the course the new course elements did not increase learning, and we analyze why this was the case. Based on this analysis we made a few changes for the second iteration of the course, and then learning did increase substantially. The basic takeaway is that just giving the students access to elements of active learning is not enough, we must ensure that they use them as intended.
29.	Gran, Ulf, 1973, et al. (författare) Holographic fundamental matter in multilayered media 2019 Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2019:12 Tidskriftsartikel (refereegranskat)abstract We describe a strongly coupled layered system in 3+1 dimensions by means of a top-down D-brane construction. Adjoint matter is encoded in a large-Nc stack of D3-branes, while fundamental matter is confined to (2 + 1)-dimensional defects introduced by a large-Nf stack of smeared D5-branes. To the anisotropic Lifshitz-like background geometry, we add a single flavor D7-brane treated in the probe limit. Such bulk setup corresponds to a partially quenched approximation for the dual field theory. The holographic model sheds light on the anisotropic physics induced by the layered structure, allowing one to disentangle flavor physics along and orthogonal to the layers as well as identifying distinct scaling laws for various dynamical quantities. We study the thermodynamics and the fluctuation spectrum with varying valence quark mass or baryon chemical potential. We also focus on the density wave propagation in both the hydrodynamic and collisionless regimes where analytic methods complement the numerics, while the latter provides the only resource to address the intermediate transition regime.
30.	Gran, Ulf, 1973, et al. (författare) Holographic plasmons 2018 Ingår i: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; 2018:11 Tidskriftsartikel (refereegranskat)abstract Since holography yields exact results, even in situations where perturbation theory is not applicable, it is an ideal framework for modeling strongly correlated systems. We extend previous holographic methods to take the dynamical charge response into account and use this to perform the first holographic computation of the dispersion relation for plasmons. As the dynamical charge response of strange metals can be measured using the new technique of momentum-resolved electron energy-loss spectroscopy (M-EELS), plasmon properties are the next milestone in verifying predictions from holographic models of new states of matter.
31.	Gran, Ulf, 1973, et al. (författare) Holographic response of electron clouds 2019 Ingår i: Journal of High Energy Physics. - : SPRINGER. - 1029-8479 .- 1126-6708. ; 2019:3 Tidskriftsartikel (refereegranskat)abstract In order to make progress towards more realistic models of holographic fermion physics, we use gauge/gravity duality to compute the dispersion relations for quasinormal modes and collective modes for the electron cloud background, i.e. the non-zero temperature version of the electron star. The results are compared to the corresponding results for the Schwarzschild and Reissner-Nordstrom black hole backgrounds, and the qualitative differences are highlighted and discussed.
32.	Gran, Ulf, 1973, et al. (författare) IIB backgrounds with five-form flux 2008 Ingår i: Nuclear Physics B. - : Elsevier BV. - 0550-3213. ; 798:1-2, s. 36-71 Tidskriftsartikel (refereegranskat)abstract We investigate all N=2 supersymmetric IIB supergravity backgrounds with non-vanishing five-form flux. The Killing spinors have stability subgroups $Spin(7)\ltimes\bR^8$, $SU(4)\ltimes\bR^8$ and $G_2$. In the $SU(4)\ltimes\bR^8$ case, two different types of geometry arise depending on whether the Killing spinors are generic or pure. In both cases, the backgrounds admit a null Killing vector field which leaves invariant the $SU(4)\ltimes \bR^8$ structure, and an almost complex structure in the directions transverse to the lightcone. In the generic case, the twist of the vector field is trivial but the almost complex structure is non-integrable, while in the pure case the twist is non-trivial but the almost complex structure is integrable and associated with relatively balanced Hermitian structure. The $G_2$ backgrounds admit a time-like Killing vector field and two spacelike closed one-forms, and the seven directions transverse to these admit a co-symplectic $G_2$ structure. The $Spin(7)\ltimes\bR^8$ backgrounds are pp-waves propagating in an eight-dimensional manifold with holonomy $Spin(7)$. In addition we show that all the supersymmetric solutions of simple five-dimensional supergravity with a time-like Killing vector field, which include the $AdS_5$ black holes, lift to $SU(4)\ltimes\bR^8$ pure Killing spinor IIB backgrounds. We also show that the LLM solution is associated with a co-symplectic co-homogeneity one $G_2$ manifold which has principal orbit $S^3\times S^3$.
33.	Gran, Ulf, 1973, et al. (författare) IIB black hole horizons with five-form flux and extended supersymmetry 2011 Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2011:9 Tidskriftsartikel (refereegranskat)abstract We classify under some assumptions the IIB black hole horizons with 5-form flux preserving more than 2 supersymmetries. We find that the spatial horizon sections with non-vanishing flux preserving 4 supersymmetries are locally isometric either to S(1) x S(3) x T(4) or to S(1) x S(3) x K(3) and the associated near horizon geometries are locally isometric to AdS(3) x S(3) x T(4) and AdS(3) x S(3) x K(3), respectively. The near horizon geometries preserving more than 4 supersymmetries are locally isometric to R(1,1) x T(8).
34.	Gran, Ulf, 1973, et al. (författare) IIB black hole horizons with five-form flux and KT geometry 2011 Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479 .- 1126-6708. ; 2011:5 Tidskriftsartikel (refereegranskat)abstract We investigate the near horizon geometry of IIB supergravity black holes with non-vanishing 5-form flux preserving at least two supersymmetries. We demonstrate that there are three classes of solutions distinguished by the choice of Killing spinors. We find that the spatial horizon sections of the class of solutions with an SU(4) invariant pure Killing spinor are hermitian manifolds and admit a hidden Kahler with torsion (KT) geometry compatible with the SU(4) structure. Moreover the Bianchi identity of the 5-form, which also implies the field equations, can be expressed in terms of the torsion H as d(omega boolean AND H) = partial derivative partial derivative omega(2) = 0, where omega is a Hermitian form. We give several examples of near horizon geometries which include group manifolds, group fibrations over KT manifolds and uplifted geometries of lower dimensional black holes. Furthermore, we show that the class of solutions associated with a Spin(7) invariant spinor is locally a product R-1,R-1 x S, where S is a holonomy Spin(7) manifold.
35.	Gran, Ulf, 1973, et al. (författare) IIB horizons 2013 Ingår i: Classical and Quantum Gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 30:20 Tidskriftsartikel (refereegranskat)abstract We solve the Killing spinor equations for all near-horizon IIB geometries which preserve at least one supersymmetry. We show that generic horizon sections are eight-dimensional almost Hermitian spin(c) manifolds. Special cases include horizon sections with a Spin(7) structure and those for which the Killing spinor is pure. We also explain how the common sector horizons and the horizons with only 5-form flux are included in our general analysis. We investigate several special cases mainly focusing on the horizons with constant scalars admitting a pure Killing spinor and find that some of these exhibit a generalization of the 2-SCYT condition that arises in the horizons with 5-form fluxes only. We use this to construct new examples of near-horizon geometries with both 3-form and 5-form fluxes.
36.	Gran, Ulf, 1973, et al. (författare) IIB solutions with N>28 Killing spinors are maximally supersymmetric 2007 Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479 .- 1126-6708. ; 2007:12, s. 070- Tidskriftsartikel (refereegranskat)abstract We show that all IIB supergravity backgrounds which admit more than 28 Killing spinors are maximally supersymmetric. In particular, we find that for all N>28 backgrounds the supercovariant curvature vanishes, and that the quotients of maximally supersymmetric backgrounds either preserve all 32 or N
37.	Gran, Ulf, 1973, et al. (författare) Index theory and dynamical symmetry enhancement near IIB horizons 2013 Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479 .- 1126-6708. ; 2013:11 Tidskriftsartikel (refereegranskat)abstract We show that the number of supersymmetries of JIB black hole horizons is N = 2N_ + 2 index(D-lambda), where index(D-lambda) is the index of the Dirac operator twisted with the line bundle lambda(1/2) of IIB scalars, and N_ is the dimension of the kernel of a horizon Dirac operator which depends on IIB fluxes. Therefore, all IIB horizons preserve an even number of supersymmetries. In addition if the horizons have non-trivial fluxes and N_ not equal 0, then index(D-lambda) >= 0 and the horizons admit an sl(2,R) symmetry subalgebra. This provides evidence that all such horizons have an AdS/CFT dual. Furthermore if the orbits of sl(2,R) are two-dimensional, the IIB horizons are warped products AdS(2) x(w) S.
38.	Gran, Ulf, 1973, et al. (författare) Invariant Killing spinors in 11D and type II supergravities 2009 Ingår i: Classical and Quantum Gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 26:15 Tidskriftsartikel (refereegranskat)abstract We present all isotropy groups and associated $\Sigma$ groups, up to discrete identifications of the component connected to the identity, of spinors of eleven-dimensional and type II supergravities. The $\Sigma$ groups are products of a Spin group and an R-symmetry group of a suitable lower dimensional supergravity theory. Using the case of SU(4)-invariant spinors as a paradigm, we demonstrate that the $\Sigma$ groups, and so the R-symmetry groups of lower-dimensional supergravity theories arising from compactifications, have disconnected components. These lead to discrete symmetry groups reminiscent of R-parity. We examine the role of disconnected components of the $\Sigma$ groups in the choice of Killing spinor representatives and in the context of compactifications.
39.	Gran, Ulf, 1973, et al. (författare) M-theory backgrounds with 30 Killing spinors are maximally supersymmetric 2010 Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; (March):3, s. (Article Number 112)- Tidskriftsartikel (refereegranskat)abstract We show that all M-theory backgrounds which admit more than 29 Killing spinors are maximally supersymmetric. In particular, we find that the supercovariant curvature of all backgrounds which preserve 30 supersymmetries, subject to field equations and Bianchi identities, vanishes, and that there are no such solutions which arise as discrete quotients of maximally supersymmetric backgrounds.
40.	Gran, Ulf, 1973, et al. (författare) Non-Commutative Open (p,q)-String Theories 2001 Ingår i: JHEP. ; 0111, s. 022 - Tidskriftsartikel (refereegranskat)abstract In this paper we make an SL(2,Z)-covariant generalisation of the noncommutative theories, NCYM and NCOS on the D3-brane, and NCOS on the D5-brane in type IIB. Usually, the noncommutative theories are obtained by studying perturbative F-string theory, and the parameters governing the noncommutative theories are given by the open string data. The S-duality of NCYM and NCOS on the D3-brane has been seen by dualising the background, keeping the F-string under study fixed. We give an SL(2,Z)-covariant generalisation of the open string data relevant when one instead studies perturbative (p,q)-string theory. The S-duality of NCYM and NCOS on the D3-brane is reproduced by instead keeping the background fixed and studying different (p,q)-string theories. We also obtain new noncommutative open (p,q)-string theories on the D3-brane and the D5-brane which are S-dual to ordinary NCOS. The theories are studied using the supergravity duals of the D3-brane and the D5-brane, corresponding to a probe brane in the relevant background.
41.	Gran, Ulf, 1973, et al. (författare) Off-shell structure of twisted (2,0) theory 2014 Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2014:11 Tidskriftsartikel (refereegranskat)abstract A $Q$-exact off-shell action is constructed for twisted abelian (2,0) theory on a Lorentzian six-manifold of the form $M_{1,5} = C\times M_4$, where $C$ is a flat two-manifold and $M_4$ is a general Euclidean four-manifold. The properties of this formulation, which is obtained by introducing two auxiliary fields, can be summarised by a commutative diagram where the Lagrangian and its stress-tensor arise from the $Q$-variation of two fermionic quantities $V$ and $\lambda^{\mu\nu}$. This completes and extends the analysis in [arXiv:1311.3300].
42.	Gran, Ulf, 1973, et al. (författare) On relating multiple M2 and D2-branes 2008 Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479 .- 1126-6708. ; 2008:10 Tidskriftsartikel (refereegranskat)abstract Due to the difficulties of finding superconformal Lagrangian theories for multiple M2-branes, we will in this paper instead focus on the field equations. By relaxing the requirement of a Lagrangian formulation we can explore the possibility of having structure constants fABCD satisfying the fundamental identity but which are not totally antisymmetric. We exemplify this discussion by making use of an explicit choice of a non-antisymmetric fABCD constructed from the Lie algebra structure constants fabc of an arbitrary gauge group. Although this choice of fABCD does not admit an obvious Lagrangian description, it does reproduce the correct SYM theory for a stack of N D2-branes to leading order in gYM−1 upon reduction and, moreover, it sheds new light on the centre of mass coordinates for multiple M2-branes.
43.	Gran, Ulf, 1973, et al. (författare) On supersymmetric anti-de Sitter, de Sitter and Minkowski flux backgrounds 2018 Ingår i: Classical and Quantum Gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 35:6 Tidskriftsartikel (refereegranskat)abstract We test the robustness of the conditions required for the existence of (supersymmetric) warped flux anti-de Sitter, de Sitter, and Minkowski backgrounds in supergravity theories using as examples suitable foliations of anti-de Sitter spaces. We find that there are supersymmetric de Sitter solutions in supergravity theories including maximally supersymmetric ones in 10- and 11-dimensional supergravities. Moreover, warped flux Minkowski backgrounds can admit Killing spinors which are not Killing on the Minkowski subspace and therefore cannot be put in a factorized form.
44.	Gran, Ulf, 1973, et al. (författare) Plasmons in holographic graphene 2020 Ingår i: SciPost Physics. - : SCIPOST FOUNDATION. - 2542-4653. ; 8:6 Tidskriftsartikel (refereegranskat)abstract We demonstrate how self-sourced collective modes - of which the plasmon is a prominent example due to its relevance in modern technological applications - are identified in strongly correlated systems described by holographic Maxwell theories. The characteristic ω ∝ pk plasmon dispersion for 2D materials, such as graphene, naturally emerges from this formalism. We also demonstrate this by constructing the first holographic model containing this feature. This provides new insight into modeling such systems from a holographic point of view, bottom-up and top-down alike. Beyond that, this method provides a general framework to compute the dynamical charge response of strange metals, which has recently become experimentally accessible due to the novel technique of momentum-resolved electron energy-loss spectroscopy (M-EELS). This framework therefore opens up the exciting possibility of testing holographic models for strange metals against actual experimental data.
45.	Gran, Ulf, 1973, et al. (författare) Shear viscosity in interacting two-dimensional Fermi liquids 2023 Ingår i: arXiv:2312.09977. Tidskriftsartikel (refereegranskat)abstract In interaction-dominated two-dimensional electron gases at intermediate temperatures, electron transport is not diffusive as in the conventional Drude picture but instead hydrodynamic. The relevant transport coefficient in this regime is the shear viscosity. Here, we develop a numerically exact basis expansion to solve the Fermi liquid equation, and apply it to compute the shear viscosity of the electron gas with screened Coulomb interactions. Our calculations are valid at all temperatures and in particular describe the response beyond the asymptotic low-temperature limit, where perturbative approaches exist. We show that even in this low-temperature limit, there is a nonanalytic exchange contribution to the shear viscosity, highlighting the need for a full nonperturbative solution of the Fermi liquid equation. We hope that the techniques developed in this work will serve as a platform to determine the response of interacting Fermi liquids.
46.	Gran, Ulf, 1973, et al. (författare) Solution of heterotic Killing spinor equations and special geometry 2009 Ingår i: AIP Conf. Proc. : Proceedings of the Special Metrics and Supersymmetry conference at Universidad del Pais Vasco, May 2008.. ; 1093, s. 144-161 Konferensbidrag (refereegranskat)abstract We outline the solution of the Killing spinor equations of the heterotic supergravity. In addition, we describe the classification of all half supersymmetric solutions.
47.	Gran, Ulf, 1973, et al. (författare) Supersymmetric geometries of IIA supergravity I 2014 Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2014:5, s. Art. no. 024- Tidskriftsartikel (refereegranskat)abstract IIA supergravity backgrounds preserving one supersymmetry locally admit four types of Killing spinors distinguished by the orbits of Spin(9,1) on the space of spinors. We solve the Killing spinor equations of IIA supergravity with and without cosmological constant for Killing spinors representing two of these orbits, with isotropy groups Spin(7) and Spin(7) ⋉ ℝ⁸. In both cases, we identify the geometry of spacetime and express the fluxes in terms of the geometry. We find that the geometric constraints of backgrounds with a Spin(7) ⋉ ℝ⁸ invariant Killing spinor are identical to those found for heterotic backgrounds preserving one supersymmetry.
48.	Gran, Ulf, 1973, et al. (författare) Supersymmetric geometries of IIA supergravity II 2015 Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479 .- 1126-6708. ; 2015:12, s. 1-18 Tidskriftsartikel (refereegranskat)abstract We solve the Killing spinor equations of standard and massive IIA supergravities for a Killing spinor whose isotropy subgroup in Spin(9, 1) is SU(4) and identify the geometry of the spacetime. We demonstrate that the Killing spinor equations impose some mild constraints on the geometry of the spacetime which include the existence of a time-like Killing vector field which leaves the fields and the Killing spinor invariant.
49.	Gran, Ulf, 1973, et al. (författare) Supersymmetric geometries of IIA supergravity III 2016 Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2016:6 Tidskriftsartikel (refereegranskat)abstract We find that (massive) IIA backgrounds that admit a G2? ?8 invariant Killing spinor must exhibit a null Killing vector field which leaves the Killing spinor invariant and that the rotation of the Killing vector field satisfies a certain g2 instanton condition. This result together with those in [4] and [5] complete the classification of geometries of all (massive) IIA backgrounds that preserve one supersymmetry. We also explore the geometry of a class of backgrounds which admit a G2? ?8 invariant Killing spinor and where in addition an appropriate 1-form bilinear vanishes. In all cases, we express the fluxes of the theory in terms of the geometry.
50.	Gran, Ulf, 1973, et al. (författare) Supersymmetric heterotic string backgrounds 2007 Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 656:1-3, s. 119-126 Tidskriftsartikel (refereegranskat)abstract We present the main features of the solution of the gravitino and dilatino Killing spinor equations derived in hep-th/0510176 and hep-th/0703143 which have led to the classification of geometric types of all type I backgrounds. We then apply these results to the supersymmetric backgrounds of the heterotic string. In particular, we solve the gaugino Killing spinor equation together with the other two Killing spinor equations.

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