. Proof and . Let, By Proposition 7.3.5 and Proposition 7.3.1, M admits a complex structure J such that (M, J, g) is a Hermitian manifold. Now, if (M, J, g) is a Hermitian manifold, by Proposition 7.3.5, the canonical Spin c structure on M admits a pure spinor field ? ? ?(? 0 M ) By Proposition 7.3.1 and since J is a complex structure, the pure spinor field is integrable. Hence, the first two statements are equivalent. The last two statements are also equivalent because if (M, J, g) is a Hermitian manifold with a complex structure J, the eigenbundle T 1,0 M of T M ? C corresponding to the eigenvalue i of J gives the desired almost CR-structure of type ( n 2 = m, 0) Because T 1,0 M is integrable, the almost CR-structure is a CR-structure of type (m, 0) Conversely, a Riemannian manifold having a CR-structure of type (m, 0) is a complex manifold, p.121

M. Atiyah and N. , Hitchin and I. Singer, Self-duality in four-dimensional Riemannian geometry, Proc. Roy. Soc. London A 362, pp.425-461, 1978.

]. T. Aub82 and . Aubin, Nonlinear Analysis on Manifolds, Monge-Ampre Equations, 1982.

C. Bär, Lower eigenvalue estimates for Dirac operators, Math. Ann, vol.239, pp.39-46, 1992.

P. [. Bär, A. Gauduchon, and . Moroianu, Generalized cylinders in semi-Riemannian and spin geometry, Mathematische Zeitschrift, vol.15, issue.3, pp.545-580, 2005.
DOI : 10.1007/s00209-004-0718-0

C. Bär, Spectral bounds for Dirac operators on open manifolds, Annals of Global Analysis and Geometry, vol.340, issue.1, pp.67-79, 2009.
DOI : 10.1007/s10455-008-9149-1

]. H. Baum81 and . Baum, Spin-Strukturen und Dirac-OperatorenüberOperatoren¨Operatorenüber pseudoriemannschen Mannigfaltigkeiten, 1981.

H. Baum, Eigenvalue estimates for Dirac operators coupled to instantons, Annals of Global Analysis and Geometry, vol.102, issue.1, pp.193-209, 1994.
DOI : 10.1007/BF02108297

]. F. Bibliography-[-bon02 and . Bonahon, Geometric structures on 3-manifolds, In Handbook of geometric topology, pp.93-164, 2002.

P. [. Bourguignon and S. Gauduchon, Spineurs, op??rateurs de dirac et variations de m??triques, Communications in Mathematical Physics, vol.XXVIII, issue.Suppl. 1, pp.581-599, 1992.
DOI : 10.1007/BF02099184

O. [. Bourguignon, J. L. Hijazi, A. Milhorat, and . Moroianu, A spinorial approach to Riemannian and conformal geometry, Monograph

]. C. Boyer06, K. Boyer, P. Galicki, and . Matzeu, On Eta-Einstein Sasakian Geometry, Communications in Mathematical Physics, vol.262, issue.1, pp.177-208, 2006.
DOI : 10.1007/s00220-005-1459-6

]. T. Bran00 and . Branson, Kato constants in Riemannian geometry, Math. Res. Lett, vol.7, pp.245-262, 2000.

P. [. Calderbank, M. Gauduchon, and . Herzlich, Refined Kato Inequalities and Conformal Weights in Riemannian Geometry, Journal of Functional Analysis, vol.173, issue.1, pp.214-255, 2000.
DOI : 10.1006/jfan.2000.3563

URL : https://hal.archives-ouvertes.fr/hal-00987720

]. E. Cart66 and . Cartan, The theory of spinors, 1966.

J. Dadok and R. Harvey, Calibrations on R 6 , Duke Math, J, vol.4, pp.1231-1243, 1983.

. B. Dhm, L. Daniel, P. Hauswirth, and . Mira, Constant mean curvature surfaces in homogeneous 3-manifolds

]. S. Don96 and . Donaldson, The Seiberg-Witten equations and 4-manifold topology, Bull. Amer. Math. Soc, vol.33, pp.45-70, 1996.

G. [. Dragomir and . Tomassini, Differential geometry and analysis on CRmanifolds , Progress in mathematics

]. T. Fri80 and . Friedrich, Der erste Eigenwert des Dirac-operators einer kompakten Riemannschen Mannigfaltigkeit nichtnegativer Skalarkrümmung, Math. Nach, vol.97, pp.117-146, 1980.

. Fri98 and . ???, On the spinor representation of surfaces in Euclidean 3-spaces, J. Geom. Phys, vol.28, pp.143-157, 1998.

E. [. Friedrich and . Kim, Dirac operator's in Riemannian Geometry, Graduate studies in mathematics The Einstein-Dirac equation on Riemannian Spin manifolds, J. Geom. Phys, vol.25, pp.33-128, 2000.

[. ???, Some remarks on the Hijazi inequality and generalizations of the Killing equation for spinors, J. Geom. Phys, vol.37, pp.1-14, 2001.

]. N. Gi-mo00, B. Ginoux, and . Morel, On eigenvalue estimates for the submanifold Dirac operator, Int. J. Math, vol.13, issue.5, pp.533-548, 2002.

]. Gin09 and . ???, The Dirac spectrum, Lect. Notes in Math, 1976.

G. [. Ginoux and . Habib, A spectral estimate for the Dirac operator on Riemannian flows, Central European Journal of Mathematics, vol.8, issue.5, 2010.
DOI : 10.2478/s11533-010-0060-1

URL : https://hal.archives-ouvertes.fr/hal-00523746

M. J. Gursky and C. Lebrun, Yamabe Invariants and $ Spin^c $ Structures, Geometric And Functional Analysis, vol.8, issue.6, pp.965-977, 1998.
DOI : 10.1007/s000390050120

]. N. Nad06 and . Grosse, On a conformal invariant of the Dirac operator on noncompact manifolds, Ann. Glob. Anal. Geom, vol.30, pp.407-416, 2006.

. Nad08b and . ???, The Hijazi inequality in conformally parabolic manifolds, 2008.

G. Habib, Energy???momentum tensor on foliations, Journal of Geometry and Physics, vol.57, issue.11, pp.2234-2248, 2007.
DOI : 10.1016/j.geomphys.2007.07.002

URL : https://hal.archives-ouvertes.fr/hal-00159103

]. G. Hab-roth10, J. Habib, and . Roth, Skew Killing spinors, 2010.

]. G. Ha-na10, R. Habib, and . Nakad, The energy-momentum tensor on low dimensional Spin c manifolds, 2010.

R. [. Hererra and . Nakad, Spin c characterization of CR-structures, 2011.

M. Herzlich and A. Moroianu, Generalized Killing spinors and conformal eigenvalue estimates for Spin c manifold, Annals of Global Analysis and Geometry, vol.17, issue.4, pp.341-370, 1999.
DOI : 10.1023/A:1006546915261

O. Hijazi, Opérateurs de Dirac sur les variétés riemanniennes : minoration des valeurs propres, 1984.

. Hij91 and . ???, Premì ere valeur propre de l'opérateur de Dirac et nombre de Yamabe, C. R. Acad. Sci. Paris, t, vol.313, pp.865-868, 1991.

. Hij95 and . ???, Lower bounds for the eigenvalues of the Dirac operator, J. Geom. Phys, vol.16, pp.27-38, 1995.

[. ???, Conformal lower bounds for the Dirac operator on embedded hypersurfaces, Asian J. Math, vol.6, pp.23-36, 2002.

S. [. Hijazi, S. Montiel, and . Roldán, Eigenvalue Boundary Problems for the Dirac Operator, Communications in Mathematical Physics, vol.231, issue.3, pp.375-390, 2002.
DOI : 10.1007/s00220-002-0725-0

S. [. Hijazi, F. Montiel, and . Urbano, Spinc geometry of K??hler manifolds and the Hodge Laplacian on minimal Lagrangian submanifolds, Mathematische Zeitschrift, vol.7, issue.4, pp.821-853, 2006.
DOI : 10.1007/s00209-006-0936-8

]. K. Kir86 and . Kirchberg, An estimation for the first eigenvalue of the Dirac operator on closed Kähler manifolds of positive scalar curvature, Ann. Glob. Anal. Geom, vol.3, pp.291-325, 1986.

]. K. Kir90 and . Kirchberg, The first eigenvalue of the Dirac operator on Kähler manifolds, J. Geom. Phys, vol.4, pp.449-468, 1990.

P. Kronheimer and T. Mrowka, The Genus of Embedded Surfaces in the Projective Plane, Mathematical Research Letters, vol.1, issue.6, pp.797-808, 1994.
DOI : 10.4310/MRL.1994.v1.n6.a14

]. R. Ku-sc, N. Kusner, and . Schmitt, The spinor representation of surfaces in space, ArXiv:dg-ga, 9610005.

C. Lebrun, Einstein metrics and Mostow rigidity, Mathematical Research Letters, vol.2, issue.1, pp.1-8, 1995.
DOI : 10.4310/MRL.1995.v2.n1.a1

J. Milnor, Curvatures of left invariant metrics on lie groups, Advances in Mathematics, vol.21, issue.3, pp.293-329, 1976.
DOI : 10.1016/S0001-8708(76)80002-3

]. B. Mor01 and . Morel, Eigenvalue estimates for the Dirac-Schrödinger operators, J. Geom. Phys, vol.38, pp.1-18, 2001.

. Mor05 and . ???, Surfaces in S 3 and H 3 via spinors, Actes du séminaire de théorie spectrale et géométrie, pp.9-22, 2005.

]. S. Mon85 and . Montiel, Real hypersurfaces of a complex hyperbolic space, J. Math. Soc. Japan, p.37, 1985.

]. Mon05 and . ???, Using spinors to study submanifolds, 2004.

]. A. Moro96 and . Moroianu, Opérateur de Dirac et submersions riemanniennes, 1996.

]. R. Nak10 and . Nakad, Lower bounds for the eigenvalues of the Dirac operator on Spin c manifolds, J. Geom. Phys, vol.60, pp.1634-1642, 2010.

. Nak11a and . ???, The energy-momentum tensor on Spin c manifolds, 2011.

. Nak11b and . ???, The Hijazi inequalities on complete Riemannian Spin c manifold, Advances in Mathematical Physics, vol.2011, 2011.

J. [. Nakad and . Roth, Hypersurfaces of Spin c manifolds and Lawson correspondence, 2011.

]. R. Pen75 and . Penrose, Twistor theory, its aims and achievements, Quantum Gravity: an Oxford Symposium, pp.268-407, 1975.

]. R. Pen86a, W. Penrose, and . Rindler, Spinors and space-time, 1986.

R. Petit, <mml:math altimg="si1.gif" overflow="scroll" xmlns:xocs="http://www.elsevier.com/xml/xocs/dtd" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.elsevier.com/xml/ja/dtd" xmlns:ja="http://www.elsevier.com/xml/ja/dtd" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:tb="http://www.elsevier.com/xml/common/table/dtd" xmlns:sb="http://www.elsevier.com/xml/common/struct-bib/dtd" xmlns:ce="http://www.elsevier.com/xml/common/dtd" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:cals="http://www.elsevier.com/xml/common/cals/dtd"><mml:msup><mml:mi mathvariant="normal">Spin</mml:mi><mml:mi>c</mml:mi></mml:msup></mml:math>-structures and Dirac operators on contact manifolds, Differential Geometry and its Applications, vol.22, issue.2, pp.229-252, 2005.
DOI : 10.1016/j.difgeo.2005.01.003

]. P. Sco83 and . Scott, The geometry of 3-manifolds, Bull. Lond, Math. Soc, vol.15, issue.5, pp.401-487, 1983.

D. [. Piccione and . Tausk, An existence theorem for $G$-structure preserving affine immersions, Indiana University Mathematics Journal, vol.57, issue.3, pp.1431-1465, 2008.
DOI : 10.1512/iumj.2008.57.3281

H. Rosenberg, Minimal surfaces in M 2 × R, Illinois J. Math, vol.46, pp.1177-1195, 2002.

J. Roth, Rigidité des hypersurfaces en géométrie riemannienne et spinorielle : aspect extrinsèque et intrinsèque, 2006.

]. P. Somm76 and . Sommers, Properties of shear-free congruences of null geodesics, Proceeding of the Royal Society of London A, vol.349, pp.309-318, 1976.

]. Y. Ta63, S. Tashiro, and . Tachibana, On Fubinian and C-Fubinian manifolds, K¯ odai Math. Sem. Rep, vol.15, pp.176-183, 1963.

]. E. Wit94 and . Witten, Monopoles and four-manifolds, Math. Res. Lett, vol.1, pp.769-796, 1994.