** Books **

* - Extremals of the Sobolev inequality and the quaternionic
contact Yamabe problem*, (with D. Vassilev), World Scientific
Publishing Co. Pte. Ltd., Hackensack, NJ, 2011. xviii+219 pp.

* - Quaternionic contact Einstein structures and quaternionic
contact Yamabe problem*, (with I. Minchev and D. Vassilev),
Memoirs Amer. Math. Soc. (2014), **231**, no. 1086.
** Survey papers **

* - The Lichnerowicz and Obata first eigenvalue theorems and
the Obata uniqueness result in the Yamabe problem on CR and
quaternionic contact manifolds*, (with Dimiter Vassilev),
Nonlinear Analysis - Theory **126** (2015), 262-323.
arXiv:1504.03259.
**Papers**

* - Quaternionic contact hypersurfaces in hyper-K\"ahler
manifolds*, (with Ivan Minchev, Dimiter Vassilev), to appear in Annali di
matematica Pura ed Applicata.
arXiv:1406.4256.

* - Quaternionic contact Einstein manifolds *, (with Ivan
Minchev and Dimiter Vassilev), to appear in Math. Research Letters.
arXiv:1306.0474.

* - Connections on non-symmetric (generalized) Riemannian manifold and gravity*,
(with Milan Zlatanovic), to appear in Class. Quntum Gravity.
arXiv:1503.05217.

* - The Obata sphere theorems on a quaternionic contact
manifold of dimension bigger than seven *, (with Alexander Petkov
and Dimiter Vassilev), to appear in J. Spectral Theory.
arXiv:1303.0409.

* - The quaternionic Heisenberg group and Heterotic String
Solutions with non-constant dilaton in dimensions 7 and 5 *, (with
Marisa Fernandez, Luis Ugarte, Dimiter Vassilev), Comm. Math. Phys. **339**
(2015), no. 1, 199–219.
arXiv:arXiv:1410.4130.

* - Non-Kaehler Heterotic String Solutions with non-zero fluxes
and non-constant dilaton* , (with Marisa Fernandez, Luis Ugarte,
Dimiter vassilev), J. High Energy Physics (JHEP) 06 (2014) 073;
arXiv:arXiv:1402.6107.

* - Vanishing theorems on $(l|k)$-strong Kaehler manifolds with
torsion*, (with George Papadopoulos), Adv. Math.
**237** (2013), 147-164.
arXiv: arXiv:1202.6470 .

* - An Obata type result for the first eigenvalue of the
sub-Laplacian on a CR manifold with a divergence free torsion *,
(with Dimiter Vassilev), J. Geom **103**, 3 (2012),
475-504.
arXiv: arXiv:1203.5812.

* - An Obata-type theorem on a three-dimensional CR
manifold*,(with Dimiter Vassilev), Glasgow Math. J.,
**56** (2014), 283-294.
arXiv: arXiv:1208.1040.

* - The sharp lower bound of the first eigenvalue of the
sub-Laplacian on a quaternionic contact manifold in dimension
seven * (with Alexander Petkov and Dimiter Vassilev),
Nonlinear Analysis-Theory, **93** (2013), 51-61.
arXiv:arXiv:1210.6932.

* - The sharp lower bound of the first eigenvalue of the sub-Laplacian on a
quaternionic contact manifold *,
(with Alexander Petkov and Dimiter Vassilev), J. Geom. Analysis, **24**
(2014), no. 2, 595-612.
arXiv:arXiv:1112.0779.

*- The optimal constant in the $L^2$ Folland-Stein inequality on the quaternionic Heisenberg group*,
(with I. Minchev and D. Vassilev), Ann. Sc. Norm. Super. Pisa Cl. Sci. **(5) Vol. XI ** (2012), 635-652;
arXiv:arXiv:1009.2978.

*- Quaternionic Kaehler and Spin(7) metrics arising from quaternionic contact Einstein structures*,
(with L. C. de Andres, M. Fernandez, J. A. Santisteban, L. Ugarte and D. Vassilev), Annali di
matematica Pura ed Applicata, **193**, 1 (2014), 261-290.
arXiv:arXiv:1009.2745.

*- Bianchi type A hyper-symplectic and hyper-K\"ahler metrics in 4D *, (with
Luis C. de Andre's, Marisa Ferna'ndez, Jose A. Santisteban, Luis Ugarte and Dimiter Vassilev),
Class. Quant. Grav. **29** (2012), 025003.
arXiv:arXiv:1102.1518.

*- Compact supersymmetric solutions of the heterotic equations of motion
in dimensions 7 and 8*, (with M. Ferna'ndez, L. Ugarte and R. Villacampa),
Adv. Theor. Math. Phys., (2011) **15**, 245-284.
arXiv:0806.4356.

*- HKT manifolds with holonomy SL(n,H)*,
(with A. Petkov), International Mathematics Research Notices, 2012, **16**, 3779--3799;
arXiv:arXiv:1010.5052.

*- The twistor space of a quaternionic contact manifold*,
(with J. Davidov and I. Minchev), Quart. J. Math. **63** (2012), no. 4,
873-890.
arXiv:arXiv:1010.4994.

*- Heterotic supersymmetry, anomaly cancellation and equations of motion,*
Phys. Lett. **B685** (2010), 190-196.
arXiv:0908.2927.

*- Quaternionic contact manifolds with a closed fundamental 4-form*,
(with D. Vassilev), Bull. London Math. Soc., **42** (6) (2010), 1021–1030.
arXiv:0810.3888,.

*- Conformal quaternionic contact curvature and the local sphere theorem,*
(with D. Vassilev), Journal de Mathe'matiques Pures et Applique'es (JMPA) **93** (2010), 277-307.
arXiv:0707.1289.

*- Extremals for the Sobolev inequality on the seven dimensional
quaternionic Heisenberg group and the quaternionic contact
Yamabe problem*, (with I. Minchev and D. Vassilev), J. Eur. Math. Soc. (JEMS) **12** (2010), 1041–1067.
math.DG/0703044

*- Compact supersymmetric solutions of the heterotic equations of motion
in dimension 5*, (with M. Ferna'ndez, L. Ugarte and R. Villacampa), Nuclear Physics **B820** (2009), 483-502.
arXiv:0811.2137.

*- Non-Kaehler Heterotic String Compactifications with non-zero fluxes
and constant dilaton*, (with M. Ferna'ndez, L. Ugarte and R. Villacampa),
Comm. Math. Phys. **288** (2009), 677-697.
arXiv:0804.1648

*- Conformal Paracontact curvature and the local flatness theorem*,
(with D. Vassilev and S. Zamkovoy), Geom. Dedicata ** 144** (2010), 79-100.
arXiv:0707.3773

*- Curvature decomposition of $G_2$ manifolds* (with R. Cleyton),
J. Geom. Phys. **58** (2008), 1429-1449.
math.DG/0702289.

*- Nearly hypo structures and compact Nearly K\"ahler 6-manifolds with
conical singularities*
(with M. Fernandez, V. Munos and L. Ugarte), J. London Math. Soc. **78** (2008), 580-604.
math.DG/0602160.

*- Conformal equivalence between certain geometries in dimension
6 and 7*, (with R. Cleyton), Math. Res. Lett. **15** (2008), 631-641.
math.DG/0607487.

*- Twistor and Reflector Spaces of Almost Para-Quaternionic Manifolds*,
(with I. Minchev and S. Zamkovoy), to
appear in "Handbook of pseudo-Riemannian Geometry and
Supersymmetry" to be published by the European Mathematical
Society EMS in the series IRMA Lectures in Mathematics and
Theoretical Physics.
math.DG/0511657.

*- SU(3)-structures on submanifolds of a Spin(7)-manifold*,
(with F. Martin Cabrera), Diff. Geom. Appl. **26** (2008), 113-132.
math.DG/0510406.

*- On the geometry of closed $G_2$-structures*, (with R.
Cleyton), Commun. Math. Phys., **270** (2007), 53--67.
math.DG/0306362.

*- Locally conformal parallel $G_2$ and $Spin(7)$ manifolds*,
(with M. Parton and P. Piccinni), Math. Res. Lett., **13** (2006), 167--177.
math.DG/0509038.

*- Hyper-ParaHermitian manifolds with torsion*, (with V. Tsanov and S. Zamkovoy), J. Geom. Phys. **56**, (2006), 670-690.
math.DG/0405585.

*- Para-Hermitian and Para-Quaternionic manifolds*, (with S. Zamkovoy), Diff. Geom. Appl. **23** (2005), 205-234.
math.DG/0310415.

*- $SU(3)$-instantons and $G_2, Spin(7)$ heterotic string solitons*, (with P. Ivanov), Commun. Math. Phys. **259** (2005), 79-102.
math.DG/0312094.

*- Connection with torsion, parallel spinors and geometry of Spin(7) manifolds*, Math. Res. Lett. **11** (2004), 171--186.
math.DG/0111216.

*- Quaternionic K\"ahler and hyperK\"ahler manifolds with torsion and twistor spaces*, (with I. Minchev), J. reine angew. Math. **567** (2004), 215-233,
math.DG/0112157.

*- Deformations of generalized calibrations and compact non-Kahler
manifolds with vanishing first Chern class*, (with J. Gutowski and
G. Papadopoulos), Asian J. Math. **7** (2003), 39-80,
math.DG/0205012.

*- Almost contact manifolds, connections with torsion, and parallel spinors*, (with Th. Friedrich), J. reine angew. Math.
**559** (2003), 217-236,
math.DG/0111131.

*- Killing spinor equations in dimension 7 and geometry of integrable $G_2$ manifolds*, (with Th. Friedrich), J. Geom. Phys.
**48** (2003), 1-11,
math.DG/0112201

*- Weyl structure with positive Ricci tensor*, (with B. Alexandrov), Diff. Geom. Appl. **18** (2003), 343-350,
math.DG/9902033.

*- Parallel spinors and connections with skew-symmetric torsion in string theory*, (with Th. Friedrich), Asian J. Math. **6** (2002), 303-336,
math.DG/0102142.

*- Geometry of Quaternionic Kaehler connections with
torsion*, J. Geom. Phys. **41** (2002), 235-257,
math.DG/0003214.

*- A no-go theorem for string warped compactification*, (with G.Papadopoulos), Phys. Lett. **B 497** (2001) 309-316,
hep-th/0008232.

*- Vanishing theorems and String Backgrounds*, (with G.Papadopoulos), Class. Quantum Gravity **18** (2001), 1089-1110,
math.DG/0010038.

*- Harmonic spinors of Dirac operator of connection with torsion in dimension 4*, (with P.Dalakov), Class. Quantum Gravity **18** (2001), 253-265, [PS]

*- Vanishing theorems on Hermitian manifolds*, (with B. Alexandrov), Diff. Geom. Appl. **14** (3) (2001), 251-265,
math.DG/9901090.

*- The Dolbeault operator on Hermitian spin surfaces*, (with. B. Alexandrov and G. Grantcharov), Ann. Inst. Fourier (Grenoble) **51** 1 (2001), 221-235,
math.DG/9902005.

*- Harmonic and holomorphic 1-forms on compact balanced Hermitian manifold* (with G.Ganchev), Diff. Geom. Appl. **14** (1) (2001), 79-93. [PS]

*- Holomorphic and Killing vector fields on compact balanced
Hermitian manifolds*, (with G.Ganchev), Int. J. Math. **11** (2000), 15-28. [PS]

*- Dirac operators on Hermitian spin surfaces* (with B. Alexandrov), Ann. Glob. Anal. Geom. **18** (2000), 529-539.
[PS]

*- Einstein-Weyl structures on certain compact conformal
manifolds*, Quart. J. Math. (Oxford) (2) **50** (1999), 457-462. [PS]

*- Orthogonal complex structures on certain Riemannian 6-manifolds*, (with V. Apostolov and G. Grantcharov), Diff. Geom. Appl. **11** (1999) 279-296. [PS]

*- Riemannian manifold in which the skew-symmetric curvature
operator has pointwise constant eigenvalues*, (with I.Petrova),
Geom. Dedicata **70** (1998), 269-282. [PS]

*- Curvature properties of twistor spaces of quaternionic Kaehler manifolds*, (with B. Alexandrov and G. Grantcharov), J. Geom. **62** (1998), 1-12. [PS]

*- An estimate for the first eigenvalue of the Dirac operator on compact Riemannian spin manifold admitting parallel one form*,
(with B. Alexandrov and G. Grantcharov), J. Geom. Phys. **28** (1998), 263-270. [PS]

*- Hermitian structures on twistor spaces*, (with V. Apostolov and G. Grantcharov), Ann. Glob. Anal. Geom. **16** (1998), 291-308. [PS]

*- Compact Hermitian surfaces of constant antiholomorphic
sectional curvature*, (with V.Apostolov and G.Ganchev), Proc.
Amer. Math. Soc. **125** (1997), 3705-3714. [PS]

*- Einstein-Hermitian surfaces and Hermitian Einstein-Weyl
structures in dimension 4*, (with P.Gauduchon), Mathematische
Zeitschrift **226** (1997), 317-326. [PS]

*- On the fundamental theorem for non-degenerate complex affine hypersurface immersions*, Monatshefte Mathematics **123** (1997), 321-336. [PS]

*- Riemannian manifolds in which certain curvature operator has constant eigenvalues along each circle*, (with I.Petrova),
Ann. Glob. Anal. Geom. **15** (1997), 157-171. [PS]