Publications (100)261.37 Total impact
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ABSTRACT: Recently modified gravitational theories which mimic the behaviour of dark matter, the socalled "Mimetic Dark Matter", have been proposed. We study the consistency of such theories with respect to the absence of ghost instability and propose a new tensorvectorscalar theory of gravity, which is a generalization of the previous models of mimetic dark matter with additional desirable features. In the light of these observations, the idea of mimetic matter is a promising approach to the problem of dark matter.04/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Among modified gravitational theories, the TensorVectorScalar (TeVeS) occupies a special place  it is a covariant theory of gravity that produces the modified Newtonian dynamics (MOND) in the nonrelativistic weak field limit and explains the astrophysical data by all means better than the GR, at scales larger than that of the Solar System. We show that, in contrast with other modified theories, TeVeS is free from ghosts. These achievements make TeVeS (and its nonrelativistic limit) a viable theory of gravity. A speculative outlook on the emergence of TeVeS from a quantum theory is presented.02/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We construct a model unifying gravity with weak $SU(2)$ gauge and "Higgs" scalar fields. We assume the existence of a visible and an invisible (hidden) sector of the Universe. We used the extension of Plebanski's 4dimensional gravitational theory, in which the fundamental fields are twoforms containing tetrads, spin connections and additional auxiliary fields. Considering a $Spin(4,4)$ invariant extended Plebanski action, we recover the actions in both (visible and invisible) sectors of the Universe. After symmetry breaking of the graviweak (GW) unification, its physical constants (Newton's constants, cosmological constants, YMcouplings, etc.), are determined by a parameter $g_{uni}$ of the GW unification. It is discussed that if this "Higgs" field coming in the GW unification could be the Higgs of the Standard Model, then the idea that its vacuum value could be, according to the Multiple Point Principle, a second minimum of the Higgs field effective potential, turns out not to be viable. Then other scalar "Higgs" field, giving the inflation and axion fields, has a Planck scale expectation value, and could have a better chance of being the scalar field unified with gravity.11/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We analyze gravitational theories with quadratic curvature terms, including the case of conformally invariant Weyl gravity, motivated by the intention to find a renormalizable theory of gravity in the ultraviolet region, yet yielding general relativity at long distances. In the Hamiltonian formulation of Weyl gravity, the number of local constraints is equal to the number of unstable directions in phase space, which in principle could be sufficient for eliminating the unstable degrees of freedom in the full nonlinear theory. All the other theories of quadratic type are unstable  a problem appearing as ghost modes in the linearized theory. We find that the full projection of the Weyl tensor onto a threedimensional hypersurface contains an additional fully traceless component, given by a quadratic extrinsic curvature tensor. A certain inconsistency in the literature is found and resolved: when the conformal invariance of Weyl gravity is broken by a cosmological constant term, the theory becomes pathological, since a constraint required by the Hamiltonian analysis imposes the determinant of the metric of spacetime to be zero. In order to resolve this problem by restoring the conformal invariance, we introduce a new scalar field that couples to the curvature of spacetime, reminiscent of the introduction of vector fields for ensuring the gauge invariance.11/2013; 89(6).  [Show abstract] [Hide abstract]
ABSTRACT: The CPT theorem in quantum field theory, its validity, breaking and consequences are reviewed. One can show that for CPT theorem to hold, Lorentz invariance is not always needed. Also one can have CPT violation, while there is Lorentz invariance. Field theoretical examples for both cases are given and mass differences between particleantiparticle are discussed as well. Unambiguous tests of CPT violation, unrelated to the breaking of Lorentz invariance, are suggested.Journal of Physics Conference Series 11/2013; 474(1):2031.  [Show abstract] [Hide abstract]
ABSTRACT: We study Mtheory and Dbrane quantum partition functions for microscopic black hole ensembles within the context of the AdS/CFT correspondence in terms of highest weight representations of infinitedimensional Lie algebras, elliptic genera, and Hilbert schemes, and describe their relations to elliptic modular forms. The common feature in our examples lie in the modular properties of the characters of certain representations of the pertinent affine Lie algebras, and in the role of spectral functions of hyperbolic threegeometry associated with qseries in the calculation of elliptic genera. We present new calculations of supergravity elliptic genera on local CalabiYau threefolds in terms of BPS invariants and spectral functions, and also of equivariant Dbrane elliptic genera on generic toric singularities. We use these examples to conjecture a link between the black hole partition functions and elliptic cohomology.08/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We consider a Graviweak Unification model with the assumption of the existence of the hidden (invisible) sector of our Universe parallel to the visible world. This Hidden World (HW) is assumed to be a Mirror World (MW) with broken mirror parity. We start with a diffeomorphism invariant theory of a gauge field valued in a Lie algebra g, which is broken spontaneously to the direct sum of the spacetime Lorentz algebra and the YangMills algebra: $\tilde {\mathfrak g} = {\mathfrak su}(2)^{(grav)}_L \oplus {\mathfrak su}(2)_L$  in the ordinary world, and $\tilde {\mathfrak g}' = {{\mathfrak su}(2)'}^{(grav)}_R \oplus {\mathfrak su}(2)'_R$  in the hidden world. Using an extension of the Plebanski action for general relativity, we recover the actions for gravity, SU(2) YangMills and Higgs fields in both (visible and invisible) sectors of the Universe, and also the total action. After symmetry breaking, all physical constants, including the Newton's constants, cosmological constants, YangMills couplings, and other parameters, are determined by a single parameter $g$ presented in the initial action, and by the Higgs VEVs. The Dark Energy problem of this model predicts a too large supersymmetric breaking scale ($\sim 10^{10}10^{12}$ GeV), which is not within the reach of the LHC experiments.International Journal of Modern Physics A 07/2013; 28(18):1350085. · 1.13 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study a Lie algebra of formal vector fields $W_n$ with its application to the perturbative deformed holomorphic symplectic structure in the Amodel, and a CalabiYau manifold with boundaries in the Bmodel. A relevant concept in the vertex operator algebra and the BRST cohomology is that of the elliptic genera (the oneloop string partition function). We show that the elliptic genera can be written in terms of spectral functions of the hyperbolic threegeometry (which inherits the cohomology structure of BRSTlike operator). We show that equivalence classes of deformations are described by a Hochschild cohomology theory of the DGalgebra ${\mathfrak A} = (A, Q)$, $Q =\bar{\partial}+\partial_{\rm deform}$, which is defined to be the cohomology of $(1)^n Q +d_{\rm Hoch}$. Here $\bar{\partial}$ is the initial nondeformed BRST operator while $\partial_{\rm deform}$ is the deformed part whose algebra is a Lie algebra of linear vector fields ${\rm gl}_n$. We discuss the identification of the harmonic structure $(HT^\bullet(X); H\Omega_\bullet(X))$ of affine space $X$ and the group ${\rm Ext}_{X}^n({\cal O}_{\triangle}, {\cal O}_{\triangle})$ (the HKR isomorphism), and bulkboundary deformation pairing.International Journal of Modern Physics A 06/2013; 28(16). · 1.13 Impact Factor 
Article: Quantum Corrections to BekensteinHawking Black Hole Entropy and Gravity Partition Functions
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ABSTRACT: Algebraic aspects of the computation of partition functions for quantum gravity and black holes in $AdS_3$ are discussed. We compute the subleading quantum corrections to the BekensteinHawking entropy. It is shown that the quantum corrections to the classical result can be included systematically by making use of the comparison with conformal field theory partition functions, via the $AdS_3/CFT_2$ correspondence. This leads to a better understanding of the role of modular and spectral functions, from the point of view of the representation theory of infinitedimensional Lie algebras. Besides, the sum of known quantum contributions to the partition function can be presented in a closed form, involving the PattersonSelberg spectral function. These contributions can be reproduced in a holomorphically factorized theory whose partition functions are associated with the formal characters of the Virasoro modules. We propose a spectral function formulation for quantum corrections to the elliptic genus from supergravity states.Nuclear Physics B 04/2013; 873(3). · 4.33 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: An attempt is made to incorporate the electromagnetic interaction in a Lorentz invariant but CPT violating nonlocal model with particleantiparticle masssplitting, which is regarded as a modified QED. The gauge invariance is maintained by the Schwinger nonintegrable phase factor but the electromagnetic interaction breaks C, CP and CPT symmetries. Implications of the present CPT breaking scheme on the electromagnetic transitions and particleantiparticle pair creation are discussed. The CPT violation such as the one suggested here may open a new path to the analysis of baryon asymmetry since some of the Sakharov constraints are expected to be modified.Physics Letters B 09/2012; 718(s 4–5). · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The Lorentz invariant $CPT$ violation by using nonlocal interactions is naturally incorporated in the Higgs coupling to neutrinos in the Standard Model, without spoiling the basic $SU(2)_{L}\times U(1)$ gauge symmetry. The neutrinoantineutrino mass splitting is thus realized by the mechanism which was proposed recently, assuming the neutrino masses to be predominantly Diractype in the Standard Model.Physics Letters B 08/2012; 718(1). · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In order to explore some general features of modified theories of gravity which involve higher derivatives and spontaneous Lorentz and/or diffeomorphism symmetry breaking, we study the recently proposed new version of covariant renormalizable gravity (CRG). CRG attains powercounting renormalizability via higher derivatives and introduction of a constrained scalar field and spontaneous symmetry breaking. We obtain an ArnowittDeserMisner representation of the CRG action in fourdimensional spacetime with respect to a foliation of spacetime adapted to the constrained scalar field. The resulting action is analyzed by using Hamiltonian formalism. We discover that CRG contains two extra degrees of freedom. One of them carries negative energy (a ghost) and it will destabilize the theory due to its interactions. This result is in contrast with the original paper [Phys. Lett. B 701, 117 (2011), arXiv:1104.4286 [hepth]], where it was concluded that the theory is free of ghosts and renormalizable when we analyze fluctuations on the flat background.Physical review D: Particles and fields 08/2012; 87(6).  Physics Letters B. 07/2012; 713(s 4–5):514.
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ABSTRACT: The thermal correction to the energy of CasimirPolder interaction of atoms with a suspended graphene membrane described by the Dirac model is investigated. We show that a major impact on the thermal correction is made by the size of the gap in the energy spectrum of graphene quasiparticles. Specifically, if the temperature is much smaller than the gap parameter (alternatively, larger or of the order of the gap parameter), the thermal correction is shown to be relatively small (alternatively, large). We have calculated the free energy of the thermal CasimirPolder interaction of atoms of He, Na, Rb, and Cs with graphene described by both the hydrodynamic and Dirac models. It is shown that in exact computations using the Dirac model, one should use the polarization operator at nonzero temperature. The computational results for the CasimirPolder free energy obtained in the framework of hydrodynamic model of graphene are several times larger than in the Dirac model within the separation region below 2$\mu$m. We conclude that the theoretical predictions following from the two models can be reliably discriminated in experiments on quantum reflection of different atoms on graphene.Physical Review A 07/2012; 86(1). · 3.04 Impact Factor 
Article: Erratum to
Physics Letters B 07/2012; 713(4):514514. · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present several theories of fourdimensional gravity in the Plebanski formulation, in which the tetrads and the connections are the independent dynamical variables. We consider the relation between different versions of gravitational theories: Einstenian, dual, 'mirror' gravities and gravity with torsion. According to Plebanski's assumption, our world, in which we live, is described by the selfdual lefthanded gravity. We propose that if the Mirror World exists in Nature, then the 'mirror gravity' is the righthanded antiselfdual gravity with broken mirror parity. Considering a special version of the RiemannCartan spacetime, which has torsion as additional geometric property, we have shown that in the Plebanski formulation the ordinary and dual sectors of gravity, as well as the gravity with torsion, are equivalent. In this context, we have also developed a 'pure connection gravity'  a diffeomorphisminvariant gauge theory of gravity. We have calculated the partition function and the effective Lagrangian of this fourdimensional gravity and have investigated the limit of this theory at small distances.International Journal of Modern Physics A 06/2012; 28(12). · 1.13 Impact Factor 
Article: Lorentzinvariant CPT violation
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ABSTRACT: A Lorentzinvariant CPT violation, which may be termed as longdistance CPT violation in contrast to the familiar shortdistance CPT violation, has been recently proposed. This scheme is based on a nonlocal interaction vertex and characterized by an infrared divergent form factor. We show that the Lorentz covariant $T^{\star}$product is consistently defined and the energymomentum conservation is preserved in perturbation theory if the path integral is suitably defined for this nonlocal theory, although unitarity is generally lost. It is illustrated that T violation is realized in the decay and formation processes. It is also argued that the equality of masses and decay widths of the particle and antiparticle is preserved if the nonlocal CPT violation is incorporated either directly or as perturbation by starting with the conventional CPTeven local Lagrangian. However, we also explicitly show that the present nonlocal scheme can induce the splitting of particle and antiparticle mass eigenvalues if one considers a more general class of Lagrangians.European Physical Journal C 05/2012; 73(3). · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We classify the unitary representations of the extended Poincar\'e supergroups in three dimensions. Irreducible unitary representations of any spin can appear, which correspond to supersymmetric anyons. Our results also show that all irreducible unitary representations necessarily have physical momenta. This is in sharp contrast to the ordinary Poincar\'e group in three dimensions, that admits in addition irreducible unitary representations with nonphysical momenta, which are discarded on physical grounds.Journal of Mathematical Physics 04/2012; 53(7). · 1.30 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The interpretation of neutrino oscillation data has led to the question whether, in principle, an antiparticle like antineutrino can have a different mass than its particle. In the framework of a Lorentz invariant CPT violation, which is based on the nonlocal interaction vertex and characterized by the infrared divergent form factor, we present an explicit Lagrangian model for the fermion and antifermion mass splitting.Physics Letters B 03/2012; 712(s 1–2). · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The full text of this article is available in the PDF provided.Classical and Quantum Gravity 01/2012; 29(15). · 3.56 Impact Factor
Publication Stats
2k  Citations  
261.37  Total Impact Points  
Top Journals
Institutions

2000–2013

University of Helsinki
 • Department of Physics
 • Department of Physical Sciences
Helsinki, Southern Finland Province, Finland


2009

Institute for Research in Fundamental Sciences (IPM)
 Physics
Tehrān, Ostane Tehran, Iran 
University of São Paulo
 Instituto de Física (IF) (São Paulo)
Ribeirão Preto, Estado de Sao Paulo, Brazil


2006

University of North Carolina at Chapel Hill
North Carolina, United States 
The University of Tokyo
 Department of Physics
Tokyo, Tokyoto, Japan 
Andronikashvili Institute of Physics
Tbilsi, T'bilisi, Georgia


2001

Helsinki Institute of Physics (HIP)
Esbo, Southern Finland Province, Finland
