Hypothetical particle found in supergravity
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Intheoretical physics , thedual graviton is a hypotheticalelementary particle that is a dual of thegraviton underelectric-magnetic duality , as anS-duality , predicted by some formulations ofeleven-dimensional supergravity .[ 3]
The dual graviton was firsthypothesized in 1980.[ 4] It was theoretically modeled in 2000s,[ 1] [ 2] which was then predicted in eleven-dimensional mathematics of SO(8)supergravity in the framework of electric-magnetic duality.[ 3] It again emerged in theE 11 generalized geometry in eleven dimensions,[ 5] and theE 7 generalized vielbein-geometry in eleven dimensions.[ 6] While there is no local coupling between graviton and dual graviton, the field introduced by dual graviton may be coupled to aBF model as non-local gravitational fields in extra dimensions.[ 7]
Amassive dual gravity of Ogievetsky–Polubarinov model[ 8] can be obtained by coupling the dual graviton field to the curl of its own energy-momentum tensor.[ 9] [ 10]
The previously mentioned theories of dual graviton are in flat space. Inde Sitter andanti-de Sitter spaces (A)dS, the massless dual graviton exhibits less gauge symmetries dynamics compared with those ofCurtright field in flat space, hence the mixed-symmetry field propagates in more degrees of freedom.[ 11] However, the dual graviton in (A)dS transforms under GL(D) representation, which is identical to that of massive dual graviton in flat space.[ 12] This apparent paradox can be resolved using the unfolding technique in Brink, Metsaev, and Vasiliev conjecture.[ 13] [ 14] For the massive dual graviton in (A)dS, the flat limit is clarified after expressing dual field in terms of theStueckelberg coupling of a massless spin-2 field with aProca field.[ 11]
Dual linearized gravity [ edit ] The dual formulations of linearized gravity are described by a mixed Young symmetry tensorT λ 1 λ 2 ⋯ λ D − 3 μ {\displaystyle T_{\lambda _{1}\lambda _{2}\cdots \lambda _{D-3}\mu }} , the so-called dual graviton, in any spacetime dimensionD > 4 with the following characters:[ 2] [ 15]
T λ 1 λ 2 ⋯ λ D − 3 μ = T [ λ 1 λ 2 ⋯ λ D − 3 ] μ , {\displaystyle T_{\lambda _{1}\lambda _{2}\cdots \lambda _{D-3}\mu }=T_{[\lambda _{1}\lambda _{2}\cdots \lambda _{D-3}]\mu },} T [ λ 1 λ 2 ⋯ λ D − 3 μ ] = 0. {\displaystyle T_{[\lambda _{1}\lambda _{2}\cdots \lambda _{D-3}\mu ]}=0.} where square brackets show antisymmetrization.
For 5-D spacetime, the spin-2 dual graviton is described by theCurtright field T α β γ {\displaystyle T_{\alpha \beta \gamma }} . The symmetry properties imply that
T α β γ = T [ α β ] γ , {\displaystyle T_{\alpha \beta \gamma }=T_{[\alpha \beta ]\gamma },} T [ α β ] γ + T [ β γ ] α + T [ γ α ] β = 0. {\displaystyle T_{[\alpha \beta ]\gamma }+T_{[\beta \gamma ]\alpha }+T_{[\gamma \alpha ]\beta }=0.} The Lagrangian action for the spin-2 dual gravitonT λ 1 λ 2 μ {\displaystyle T_{\lambda _{1}\lambda _{2}\mu }} in 5-D spacetime, theCurtright field , becomes[ 2] [ 15]
L d u a l = − 1 12 ( F [ α β γ ] δ F [ α β γ ] δ − 3 F [ α β ξ ] ξ F [ α β λ ] λ ) , {\displaystyle {\cal {L}}_{\rm {dual}}=-{\frac {1}{12}}\left(F_{[\alpha \beta \gamma ]\delta }F^{[\alpha \beta \gamma ]\delta }-3F_{[\alpha \beta \xi ]}{}^{\xi }F^{[\alpha \beta \lambda ]}{}_{\lambda }\right),} whereF α β γ δ {\displaystyle F_{\alpha \beta \gamma \delta }} is defined as
F [ α β γ ] δ = ∂ α T [ β γ ] δ + ∂ β T [ γ α ] δ + ∂ γ T [ α β ] δ , {\displaystyle F_{[\alpha \beta \gamma ]\delta }=\partial _{\alpha }T_{[\beta \gamma ]\delta }+\partial _{\beta }T_{[\gamma \alpha ]\delta }+\partial _{\gamma }T_{[\alpha \beta ]\delta },} and the gauge symmetry of theCurtright field is
δ σ , α T [ α β ] γ = 2 ( ∂ [ α σ β ] γ + ∂ [ α α β ] γ − ∂ γ α α β ) . {\displaystyle \delta _{\sigma ,\alpha }T_{[\alpha \beta ]\gamma }=2(\partial _{[\alpha }\sigma _{\beta ]\gamma }+\partial _{[\alpha }\alpha _{\beta ]\gamma }-\partial _{\gamma }\alpha _{\alpha \beta }).} The dualRiemann curvature tensor of the dual graviton is defined as follows:[ 2]
E [ α β δ ] [ ε γ ] ≡ 1 2 ( ∂ ε F [ α β δ ] γ − ∂ γ F [ α β δ ] ε ) , {\displaystyle E_{[\alpha \beta \delta ][\varepsilon \gamma ]}\equiv {\frac {1}{2}}(\partial _{\varepsilon }F_{[\alpha \beta \delta ]\gamma }-\partial _{\gamma }F_{[\alpha \beta \delta ]\varepsilon }),} and the dualRicci curvature tensor andscalar curvature of the dual graviton become, respectively
E [ α β ] γ = g ε δ E [ α β δ ] [ ε γ ] , {\displaystyle E_{[\alpha \beta ]\gamma }=g^{\varepsilon \delta }E_{[\alpha \beta \delta ][\varepsilon \gamma ]},} E α = g β γ E [ α β ] γ . {\displaystyle E_{\alpha }=g^{\beta \gamma }E_{[\alpha \beta ]\gamma }.} They fulfill the following Bianchi identities
∂ α ( E [ α β ] γ + g γ [ α E β ] ) = 0 , {\displaystyle \partial _{\alpha }(E^{[\alpha \beta ]\gamma }+g^{\gamma [\alpha }E^{\beta ]})=0,} whereg α β {\displaystyle g^{\alpha \beta }} is the 5-D spacetime metric.
Massive dual gravity [ edit ] In 4-D, the Lagrangian of thespinless massive version of the dual gravity is
L d u a l , m a s s i v e s p i n l e s s = − 1 2 u + 1 2 ( v − g u ) 2 + 1 3 g ( v − g u ) 3 F 3 F 2 ( 1 , 1 2 , 3 2 ; 2 , 5 2 ; − 4 g 2 ( v − g u ) 2 ) , {\displaystyle {\mathcal {L_{\rm {dual,massive}}^{\rm {spinless}}}}=-{\frac {1}{2}}u+{\frac {1}{2}}(v-gu)^{2}+{\frac {1}{3}}g(v-gu)^{3}\sideset {_{3}}{_{2}}F(1,{\frac {1}{2}},{\frac {3}{2}};2,{\frac {5}{2}};-4g^{2}(v-gu)^{2}),}
whereV μ = 1 6 ϵ μ α β γ V α β γ , v = V μ V μ and u = ∂ μ V μ . {\displaystyle V^{\mu }={\frac {1}{6}}\epsilon ^{\mu \alpha \beta \gamma }V_{\alpha \beta \gamma }~,v=V_{\mu }V^{\mu }{\text{and}}~u=\partial _{\mu }V^{\mu }.} [ 16] The coupling constantg / m {\displaystyle g/m} appears in the equation of motion to couple the trace of the conformally improved energy momentum tensorθ {\displaystyle \theta } to the field as in the following equation
( ◻ + m 2 ) V μ = g m ∂ μ θ . {\displaystyle \left(\Box +m^{2}\right)V_{\mu }={\frac {g}{m}}\partial _{\mu }\theta .}
And for the spin-2 massive dual gravity in 4-D,[ 10] the Lagrangian is formulated in terms of theHessian matrix that also constitutesHorndeski theory (Galileons/massive gravity ) through
det ( δ ν μ + g m K ν μ ) = 1 − 1 2 ( g / m ) 2 K α β K β α + 1 3 ( g / m ) 3 K α β K β γ K γ α + 1 8 ( g / m ) 4 [ ( K α β K β α ) 2 − 2 K α β K β γ K γ δ K δ α ] , {\displaystyle {\text{det}}(\delta _{\nu }^{\mu }+{\frac {g}{m}}K_{\nu }^{\mu })=1-{\frac {1}{2}}(g/m)^{2}K_{\alpha }^{\beta }K_{\beta }^{\alpha }+{\frac {1}{3}}(g/m)^{3}K_{\alpha }^{\beta }K_{\beta }^{\gamma }K_{\gamma }^{\alpha }+{\frac {1}{8}}(g/m)^{4}\left[(K_{\alpha }^{\beta }K_{\beta }^{\alpha })^{2}-2K_{\alpha }^{\beta }K_{\beta }^{\gamma }K_{\gamma }^{\delta }K_{\delta }^{\alpha }\right],}
whereK μ ν = 3 ∂ α T [ β γ ] μ ϵ α β γ ν {\displaystyle K_{\mu }^{\nu }=3\partial _{\alpha }T_{[\beta \gamma ]\mu }\epsilon ^{\alpha \beta \gamma \nu }} .
So the zeroth interaction part, i.e., the third term in the Lagrangian, can be read asK α β θ β α {\displaystyle K_{\alpha }^{\beta }\theta _{\beta }^{\alpha }} so the equation of motion becomes
( ◻ + m 2 ) T [ α β ] γ = g m P α β γ , λ μ ν ∂ λ θ μ ν , {\displaystyle \left(\Box +m^{2}\right)T_{[\alpha \beta ]\gamma }={\frac {g}{m}}P_{\alpha \beta \gamma ,\lambda \mu \nu }\partial ^{\lambda }\theta ^{\mu \nu },}
where theP α β γ , λ μ ν = 2 ϵ α β λ μ η γ ν + ϵ α γ λ μ η β ν − ϵ β γ λ μ η α ν {\displaystyle P_{\alpha \beta \gamma ,\lambda \mu \nu }=2\epsilon _{\alpha \beta \lambda \mu }\eta _{\gamma \nu }+\epsilon _{\alpha \gamma \lambda \mu }\eta _{\beta \nu }-\epsilon _{\beta \gamma \lambda \mu }\eta _{\alpha \nu }} isYoung symmetrizer of such SO(2) theory.
For solutions of the massive theory in arbitrary N-D, i.e., Curtright fieldT [ λ 1 λ 2 . . . λ N − 3 ] μ {\displaystyle T_{[\lambda _{1}\lambda _{2}...\lambda _{N-3}]\mu }} , the symmetrizer becomes that of SO(N-2).[ 9]
Dual graviton coupling with BF theory [ edit ] Dual gravitons have interaction with topologicalBF model inD = 5 through the following Lagrangian action[ 7]
S L = ∫ d 5 x ( L d u a l + L B F ) . {\displaystyle S_{\rm {L}}=\int d^{5}x({\cal {L}}_{\rm {dual}}+{\cal {L}}_{\rm {BF}}).} where
L B F = T r [ B ∧ F ] {\displaystyle {\cal {L}}_{\rm {BF}}=Tr[\mathbf {B} \wedge \mathbf {F} ]} Here,F ≡ d A ∼ R a b {\displaystyle \mathbf {F} \equiv d\mathbf {A} \sim R_{ab}} is thecurvature form , andB ≡ e a ∧ e b {\displaystyle \mathbf {B} \equiv e^{a}\wedge e^{b}} is the background field.
In principle, it should similarly be coupled to a BF model of gravity as the linearized Einstein–Hilbert action inD > 4:
S B F = ∫ d 5 x L B F ∼ S E H = 1 2 ∫ d 5 x R − g . {\displaystyle S_{\rm {BF}}=\int d^{5}x{\cal {L}}_{\rm {BF}}\sim S_{\rm {EH}}={1 \over 2}\int \mathrm {d} ^{5}xR{\sqrt {-g}}.} whereg = det ( g μ ν ) {\displaystyle g=\det(g_{\mu \nu })} is the determinant of themetric tensor matrix, andR {\displaystyle R} is theRicci scalar .
Dual gravitoelectromagnetism [ edit ] In similar manner while we definegravitoelectromagnetism for the graviton, we can define electric and magnetic fields for the dual graviton.[ 17] There are the following relation between the gravitoelectric fieldE a b [ h a b ] {\displaystyle E_{ab}[h_{ab}]} and gravitomagnetic fieldB a b [ h a b ] {\displaystyle B_{ab}[h_{ab}]} of the gravitonh a b {\displaystyle h_{ab}} and the gravitoelectric fieldE a b [ T a b c ] {\displaystyle E_{ab}[T_{abc}]} and gravitomagnetic fieldB a b [ T a b c ] {\displaystyle B_{ab}[T_{abc}]} of the dual gravitonT a b c {\displaystyle T_{abc}} :[ 18] [ 15]
B a b [ T a b c ] = E a b [ h a b ] {\displaystyle B_{ab}[T_{abc}]=E_{ab}[h_{ab}]} E a b [ T a b c ] = − B a b [ h a b ] {\displaystyle E_{ab}[T_{abc}]=-B_{ab}[h_{ab}]} andscalar curvature R {\displaystyle R} with dual scalar curvatureE {\displaystyle E} :[ 18]
E = ⋆ R {\displaystyle E=\star R} R = − ⋆ E {\displaystyle R=-\star E} where⋆ {\displaystyle \star } denotes theHodge dual .
Dual graviton in conformal gravity [ edit ] The free (4,0)conformal gravity inD = 6 is defined as
S = ∫ d 6 x − g C A B C D C A B C D , {\displaystyle {\mathcal {S}}=\int \mathrm {d} ^{6}x{\sqrt {-g}}C_{ABCD}C^{ABCD},} whereC A B C D {\displaystyle C_{ABCD}} is theWeyl tensor inD = 6. The free (4,0) conformal gravity can be reduced to the graviton in the ordinary space, and the dual graviton in the dual space inD = 4.[ 19]
It is easy to notice the similarity between theLanczos tensor , that generates the Weyl tensor in geometric theories of gravity, and Curtright tensor, particularly their shared symmetry properties of the linearized spin connection in Einstein's theory. However, Lanczos tensor is a tensor of geometry in D=4,[ 20] meanwhile Curtright tensor is a field tensor in arbitrary dimensions.
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