Real scalar field • minimally coupled, canonical [Hoenselaers 1978; I.Sm. 2015] X ≡ − 1 2 ( ∇ c φ )( ∇ T ab = ( ∇ a φ )( ∇ b φ ) + ( X − V ( φ )) g ab , c φ ) 0 = £ ξ V ( φ ) = V ′ ( φ ) £ ξ φ ⇒ V ′ ( φ ) � = 0 £ ξ φ = 0 V ′ ( φ ) = 0 £ ξ φ = a = const . and if ξ a has compact orbits then a = 0.

• an example of time dependent real scalar field in a stationary spacetime: M. Wyman, Phys. Rev. D 24 (1981) 839 d s 2 = − e ν ( r ) d t 2 + e λ ( r ) d r 2 + r 2 ( d θ 2 + sin 2 θ d ϕ 2 ) φ ( t ) = γ t , γ = const .

• an example of time dependent real scalar field in a stationary spacetime: M. Wyman, Phys. Rev. D 24 (1981) 839 d s 2 = − e ν ( r ) d t 2 + e λ ( r ) d r 2 + r 2 ( d θ 2 + sin 2 θ d ϕ 2 ) φ ( t ) = γ t , γ = const . two solutions: a simpler one with e ν = 8 πγ 2 r 2 and e λ = 2, and • the second one in a form a Taylor series.

• “k-essence” theories a generic model for the inflationary evolution T ab = p , X ( ∇ a φ )( ∇ b φ ) + p g ab , p = p ( φ, X )

• “k-essence” theories a generic model for the inflationary evolution T ab = p , X ( ∇ a φ )( ∇ b φ ) + p g ab , p = p ( φ, X ) • lemma [I.Sm. 2015] £ ξ p = £ ξ ( Xp , X ) = 0

• “k-essence” theories a generic model for the inflationary evolution T ab = p , X ( ∇ a φ )( ∇ b φ ) + p g ab , p = p ( φ, X ) • lemma [I.Sm. 2015] £ ξ p = £ ξ ( Xp , X ) = 0 Xp , X = 0 ⇒ £ ξ £ ξ φ = 0 along the orbit (for admissible T ab )

• “k-essence” theories a generic model for the inflationary evolution T ab = p , X ( ∇ a φ )( ∇ b φ ) + p g ab , p = p ( φ, X ) • lemma [I.Sm. 2015] £ ξ p = £ ξ ( Xp , X ) = 0 Xp , X = 0 ⇒ £ ξ £ ξ φ = 0 along the orbit (for admissible T ab ) Xp , X � = 0 ⇒ £ ξ φ is a solution to p ,φ ( £ ξ φ ) 2 + 2 Xp , X £ ξ £ ξ φ = 0 which is either identically zero or doesn’t have any zeros along the orbit of ξ a

Addendum: Ideal fluid

Addendum: Ideal fluid • [Hoenselaers 1978] T ab = ( ρ + p ) u a u b + p g ab

Addendum: Ideal fluid • [Hoenselaers 1978] T ab = ( ρ + p ) u a u b + p g ab £ ξ T ab = 0 ⇒ £ ξ ρ = £ ξ p = 0 = £ ξ u a

Complex scalar field

Complex scalar field • energy-momentum tensor b ) φ ∗ − 1 c φ ∗ + V ( φ ∗ φ ) ∇ c φ ∇ � � T ab = ∇ ( a φ ∇ g ab 2

Complex scalar field • energy-momentum tensor b ) φ ∗ − 1 c φ ∗ + V ( φ ∗ φ ) ∇ c φ ∇ � � T ab = ∇ ( a φ ∇ g ab 2 e.g. in polar form φ = Ae i α : • b α + T + V ( A 2 ) b A + A 2 ∇ T ab = ∇ a A ∇ a α ∇ g ab D − 2

• subcase #1: symmetry inheriting amplitude, £ ξ A = 0 → £ ξ α is a constant !

• subcase #1: symmetry inheriting amplitude, £ ξ A = 0 → £ ξ α is a constant ! • subcase #2: symmetry inheriting phase, £ ξ α = 0, N ( £ ξ A ) 2 + D − 2 V ( A 2 ) = λ

• subcase #1: symmetry inheriting amplitude, £ ξ A = 0 → £ ξ α is a constant ! • subcase #2: symmetry inheriting phase, £ ξ α = 0, N ( £ ξ A ) 2 + D − 2 V ( A 2 ) = λ ⋆ for V = µ 2 A 2 , the only symmetry noninheriting amplitude A which is bounded or periodic along the orbits of ξ a is A ∼ sin ( √ κ ( x − x 0 )) but N = const . > 0 and ξ a is hypersurface orthogonal

Black Hole Hair

What is black hole hair?

What is black hole hair? • the term was coined by J.A. Wheeler and R. Ruffini, Introducing the black hole , Physics Today 24 (1971) 30

What is black hole hair? • the term was coined by J.A. Wheeler and R. Ruffini, Introducing the black hole , Physics Today 24 (1971) 30 • roughly, a broad definition: any non-gravitational field in a black hole spacetime

What is black hole hair? • the term was coined by J.A. Wheeler and R. Ruffini, Introducing the black hole , Physics Today 24 (1971) 30 • roughly, a broad definition: any non-gravitational field in a black hole spacetime • more refined definition: any non-gravitational field in a black hole spacetime contributing to the conserved “charges” associated to the black hole, apart from the total mass M , the angular momentum J , the electric charge Q and the magnetic charge P (see also: primary/secondary hair distinction)

No-hair theorems

No-hair theorems • Bekenstein, PRL 28 (1971) 452

No-hair theorems • Bekenstein, PRL 28 (1971) 452 The absence of the scalar black hole hair is always proven under some particular assumptions about the scalar field φ ,

No-hair theorems • Bekenstein, PRL 28 (1971) 452 The absence of the scalar black hole hair is always proven under some particular assumptions about the scalar field φ , (a) a choice of the scalar field coupling to gravity,

No-hair theorems • Bekenstein, PRL 28 (1971) 452 The absence of the scalar black hole hair is always proven under some particular assumptions about the scalar field φ , (a) a choice of the scalar field coupling to gravity, (b) an energy condition ,

No-hair theorems • Bekenstein, PRL 28 (1971) 452 The absence of the scalar black hole hair is always proven under some particular assumptions about the scalar field φ , (a) a choice of the scalar field coupling to gravity, (b) an energy condition , (c) details about the “asymptotics”

No-hair theorems • Bekenstein, PRL 28 (1971) 452 The absence of the scalar black hole hair is always proven under some particular assumptions about the scalar field φ , (a) a choice of the scalar field coupling to gravity, (b) an energy condition , (c) details about the “asymptotics” (d) the assumption that the scalar field φ inherits the spacetime symmetries

Symmetry noninheriting scalar black hole hair

Symmetry noninheriting scalar black hole hair • Herdeiro and Radu, PRL 112 (2014) 221101

Symmetry noninheriting scalar black hole hair • Herdeiro and Radu, PRL 112 (2014) 221101 numerical stationary axially symmetric solution of the Einstein-Klein-Gordon EOM, with the complex scalar field φ = A ( r , θ ) e i ( m ϕ − ω t ) with ω = Ω H m

Symmetry noninheriting scalar black hole hair • Herdeiro and Radu, PRL 112 (2014) 221101 numerical stationary axially symmetric solution of the Einstein-Klein-Gordon EOM, with the complex scalar field φ = A ( r , θ ) e i ( m ϕ − ω t ) with ω = Ω H m • Are there any other hairy black hole solutions based on symmetry noninheritance? What are the constraints on the existence of the sni scalar black hole hair?

• on any Killing horizon H [ ξ ] we have R ( ξ, ξ ) = 0

• on any Killing horizon H [ ξ ] we have R ( ξ, ξ ) = 0 • thus, for the Einstein-KG, T ( ξ, ξ ) = 0 on H [ ξ ]

• on any Killing horizon H [ ξ ] we have R ( ξ, ξ ) = 0 • thus, for the Einstein-KG, T ( ξ, ξ ) = 0 on H [ ξ ] → implications [I.Sm. 2015]

• on any Killing horizon H [ ξ ] we have R ( ξ, ξ ) = 0 • thus, for the Einstein-KG, T ( ξ, ξ ) = 0 on H [ ξ ] → implications [I.Sm. 2015] ⋆ real canonical scalar field, £ ξ φ = 0 (no sni BH hair!)

• on any Killing horizon H [ ξ ] we have R ( ξ, ξ ) = 0 • thus, for the Einstein-KG, T ( ξ, ξ ) = 0 on H [ ξ ] → implications [I.Sm. 2015] ⋆ real canonical scalar field, £ ξ φ = 0 (no sni BH hair!) ⋆ complex scalar field with symmetry inheriting amplitude: a constraint for H [ χ ] with χ a = k a + Ω H m a £ k α + Ω H £ m α = 0

• on any Killing horizon H [ ξ ] we have R ( ξ, ξ ) = 0 • thus, for the Einstein-KG, T ( ξ, ξ ) = 0 on H [ ξ ] → implications [I.Sm. 2015] ⋆ real canonical scalar field, £ ξ φ = 0 (no sni BH hair!) ⋆ complex scalar field with symmetry inheriting amplitude: a constraint for H [ χ ] with χ a = k a + Ω H m a £ k α + Ω H £ m α = 0 ⋆ complex scalar field with symmetry inheriting phase: no sni BH hair (via Vishveshwara-Carter tm)

Hair constraints beyond Einstein [I.Sm. arXiv:1609.04013]

Hair constraints beyond Einstein [I.Sm. arXiv:1609.04013] • idea: use the Frobenius’ theorem (diff. geom.)

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