Critical magnetic fields for the magnetic Dirac-Coulomb operator. Maria J. ESTEBAN. C.N.R.S. and University Paris-Dauphine

Critical magnetic fields for the magnetic Dirac-Coulomb operator Maria J. ESTEBAN C.N.R.S. and University Paris-Dauphine In collaboration with : Jean Dolbeault and Michael Loss http://www.ceremade.dauphine.fr/ e esteban/ John60, Edinburgh, June 2008 p.1/20

Physical problem Very strong magnetic fields could : destabilize matter, distorting atoms and molecules and forming polymer-like chains, facilitate the massive spontaneous appearance of positron-electron pairs, the best candidate for this to happen are the magnetars (neutron stars), in which huge gravitational collapses would facilitate the appearance of huge magnetic fields, magnetars appear today as the most possible hypothesis for the so called gamma ray outbursts" Earth s magnetic field = 1 Gauss Maximal field on Earth (MRI) = 1 Tesla = 10 4 Gauss Deatly field strength = 10 5 Tesla = 10 9 Gauss In new magnetars one expectes fields of 10 11 Tesla. In recent theories, up to 10 16 Tesla in the heart of the magnetars. John60, Edinburgh, June 2008 p.2/20

How to find models sustaining those huge magnetic fields? relativistic electronic models (Dirac) with homogeneous magnetic fields and abnomal magnetic moments (V. Canuto, H.-Y. Chiu; R.F. O Connell), hydrogenic atoms in a curved universe (Nowotny), intense electrostatic fields... (..., Brodsky, Mohr,...), heterogeneous magnetic fields (P. Achuthan et al), Excellent presentation in the works of R.C. Duncan and C. Thompson. Electrons submitted to an external electromagnetic field with homogeneous magnetic field. John60, Edinburgh, June 2008 p.3/20

The free Dirac operator H = i α + β, α 1, α 2, α 3, β M 4 4 (CI) (c = m = = 1) John60, Edinburgh, June 2008 p.4/20

The free Dirac operator H = i α + β, α 1, α 2, α 3, β M 4 4 (CI) (c = m = = 1)! β = I 0 0 I, α k = 0 σ k σ k 0! (k = 1,2,3) John60, Edinburgh, June 2008 p.4/20

The free Dirac operator H = i α + β, α 1, α 2, α 3, β M 4 4 (CI) (c = m = = 1)! β = I 0 0 I, α k = 0 σ k σ k 0! (k = 1,2,3)! σ 1 = 0 1 1 0!, σ 2 = 0 i i 0!, σ 3 = 1 0 0 1 John60, Edinburgh, June 2008 p.4/20

The free Dirac operator H = i α + β, α 1, α 2, α 3, β M 4 4 (CI) (c = m = = 1)! β = I 0 0 I, α k = 0 σ k σ k 0! (k = 1,2,3)! σ 1 = 0 1 1 0!, σ 2 = 0 i i 0!, σ 3 = 1 0 0 1 The two main properties of H are: H 2 = + I 1, σ(h) = (, 1] [1,+ ) John60, Edinburgh, June 2008 p.4/20

Eigenvalues of the Dirac operator without magnetic field Let us first consider the case of Coulomb potentials V ν := ν x, ν > 0. John60, Edinburgh, June 2008 p.5/20

Eigenvalues of the Dirac operator without magnetic field Let us first consider the case of Coulomb potentials V ν := ν x, ν > 0. H ν := H 0 ν x can be defined as a self-adjoint operator if 0 < ν < 1 (actually also (recent result) if ν = 1). Its spectrum is given by: σ(h ν ) = (, 1] {λ ν 1, λ ν 2,... } [1, ) 0 < λ ν 1 = p 1 ν 2 λ ν k < 1. and the fact that λ 1 (H + V ν ) belongs to ( 1,1) is a kind of stability condition" for the electron. John60, Edinburgh, June 2008 p.5/20

Magnetic case I When a external magnetic field B is present, one considers a magnetic potential A B s. t. curla B = B. John60, Edinburgh, June 2008 p.6/20

Magnetic case I When a external magnetic field B is present, one considers a magnetic potential A B s. t. curla B = B. One has then to replace with B = ia B John60, Edinburgh, June 2008 p.6/20

Magnetic case I When a external magnetic field B is present, one considers a magnetic potential A B s. t. curla B = B. One has then to replace with B = ia B H B = i α B + β John60, Edinburgh, June 2008 p.6/20

Magnetic case I When a external magnetic field B is present, one considers a magnetic potential A B s. t. curla B = B. One has then to replace with B = ia B H B = i α B + β If we consider H B + V, if this operator is self-adjoint, if its essential spectrum is the set (, 1] [1,+ ) plus a discrete number of eigenvalues in the spectral gap ( 1, 1), John60, Edinburgh, June 2008 p.6/20

Eigenvalues below / in the middle of the continuous spectrum. Spectrum of a self-adjoint operator A : John60, Edinburgh, June 2008 p.7/20

Eigenvalues below / in the middle of the continuous spectrum. Spectrum of a self-adjoint operator A : In the first case, λ 1 = min x 0 (Ax, x) x 2 John60, Edinburgh, June 2008 p.7/20

Eigenvalues below / in the middle of the continuous spectrum. Spectrum of a self-adjoint operator A : In the first case, λ 1 = min x 0 (Ax, x) x 2 In the second case, λ 1 = min max?? (Ax, x) x 2, λ 1 = max? min? (Ax, x) x 2,... John60, Edinburgh, June 2008 p.7/20

Abstract min-max theorem (Dolbeault, E., Séré, 2000) Let H be a Hilbert space and A : F = D(A) H H a self-adjoint operator defined on H. Let H +, H be two orthogonal subspaces of H satisfying: H = H + H. Define F ± := P ± F. (i) a := sup x F \{0} (x, Ax ) x 2 H < +. Let c k = inf V subspace of F + dim V =k sup x (V F )\{0} (x, Ax) x 2 H, k 1. John60, Edinburgh, June 2008 p.8/20

Application to magnetic Dirac operators I ψ : IR 3 C 4, ψ = «ϕ χ = ϕ 0 + «0 χ, ϕ, χ : IR 3 CI 2 John60, Edinburgh, June 2008 p.9/20

Application to magnetic Dirac operators I ψ : IR 3 C 4, ψ = «ϕ χ = ϕ 0 + «0 χ, ϕ, χ : IR 3 CI 2 Suppose that V satisfies lim V (x) = 0, x + ν x V 0, John60, Edinburgh, June 2008 p.9/20

Application to magnetic Dirac operators I «ϕ ϕ «0 ψ : IR 3 C 4, ψ = = + χ 0 χ, ϕ, χ : IR 3 CI 2 Suppose that V satisfies lim V (x) = 0, x + ν x V 0, Then, for all k 1, λ k (B, V ) = inf Y subspace of C o (IR3,CI 2 ) dimy =k sup ϕ Y \{0} sup ψ= ϕ χ χ C 0 (IR3,C 2 ) (ψ,(h B + V )ψ) (ψ, ψ) John60, Edinburgh, June 2008 p.9/20

Application to magnetic Dirac operators II The first eigenvalue of H B + V in the spectral hole ( 1,1) is given by λ 1 (B, V ) := inf sup ϕ 0 χ (ψ, (H B + V )ψ) (ψ, ψ), ψ = «ϕ χ John60, Edinburgh, June 2008 p.10/20

Application to magnetic Dirac operators II The first eigenvalue of H B + V in the spectral hole ( 1,1) is given by λ 1 (B, V ) := inf sup ϕ 0 χ (ψ, (H B + V )ψ) (ψ, ψ), ψ = «ϕ χ and λ B (ϕ) := sup ψ= ϕ χ (ψ, (H B + V )ψ) (ψ, ψ) χ C 0 (IR3,C 2 ) John60, Edinburgh, June 2008 p.10/20

Application to magnetic Dirac operators III λ 1 (B, V ) = inf ϕ C 0 (IR3,C 2 ) ϕ 0 λ B (ϕ) John60, Edinburgh, June 2008 p.11/20

Application to magnetic Dirac operators III λ 1 (B, V ) = inf ϕ C 0 (IR3,C 2 ) ϕ 0 λ B (ϕ) σ B ϕ 2 IR 3 1 V + λ B (ϕ) + (V + 1 λb (ϕ)) ϕ 2 dx = 0 John60, Edinburgh, June 2008 p.11/20

Application to magnetic Dirac operators III λ 1 (B, V ) = inf ϕ C 0 (IR3,C 2 ) ϕ 0 λ B (ϕ) σ B ϕ 2 IR 3 1 V + λ B (ϕ) + (V + 1 λb (ϕ)) ϕ 2 dx = 0 IR3 (σ B )ϕ 2 1 + λ 1 (B, V ν ) + ν x dx + (1 λ 1 (B, V ν )) ϕ 2 dx IR 3 IR 3 ν x ϕ 2 dx John60, Edinburgh, June 2008 p.11/20

For a potential V = V ν, ν (0,1), 0 < B1 < B2 < B(ν) : B=0-1 1 B=B1 B=B2 B=B(ν) -1 1 John60, Edinburgh, June 2008 p.12/20

For a potential V = V ν, ν (0,1), 0 < B1 < B2 < B(ν) : B=0-1 1 B=B1 B=B2 B=B(ν) -1 1 DEFINITION: B(ν) := inf B > 0 : liminf bրb λ 1 (B, ν) = 1. John60, Edinburgh, June 2008 p.12/20

For a potential V = V ν, ν (0,1), 0 < B1 < B2 < B(ν) : B=0-1 1 B=B1 B=B2 B=B(ν) -1 1 DEFINITION: B(ν) := inf B > 0 : liminf bրb λ 1 (B, ν) = 1. TOOL TO ESTIMATE IT : IR3 (σ B )ϕ 2 1 + λ 1 (B, V ) V dx + (1 λ 1(B, V )) ϕ 2 dx IR 3 IR 3 V ϕ 2 dx John60, Edinburgh, June 2008 p.12/20

First results to estimate λ 1 (B,V ) For a given C, we have λ 1 (B, V ) < C if we can find a function ϕ s. t. ( ) IR3 (σ B ) ϕ 2 1 + C V dx + (1 C) ϕ 2 dx + IR 3 V ϕ 2 dx < 0 IR 3 John60, Edinburgh, June 2008 p.13/20

First results to estimate λ 1 (B,V ) For a given C, we have λ 1 (B, V ) < C if we can find a function ϕ s. t. ( ) IR3 (σ B ) ϕ 2 1 + C V dx + (1 C) ϕ 2 dx + IR 3 V ϕ 2 dx < 0 IR 3 And to verify that λ 1 (B, V ) > C it is enough to prove that for all ϕ ( ) IR3 (σ B )ϕ 2 1 + C V dx + (1 C) ϕ 2 dx + V ϕ 2 dx > 0 IR 3 IR 3 John60, Edinburgh, June 2008 p.13/20

Some results (with J. Dolbeault and M. Loss) V ν = ν x, A B(x) := B 2 0 @ x 1 2 x 1 A, B(x) := 0 0 1 @ 0 0A ; ν (0,1), B 0 B John60, Edinburgh, June 2008 p.14/20

Some results (with J. Dolbeault and M. Loss) V ν = ν x, A B(x) := B 2 0 @ x 1 2 x 1 A, B(x) := 0 0 1 @ 0 0A ; ν (0,1), B 0 B For B = 0, λ 1 (0, V ν ) = 1 ν 2 ( 1,1) John60, Edinburgh, June 2008 p.14/20

Some results (with J. Dolbeault and M. Loss) V ν = ν x, A B(x) := B 2 0 @ x 1 2 x 1 A, B(x) := 0 0 1 @ 0 0A ; ν (0,1), B 0 B For B = 0, λ 1 (0, V ν ) = 1 ν 2 ( 1,1) For all B 0, λ 1 (B, V ν ) < 1 John60, Edinburgh, June 2008 p.14/20

Some results (with J. Dolbeault and M. Loss) V ν = ν x, A B(x) := B 2 0 @ x 1 2 x 1 A, B(x) := 0 0 1 @ 0 0A ; ν (0,1), B 0 B For B = 0, λ 1 (0, V ν ) = 1 ν 2 ( 1,1) For all B 0, λ 1 (B, V ν ) < 1 For all ν (0,1) there exists a critical field strength B(ν) such that λ 1 (B, V ν ) 1 if B B(ν) lim ν 1 B(ν) > 0, lim ν 0 ν log B(ν) = π John60, Edinburgh, June 2008 p.14/20

A better method to determine B(ν) IR3 (σ B )ϕ 2 1 + λ 1 (B, V ν ) + ν x dx + (1 λ 1 (B, V ν )) ϕ 2 dx IR 3 IR 3 ν x ϕ 2 dx John60, Edinburgh, June 2008 p.15/20

A better method to determine B(ν) IR3 (σ B )ϕ 2 1 + λ 1 (B, V ν ) + ν x dx + (1 λ 1 (B, V ν )) ϕ 2 dx IR 3 IR 3 ν x ϕ 2 dx and we are looking for B n B(ν) such that λ 1 (B n, ν) 1. If everything were compact, we would be able to pass to the limit and obtain IR3 x (σ B )ϕ 2 ν ν IR 3 x ϕ 2 dx + 2 ϕ 2 dx 0 IR 3 Now define the functional E B,ν [φ] := IR 3 x ν (σ B) φ 2 dx IR 3 ν x φ 2 dx, If everything were compact and nice", µ B,ν + 2 = 0 ; µ B,ν := inf j E B,ν [φ]; ff ϕ 2 dx = 1. IR 3 John60, Edinburgh, June 2008 p.15/20

If everything were compact and nice", µ B,ν + 2 = 0 ; µ B,ν := inf j E B,ν [φ]; ff ϕ 2 dx = 1. IR 3 John60, Edinburgh, June 2008 p.16/20

If everything were compact and nice", µ B,ν + 2 = 0 ; µ B,ν := inf j E B,ν [φ]; ff ϕ 2 dx = 1. IR 3 A very nice property is that the scaling φ B := B 3/4 φ `B 1/2 x preserves the L 2 norm and E B,ν [φ B ] = B E 1,ν [φ]. So, if we define µ(ν) := inf 0 φ C 0 (IR 3 ) we have µ B,ν = B µ(ν). E 1,ν [φ] φ 2 L 2 (R 3 ), THM : p B(ν) µ(ν) + 2 = 0 which is equivalent to B(ν) = 4 µ(ν) 2. PROPOSITION. On the interval (0, 1), the function ν µ(ν) is continuous, monotone decreasing and takes only negative real values. John60, Edinburgh, June 2008 p.16/20

The Landau level approximation Consider the class of functions A(B, ν) : φ l := B 2 π 2 l l! (x 2 + i x 1 ) l e B s2 /4 1, l N, s 2 = x 2 1 + x 2 2, 0 where the coefficients depend only on x 3, i.e., φ(x) = X l f l (x 3 ) φ l (x 1, x 2 ), z := x 3. Now, we shall restrict the functional E B,ν to the first Landau level. In this framework, that we shall call the Landau level ansatz, we also define a critical field by B L (ν) := inf j ff B > 0 : liminf bրb λl 1 (b, ν) = 1, where λ L 1 (b, ν) := inf λ[φ, b, ν]. φ A(B,ν), Π φ=0 John60, Edinburgh, June 2008 p.17/20

THEOREM : B L (ν) = 4 µ L (ν) 2, where µ L (ν) := inf f L ν [f] f 2 L 2 (R + ) < 0. John60, Edinburgh, June 2008 p.18/20

THEOREM : B L (ν) = 4 µ L (ν) 2, where µ L (ν) := inf f L ν [f] f 2 L 2 (R + ) < 0. L ν [f] = E 1,ν [φ f ], φ f (x) = f(z) e s2 /4 1. 2 π 0 John60, Edinburgh, June 2008 p.18/20

THEOREM : B L (ν) = 4 µ L (ν) 2, where µ L (ν) := inf f L ν [f] f 2 L 2 (R + ) < 0. L ν [f] = E 1,ν [φ f ], φ f (x) = f(z) e s2 /4 1. 2 π 0 L ν [f] = 1 ν 0 b(z) f 2 dz ν 0 a(z) f 2 dz b(z) = 0 p s 2 + z 2 s e s2 /2 ds and a(z) = 0 s e s2 /2 s 2 + z 2 ds. John60, Edinburgh, June 2008 p.18/20

Final results THEOREM. For ν (0, ν 0 ), B L (ν + ν 3/2 ) B(ν) B L (ν) John60, Edinburgh, June 2008 p.19/20

Final results THEOREM. For ν (0, ν 0 ), B L (ν + ν 3/2 ) B(ν) B L (ν) THEOREM. lim ν log B L (ν) = π. ν 0 COROLLARY. lim ν log B(ν) = π. ν 0 John60, Edinburgh, June 2008 p.19/20

Final results THEOREM. For ν (0, ν 0 ), B L (ν + ν 3/2 ) B(ν) B L (ν) THEOREM. lim ν log B L (ν) = π. ν 0 COROLLARY. lim ν log B(ν) = π. ν 0 B B(ν) B L (ν) 0.5 0.6 0.7 0.8 0.9 300 250 200 150 100 50 ν John60, Edinburgh, June 2008 p.19/20

Final results THEOREM. For ν (0, ν 0 ), B L (ν + ν 3/2 ) B(ν) B L (ν) THEOREM. lim ν log B L (ν) = π. ν 0 COROLLARY. lim ν log B(ν) = π. ν 0 B B(ν) B L (ν) 0.5 0.6 0.7 0.8 0.9 300 250 200 150 100 50 ν NUMERICAL OBSERVATION. For ν near 1, B(ν) is below B L (ν) by 30%. John60, Edinburgh, June 2008 p.19/20

Dear John : even if late, John60, Edinburgh, June 2008 p.20/20

Dear John : even if late, BON ANNIVERSAIRE! HAPPY BIRTHDAY! John60, Edinburgh, June 2008 p.20/20