Non analyticity of the ground state energy of the Hamiltonian for Hydrogen atom in nonrelativistic QED

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1 Non analyticity of the ground state energy of the Hamiltonian for Hydrogen atom in nonrelativistic QED Jean-Marie Barbaroux, Semjon Vugalter To cite this version: Jean-Marie Barbaroux, Semjon Vugalter. Non analyticity of the ground state energy of the Hamiltonian for Hydrogen atom in nonrelativistic QED. Journal of Physics A: Mathematical Theoretical, IOP Publishing, 2010, 43 (47, pp < / /43/47/474004>. <hal > HAL Id: hal Submitted on 1 Jun 2010 HAL is a multi-disciplinary open access archive for the deposit dissemination of scientific research documents, whether they are published or not. The documents may come from teaching research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2 NON ANALYTICITY OF THE GROUND STATE ENERGY OF THE HAMILTONIAN FOR HYDROGEN ATOM IN NONRELATIVISTIC QED J.-M. BARBAROUX 1, S.A. VUGALTER 2, Abstract. We derive the ground state energy up to the fourth order in the fine structure constant α for the translation invariant Pauli-Fierz Hamiltonian for a spinless electron coupled to the quantized radiation field. As a consequence, we obtain the non-analyticity of the ground state energy of the Pauli-Fierz operator for a single particle in the Coulomb field of a nucleus. 1. Introduction We study the translation invariant Pauli-Fierz Hamiltonian describing a spinless electron interacting with the quantized electromagnetic radiation field. In the last fifteen years, a large number of rigorous results were obtained concerning the spectral properties of Pauli-Fierz operators, starting with the pioneering works of Bach, Fröhlich Sigal [5, 3, 4]. In particular, the ground state energy were intensively studied ([15], [19], [17], [12], [9], [8], [16], [14]. One of the problems recently discussed is the existence of an expansion in powers of the fine structure constant α for the ground state energy of Pauli-Fierz operators. The very first results in this direction are due to Pizzo [20] later on Bach, Fröhlich Pizzo [2], where the operator for the Hydrogen atom is considered. In [2], a sophisticated rigorous renormalization group analysis is developed in order to determine the ground state energy, up to any arbitrary precision in powers of α, with an expansion of the form ε 0 + 2N k=1 ε(kα k/2 + o(α N, for any given N, where the coefficients ε k (α may diverge as α 0, but are smaller in magnitude than any power of α 1. The recursive algorithms developed in [2] are highly complex, explicitly computing the ground state energy to any subleading order of α is an extensive task. In the physical model where the photon form factor in the quantized electromagnetic vector potential contains the critical frequency space singularity responsible for the infamous infrared problem, it is expected that the rate of divergence of some of these coefficient functions ε k (α is proportional to log α 1. However, this is not explicitly exhibited in the current literature; for instance, it can a priori not be ruled out that terms involving logarithmic corrections cancel mutually. Moreover, for some models with a mild infrared behavior [14], the ground state energy is proven to be analytic in α (see also [18]. In a recent paper [7] Chen, Vougalter the present authors study the binding energy for Hydrogen atom, which is the difference between the infimum Σ 0 of the spectrum of the translationally invariant operator the infimum Σ of the 1

3 2 J.-M. BARBAROUX 1, S.A. VUGALTER 2, spectrum of the operator with Coulomb potential. It is shown in [7] that the binding energy as the form (1 Σ 0 Σ = α2 4 + e(1 α 3 + e (2 α 4 + e (3 α 5 log α 1 + o(α 5 log α 1, where the coefficients e (1, e (2 e (3 are independent of α explicitly computed. A natural question thus arose in the community, to know wether the logarithmic divergent term in (1 stemmed from Σ, Σ 0 or both. This question can not be answered on the basis of the computations done in [7], because we did not compute separately the value of Σ Σ 0, but their difference. Although the value of Σ 0 was known up to the order α 3 from earlier work [6], this did not allow us to answer the above question. In the work at h, we compute the infimum Σ 0 of the spectrum of the translationally invariant operator, up to the order α 4 with error O(α 5, derive Σ up to the order α 4, show that the logarithmic term in (1 is related to Σ not to Σ The model We study a non-relativistic free spinless electron interacting with the quantized electromagnetic field in Coulomb gauge. The Hilbert space accounting for the pure states of the electron is given by L 2 (R 3, where we neglect its spin. The Fock space of the transverse photons is F = n N F n, where the n-photon space F n = n ( s L 2 (R 3 C 2 is the symmetric tensor product of n copies of one-photon Hilbert spaces L 2 (R 3 C 2. The factor C 2 accounts for the two independent transversal polarizations of the photon. On F, we introduce creation annihilation operators a λ (k, a λ(k satisfying the distributional commutation relations [ a λ (k, a λ (k ] = δ λ,λ δ(k k, [ a λ (k, a λ (k ] = 0, where a λ denotes either a λ or a λ. There exists a unique unit ray Ω f F, the Fock vacuum, which satisfies a λ (k Ω f = 0 for all k R 3 λ {1, 2}. The Hilbert space of states of the system consisting of both the electron the radiation field is given by H := L 2 (R 3 F. We shall use units such that = c = 1, where the mass of the electron equals m = 1/2. The electron charge is then given by e = α. The Hamiltonian of the system is given by T = I el H f + : (i x I f αa(x 2 :, where : ( : denotes normal ordering. The free photon field energy operator H f is given by H f = k a λ(ka λ (kdk. R 3 λ=1,2 The magnetic vector potential is A(x = A (x + A + (x,

4 NON ANALYTICITY OF THE GROUND STATE ENERGY IN NRQED 3 where (2 A (x = λ=1,2 R 3 κ( k 2π k 1/2 ε λ(k e ikx a λ (k dk is the part of A(x containing the annihilation operators, A + (x = (A (x. The vectors ε λ (k R 3 are the two orthonormal polarization vectors perpendicular to k, ε 1 (k = (k 2, k 1, 0 k k 2 2 ε 2 (k = k k ε 1(k. In (2, the function κ implements an ultraviolet cutoff on the momentum k. We assume κ to be of class C 1, with compact support in { k Λ}, 0 κ 1 κ = 1 for k Λ 1. The ground state energy of T is denoted by Σ 0 := inf spec(t. We note that this system is translationally invariant; that is, T commutes with the operator of total momentum P tot = p el I f + I el P f, where p el P f denote respectively the electron the photon momentum operators. Therefore, for fixed value p R 3 of the total momentum, the restriction of T to the fibre space C F is given by (see e.g. [10] (3 T (p = : (p P f αa(0 2 : +H f, where by abuse of notation, we dropped all tensor products involving the identity operators I f I el. Henceforth, we will write It is proven in [1, 10] that A ± := A ± (0. Σ 0 = inf spec(t (0 is an eigenvalue of the operator T (0. We are now in position to state our first main result. On F we define respectively the positive bilinear form its associated seminorm (4 v, w := v, (H f + P 2 f w, v := v, v 1 2. Theorem 2.1 (Ground state energy of T T (0. We have (5 Σ 0 = d (0 α 2 + d (1 α 3 + d (2 α 4 + O(α 5, with d (0 := Φ 2 2 d (1 := 2 A Φ Φ Φ 1 2 ( 2 A d (2 Φ Φ Φ 3 2 := Φ Re Φ 1, A A Φ 3 +8 A Φ A Φ Φ Φ Φ 2 2 Φ 2 2,

5 4 J.-M. BARBAROUX 1, S.A. VUGALTER 2, (6 Φ 2 := (H f + P 2 f 1 A + A + Ω f, Φ 3 := (H f + P 2 f 1 P f A + Φ 2, Φ 1 := (H f + P 2 f 1 P f A Φ 2, Φ 2 := P Φ2 (H f + P 2 f 1 ( P f A + Φ 1 + P f A Φ A+ A Φ 2 Φ 4 := (H f + P 2 f 1 ( P f A + Φ A+ A + Φ 2, where P Φ2 is the orthogonal projection onto {ϕ F ϕ, Φ 2 = 0}. The proof of Theorem 2.1 is postponed to Section 4. The proof of the upper bound is derived in subsection 4.1 using a bona fide trial function, whereas the most difficult part, namely the proof of the lower bound, is given in subsection 4.2. Corollary 2.1 (non analyticity of inf spec(h. The Pauli-Fierz Hamiltonian for an electron interacting with a Coulomb electrostatic field coupled to the quantized radiation field is H := T α x. Its ground state energy Σ := inf spec(h fulfills where Σ = d (0 α 2 + d (1 α 3 + d (2 α 4 + d (3 α 5 log α 1 + o(α 5 log α 1, d (0 = d (0 1 4, d(1 = d (1 e (1, d(2 = d (2 e (2, d(3 = e (3, with e (1 = 2 π 0 κ 2 (t 1 + t dt, e (2 = 2 3 Re i=1 3 (A i (H f + Pf 2 1 A +.A + Ω f, (H f + Pf 2 1 (A + i Ω f i=1 3 ( (H f + Pf A +.P f (H f + Pf 2 1 (A + i Pf i (H f + Pf 2 1 A +.A + Ω f 2 3 i=1 A (H f + P 2 f 1 (A + i Ω f 2 + 4a 2 0 Q 1 ( 1 x u1 2, a 0 = k k 2 2 4π 2 k 3 2 k 2 + k κ( k dk 1dk 2 dk 3, e (3 = 1 3π ( 1 x u1 2, Q 1 is the projection onto the orthogonal complement to the ground state u 1 of the Schrödinger operator 1 x.

6 NON ANALYTICITY OF THE GROUND STATE ENERGY IN NRQED 5 Proof. This is a direct consequence of the above Theorem 2.1 [7, Theorem 2.1]. The next main result gives an approximate ground state of T (0. Let Ψ be the ground state of T (0, normalized by the condition (7 Ψ, Ω f = 1. The existence of Ψ was proved in [1, 10]. We decompose the state Ψ according to its, -projections in the direction of Φ 1, Φ 2, Φ 2, Φ 3 Φ 4 its orthogonal part R. This gives (8 Ψ = Ω f + 2η 1 α 3 2 Φ1 + η 2 αφ 2 + η 2 α 2 Φ2 + 2η 3 α 3 2 Φ3 + η 4 α 2 Φ 4 + R, where the coefficients η i (i = 1, 2, 3, 4 η 2, the vector R are uniquely determined by the conditions (9 for i, j = 1, 2, 3, 4. Φ i, Φ j = Φ j 2 δ ij, Φ i, Φ 2 = 0, Φ j, R = 0, Φ 2, R = 0, Ω f, R = Ω f, Φ j = 0, Theorem 2.2 (Ground state of T (0. Let Ψ be the ground state of T (0, normalized by the condition Ψ, Ω f = 1. Then Ψ =Ω f + 2α 3 2 Φ1 + α(1 βαφ 2 + 4α 2 Φ2 + 2α 3 2 Φ3 + 4α 2 Φ 4 + R, (10 with β := 2 A Φ Φ Φ 3 2 Φ 2 2, R :=R + 2(η 1 1α 3 2 Φ1 + (η 2 (1 βααφ 2 + 2(η 3 1α 3 2 Φ3 + ( η 2 4α 2 Φ2 + (η 4 4α 2 Φ 4, where the coefficients η j (j = 1, 2, 3, 4 η 2 satisfy that there exists a finite constant c such that for all α, η 1,3 1 2 cα, η cα 2, η cα, η cα, with R, R = O(α, R, R = O(α 2. The proof of this theorem is given in subsection Photon number field energy bounds In order to derive the ground state energy for T (0, we need to derive some a priori expected photon number bound expected field energy bound for the ground state. As a consequence of Theorem 3.2 in [6], we have the following bound for the -norm of the remainder R of the ground state Ψ, as defined by (8. Proposition 3.1. There exists c < such that (11 (H f + P 2 f R, R c(1 + η η 4 2 α 4. Proof. In [6, Theorem 3.2] it is shown that for η 1, η 2 η 3 given by (8 (9, for r := Ψ Ω f 2η 1 α 3 2 Φ 1 η 2 αφ 2 2η 3 α 3 2 Φ 3, we have r = O(α 2. Therefore, using the decomposition (8 concludes the proof.

7 6 J.-M. BARBAROUX 1, S.A. VUGALTER 2, Proposition 3.2. Let (12 Θ := Ψ αη 2 Φ 2 2α 3 2 η1 Φ 1 2α 3 2 η3 Φ 3 Ω f, where the vectors Φ i (i = 1, 2, 3 are defined in (6 in Theorem 2.1 the coefficients η i (i = 1, 2, 3 are given by the decomposition of Ψ according to (8 the conditions (9. Then (13 Θ, N f Θ = O(α 3. Proof. According to [6, Theorem 3.2], we have (14 Θ 2 = O(α 4. Now we write (15 Θ, N f Θ = k <α a λ (kθ 2 dk + a λ (kθ 2 dk. k α The second term in the right h side of (15 is bounded as follows (16 a λ (kθ 2 1 dk = k k a λ(kθ 2 dk α 1 H 1 2 f Θ 2 = O(α 3, k α k α where we used (14. For the first term in the right h side of (15, we write (17 k <α ( 4 a λ (kθ 2 dk = k <α + α 3 η 1 2 k <α a λ (kψ 2 dk + α 2 η 2 2 k <α ( a λ (k Ψ αη 2 Φ 2 2α 3 2 η1 Φ 1 2α η3 Φ 3 dk k <α a λ (kφ 1 2 dk + α 3 η 3 2 a λ (kφ 2 2 dk k <α a λ (kφ 3 2 dk. Straightforward computations shows that the last three terms in the right h side of (17 are O(α 3. To estimate the first integral in the right h side of (17 we follow the strategy used in the proof of [6, Proposition 3.1] as explained below. For σ > 0, let T σ (p denote the fiber Hamiltonian regularized by an infrared cutoff implemented by replacing the ultraviolet cutoff function κ of (2 by a C 1 function κ σ with κ σ = κ on [σ,, κ σ (0 = 0, κ σ monotonically increasing on [0, σ]. Then, E σ (p := inf spec(t σ (p is a simple eigenvalue with eigenvector Ψ σ (p F [1, 10]. If p = 0, one has p E σ (p = 0 = 0 (see [1, 10]. In Formula (6.11 of [11], it is shown that (18 a λ (kψ σ (0 = (A + (B, where from (6.12 of [11], it follows that (19 (A C(k p E σ (0 = 0, that (20 (B = α κ σ( k k T σ (k E σ (0 + k (T σ(0 E σ (0ɛ λ (k p Ψ σ (0, if the electron spin is zero. Thus it follows immediately from (6.19 in [11] that a λ (kψ σ (0 c α κ σ( k 1 k 1 m ren,σ Ψ σ(0 cα κ σ( k Ψ σ (0, k

8 NON ANALYTICITY OF THE GROUND STATE ENERGY IN NRQED 7 for spin zero, where m ren,σ is the renormalized electron mass for p = 0 (see [1, 10], defined by (21 1 m ren,σ = 1 2 pψ σ (0, (T σ (0 E σ (0 p Ψ σ (0 Ψ σ (0 2. As proved in [1, 10], 1 < m ren,σ < 1 + cα uniformly in σ 0. Therefore, one can write a λ (kψ 2 dk = lim a λ (kψ σ k <α σ 0 k <α 2 dk (22 lim c α σ 0 k <α κ σ( k Ψ σ (0 2 dk = O(α 3, k where Ψ = s lim σ 0 Ψ σ (0 (see [1]. The inequalities (16 (22 conclude the proof. A straightforward consequence of this result is Corollary 3.1. For Θ defined as in (12 by Θ = Ψ αη 2 Φ 2 2α 3 2 η 1 Φ 1 2α 3 2 η 3 Φ 3 Ω f, we have (23 Θ 2 = O(α 3. We introduce the following notations: 4. Proof of Theorem 2.1 (24 (1 (2 (3 Φ 2 = Φ 2 + Φ 2 + Φ 2 := ( P Φ2 (H f + Pf 2 1 P f A + ( Φ 1 + PΦ2 (H f + Pf 2 1 P f A Φ 3 + (P Φ2 (H f + P 2f 1 12 A+ A Φ 2, (25 Φ 4 = Φ (1 4 + Φ (2 4 := ((H f + P 2 f 1 P f A + Φ 3 + ( 1 4 (H f + P 2 f 1 A + A + Φ 2. For n N we also define Γ (n as the orthogonal projection onto the n-photon space F n of the Fock space F, whereas Γ ( n shall denote the orthogonal projection onto k n F k. Finally, we set (26 R i := Γ (i R, for i = 1, 2, 3, 4, R k := Γ ( k R Proof of the upper bound. The proof of the upper bound in Theorem 2.1 is easily obtained by picking the trial function ( Ψ trial :=Ω f + 2α 3 2 Φ1 + α 1 α 2 A Φ Φ Φ 3 2 Φ 2 2 Φ 2 (27 + α 2 Φ2 + 2α 3 2 Φ3 + α 2 Φ 4.

9 8 J.-M. BARBAROUX 1, S.A. VUGALTER 2, We then compute Ψ trial, T (0Ψ trial / Ψ trial 2. yields Ψ trial, T (0Ψ trial = α 2 Φ α 3( 2 A Φ Φ Φ 1 2 A straightforward computation + α 4( 8Re Φ 1, A A Φ A Φ A Φ Φ Φ 4 2 ( α 4 4 Φ1 2 4 Φ A Φ O(α 5. Φ 2 Since Ψ trial 2 = 1 + α 2 Φ O(α 3, we thus obtain inf spec(t (0 Ψtrial, T (0Ψ trial Ψ trial 2 = α 2 Φ α 3( 2 A Φ Φ Φ α 4( 8Re Φ 1, A A Φ A Φ A Φ Φ Φ Φ 2 2 Φ 2 2 ( α 4 4 Φ1 2 4 Φ A Φ O(α 5, Φ 2 which concludes the proof of the upper bound Proof of the lower bound. Since T (0 = H f + : ( P f α 1 2 A(0 2 : =(H f +P 2 f +α 1 2 (Pf A + +A + P f +α 1 2 (Pf A +A P f +α(a + 2 +α(a 2 + 2αA + A we obtain (28 Ψ, T (0Ψ =Re Ψ, α 1 2 Pf A Ψ + Re Ψ, 2αA A Ψ + Ψ, 2αA + A Ψ + Ψ, (H f + P 2 f Ψ As in (8-(9, we decompose the ground state Ψ of T (0 as follows Ψ = Ω f + 2η 1 α 3 2 Φ1 + η 2 αφ 2 + η 2 α 2 Φ2 + 2η 3 α 3 2 Φ3 + η 4 α 2 Φ 4 + R. Each term in the right h side of (28 are estimated respectively in Lemmata A.2-A.5. We thus collect all terms that occur in Lemmata A.2-A.5, regroup them according to the following rearrangement, estimate them separately (29 Ψ, T (0Ψ = (I + (II + (III + (IV + (V + positive terms where the positive terms are a part of Ψ, (H f + Pf 2 Ψ (I = Terms with a pre-factor α 2 involving a remainder term R i, (II = Terms with a pre-factor α 2 not involving remainder terms R, (III = Terms with a pre-factor α 3, (IV = Terms with a prefactor α 4, (V = Terms with a pre-factor α 5 the terms O(α 5.

10 NON ANALYTICITY OF THE GROUND STATE ENERGY IN NRQED 9 Terms with a pre-factor α 2 involving a remainder term R i. (I := 8α 2 Re η 1 Φ (1 2, R 2 8α 2 Re η 3 Φ (2 2, R 2 8α 2 Re η 2 Φ (3 2, R 2 8α 2 Re η 2 Φ (2 4, R 4 8α 2 Re η 3 Φ (1 4, R 4 Terms with a pre-factor α 2 not involving remainder terms R: (30 (II := α 2 2Re η 2 Φ α 2 η 2 2 Φ 2 2 = α 2 Φ α 2 ( (Re η (Im η 2 2 α 2 Φ α 2 ( (Re η Terms with a pre-factor α 3. (31 (III := α 3( 8Re η 1 η 2 Φ η 1 2 Φ 1 2 8Re η 3 η 2 Φ η 3 2 Φ η 2 A Φ 2 2 = 4α 3 Φ 1 2 ( η1 η 2 2 η α 3 Φ 3 2 ( η3 η 2 2 η α 3 A Φ O(α 5. Since from Lemma A.1 we have η 2 = 1 + O(α, we get (Im η 2 2 = O(α 2 (Re η = 2(Re η O(α 2, thus η 2 2 = 1 + 2(Re η O(α 2. Together with (31, this yields (32 (III =α 3 ( 4 Φ Φ A Φ α 3 (Re η 2 1( 4 Φ Φ A Φ α 3 Φ 1 2 η 1 η α 3 Φ 3 2 η 3 η O(α 5. The first term in the right h side of (32 is the α 3 term in the equality (5, thus we leave it as it is. The last line in (32, which is positive, shall be used later to estimate the terms (I (IV. The second term in the right h side of (32 is estimated together with the term α 2 Φ 1 2 (Re η obtained in the lower bound (30 for (II. We obtain (33 (34 2α 3 (Re η 2 1(2 A Φ Φ Φ α 2 Φ 2 2 (Re η ( = α 2 α 2 A Φ Φ Φ (Re η 2 1 Φ 2 Φ 2 2 ( 2 A α 4 Φ Φ Φ 3 2 Φ 2 ( 2 A α 4 Φ Φ Φ Φ 2 Collecting estimates (30, (32 (33 yields (II + (III α 2 Φ α 3( 2 A Φ Φ Φ 3 2 ( 2 A α 4 Φ Φ Φ 3 2 Φ 2 + 4α 3 Φ 1 2 η 1 η α 3 Φ 3 2 η 3 η O(α

11 10 J.-M. BARBAROUX 1, S.A. VUGALTER 2, Terms with a pre-factor α 4. (35 (IV := 8α 4( Re η 1 η 2 Φ (1 2, Φ 2 + Re η 3 η 2 Φ (2 2, Φ 2 + Re η 2 η 2 Φ (3 2, Φ 2 + η 2 2 α 4 Φ 2 2 8α 4( Re η 2 η 4 Φ (2 4, Φ 4 + Re η 3 η 4 Φ (1 4, Φ 4 + η 4 2 α 4 Φ α 4 Re η 1 η 3 Φ 1, A A Φ η 1 2 α 4 A Φ η 3 2 α 4 A Φ 3 2. Let us first remark that in this expression, we have terms with pre-factor η 2 positive terms with pre-factor η 2 2, therefore, this implies that η 2 is uniformly bounded in α for a minimizer. The same remarks hold for η 4. Thus, there exists c < independent on α such that (36 η 2 c, η 4 c. Now, we add to the term (IV half of the positive term 4α 3 Φ 1 2 η 1 η α 3 Φ 3 2 η 3 η 2 2 obtained in the lower bound (34 for (II + (III, we split the resulting expression in three parts as follows (37 (IV + 2α 3 Φ 1 2 η 1 η α 3 Φ 3 2 η 3 η 2 2 =: (IV (1 + (IV (2 + (IV (3 + (IV (4, where (38 (IV (1 := 8α 4( Re η 1 η 2 Φ (1 2, Φ 2 + Re η 3 η 2 Φ (2 2, Φ 2 + Re η 2 η 2 Φ (3 2, Φ 2 + η 2 2 α 4 Φ α 3 Φ 1 2 η 1 η α 3 Φ 3 2 η 3 η 2 2, (39 (IV (2 := 8α 4( Re η 2 η 4 Φ (2 4, Φ 4 + Re η 3 η 4 Φ (1 4, Φ 4 + η 4 2 α 4 Φ α 3 Φ 3 2 η 3 η 2 2, (40 (IV (3 := 8α 4 Re η 1 η 3 Φ 1, A A Φ η 1 2 α 4 A Φ η 3 2 α 4 A Φ α 3 Φ 1 2 η 1 η α 3 Φ 3 2 η 3 η 2 2 Using from Lemma A.1 that η 2 = 1 + O(α the fact that η 4 is bounded uniformly in α (see (36 yields (41 (IV (2 = 8α 4 ( Re η 2 η 4 Φ (2 4, Φ 4 + Re η 2 η 4 Φ (1 4, Φ 4 8α 4 Re (η 3 η 2 η 4 Φ (1 4, Φ 4 + α 3 Φ 3 2 η 3 η η 4 2 α 4 Φ 4 2 = 8α 4 ( Re η 2 η 4 Φ (2 4, Φ 4 + Re η 2 η 4 Φ (1 4, Φ 4 cα 5 η η 4 2 α 4 Φ α 4 Φ 4 2 cα 5.

12 NON ANALYTICITY OF THE GROUND STATE ENERGY IN NRQED 11 (42 The term (IV (1 is treated as follows (IV (1 = 8α 4 Re (η 1 η 2 η 2 Φ (1 2, Φ 2 + 2α 3 Φ 1 2 η 1 η 2 2 8α 4 Re (η 3 η 2 η 2 Φ (2 2, Φ 2 + α 3 Φ 3 2 η 3 η 2 2 8α 4 Re η 2 η 2 Φ (1 2, Φ 2 8α 4 Re η 2 η 2 Φ (2 2, Φ 2 8α 4 Re η 2 η 2 Φ (3 2, Φ 2 + η 2 2 α 4 Φ 2 2. Since η 2 is bounded (see (36, the first line the second line in the right h side are of the order α 5. In addition, replacing η 2 by 1 + O(α (see Lemma A.1 in the third line of (42 yields (43 (IV (1 = ( 8α 4 Re η 2 Φ (1 2, Φ 2 + η 2 Φ (2 2, Φ 2 + η 2 Φ (3 2, Φ 2 + η 2 2 α 4 Φ O(α 5 = 8α 4 Re η 2 Φ η 2 2 α 4 Φ O(α 5 16α 4 Φ O(α 5. (44 Eventually, we estimate the term (IV (3. We have (IV (3 =8α 4 Re η 1 η 3 Φ 1, A A Φ α3 Φ 1 2 η 1 η α3 Φ 3 2 η 3 η η 1 2 α 4 A Φ α3 Φ 1 2 η 1 η η 3 2 α 4 A Φ α3 Φ 3 2 η 3 η 2 2 The first line in (44 is estimated as 8α 4 Re η 1 η 3 Φ 1, A A Φ α3 Φ 1 2 η 1 η α3 Φ 3 2 η 3 η 2 2 (45 = 8α 4 Re (η 1 η 2 η 3 Φ 1, A A Φ α3 Φ 1 2 η 1 η α 4 Re η 2 ( η 3 η 2 Φ 1, A A Φ α3 Φ 3 2 η 3 η α 4 Re η 2 2 Φ 1, A A Φ 3 cα 5 + 8α 4 Re Φ 1, A A Φ 3 where we used again η 2 2 = 1 + O(α η 3 = O(1. The second line in (44 is estimated as 8 η 1 2 α 4 A Φ α3 Φ 1 2 η 1 η 2 2 (46 = 8 η 2 2 α 4 A Φ ( η 1 2 η 2 2 α 4 A Φ α3 Φ 1 2 η 1 η 2 2 8α 4 A Φ O(α 5 96 η 1 η 2 α 4 A Φ α3 Φ 1 2 η 1 η 2 2 8α 4 A Φ O(α 5.

13 12 J.-M. BARBAROUX 1, S.A. VUGALTER 2, Similarly, the third line in (44 is estimated by (47 8 η 3 2 α 4 A Φ α3 Φ 3 2 η 3 η 2 2 8α 4 A Φ O(α 5. Collecting (45, (46 (47 yields (48 (IV (3 8α 4 Re Φ 1, A A Φ 3 + 8α 4 A Φ α 4 A Φ O(α 5. This inequality, together with (37, (41 (43 gives (49 (IV + 2α 3 Φ 1 2 η 1 η α 3 Φ 3 2 η 3 η 2 2 α 4( 8Re Φ 1, A A Φ A Φ A Φ Φ Φ O(α 5. Next, we can treat the term (I. For that sake, we add the remaining other half of the positive term 4α 3 Φ 1 2 η 1 η α 3 Φ 3 2 η 3 η 2 2 obtained in the lower bound (34 for (II + (III. Writing η 1 = (η 1 η 2 + η 2, η 3 = (η 3 η 2 + η 2, η 2 = 1 + O(α using the fact that Φ (1 2, R 2 + Φ (2 2, R 2 + Φ (3 2, R 2 = Φ 2, R 2 = 0, we get, following the same arguments as for the estimate of (IV (50 (I + 2α 3 Φ 1 2 η 1 η α 3 Φ 3 2 η 3 η 2 2 = O(α 5. Terms with a pre-factor α 5 the terms O(α 5. Collecting these terms yields the following result (51 (V := cα 5 ( η η η η η O(α 5 = O(α 5. The last equality holds since η 1, η 2, η 3 are bounded (Lemma A.1 since we proved in (36 that η 2 η 4 are also bounded. Collecting (34, (49 (50 (51 thus gives (52 Ψ, T (0Ψ = (I + (II + (III + (IV + (V α 2 Φ α 3( 2 A Φ Φ Φ 3 2 α 4 ( 4 Φ1 2 4 Φ A Φ 2 2 Φ 2 + α 4( 8Re Φ 1, A A Φ 3 +8 A Φ A Φ Φ Φ We conclude the proof of the lower bound for inf spec(t (0 by computing +O(α 5. (53 Ψ 2 =1 + 2η 1 α 3 2 Φ1 + R η 2 αφ 2 + η 2 α 2 Φ2 + R η 3 α 3 2 Φ3 + R α 2 η 4 Φ 4 + R 4 2 =1 + α 2 Φ O(α 3, where we used that η 1, η 3, η 2, η 4 are bounded (Lemma A.1 (36, that η 2 = 1+O(α (Lemma A.1, as a consequence of Corollary 3.1 that the following holds: R 1, R 2, R 3, R 4 = O(α 3 2.

14 NON ANALYTICITY OF THE GROUND STATE ENERGY IN NRQED Proof of Theorem 2.2. The proof of (10 is a consequence of the fact that inf spec(t (0 = Ψ, T (0Ψ / Ψ 2 the value ( of Ψ trial, T (0Ψ trial / Ψ trial 2 coincide up to O(α 5 for Ψ trial := Ω f +2α 3 2 Φ 1 +α 1 α 2 A Φ Φ Φ3 2 Φ 2 Φ α 2 Φ2 + 2α 3 2 Φ 3 + α 2 Φ 4. The properties for η 1, 3 η 2 were already established in [6] as reminded in Lemma A.1. The properties for η 2 η 4 come from the fact that η 2 η 4 minimize (52 up to O(α 5. The equality R = O(α 2 is given by Proposition 3.1. The equality R = O(α 2 is a consequence of R = O(α 2, the definition (10 for R, the - orthogonalities in (9. Finally, Corollary 3.1 proves R = O(α, which in turn implies R = O(α. Acknowledgments J.-M. B. S. A. V. thank the Institute for Mathematical Sciences the Centre of Quantum Technologies of the National University of Singapore, where this work was done. J.-M. B. also gratefully acknowledges financial support from Agence Nationale de la Recherche, via the project HAM-MARK ANR-09-BLAN Appendix A.1. Estimates on η 1, η 2 η 3. In the following lemma, we give an estimate of the coefficients η 1, η 2 η 3 that occur in the decomposition (8 of Ψ. Lemma A.1. We have (54 η 1 = 1 + O(α 1 2, η3 = 1 + O(α 1 2, η2 = 1 + O(α Proof. This is a direct consequence on the estimates of η 1, η 2 η 3 for the approximate ground state up to the order α 3 derived in [6], since, due to the conditions (9, the coefficients η 1, η 2 η 3 in the decomposition (8 of Ψ are the same as the coefficients η 1, η 2 η 3 in the decomposition [6, (10]. Note that there was a misprint in the estimates provided in [6] for η 1 1, η 2 1 η 3 1, since a square was missing. One should read in [6, Theorem 3.2], η 1,3 1 2 cα η cα 2. A.2. Estimate of the term Re Ψ, 4α 1 2 P f A Ψ. Throughout this appendix, we shall always use the decomposition of Ψ given by (8-(9 (24-(25. Lemma A.2. We have Re Ψ, 4α 1 2 Pf A Ψ (H f + P 2 f R, R (55 8α 3 Re η 1 η 2 Φ 1 2 8α 3 Re η 2 η 3 Φ 3 2 8α 4 Re η 2 η 1 Φ 2, (1 Φ 2 8α 4 (2 Re η 2 η 3 Φ 2, Φ 2 8α 4 Re η 3 η 4 Φ (1 4, Φ 4 8α 2 Re η 1 Φ (1 2, R 2 8α 2 Re η 3 Φ (2 2, R 2 8Re η 3 α 2 Φ (1 4, R 4 c(1 + η η η 4 2 α 5.

15 14 J.-M. BARBAROUX 1, S.A. VUGALTER 2, Proof. Using the decomposition (8-(9 of the ground state Ψ, we obtain Re Ψ, 4α 1 2 Pf A Ψ = Re R 1, (4α 1 2 Pf A η 2 αφ 2 + 4α 1 2 Pf A η 2 α 2 Φ2 + 4α 1 2 Pf A R 2 + Re 2η 1 α 3 2 Φ1, (4α 1 2 Pf A η 2 αφ 2 + 4α 1 2 Pf A η 2 α 2 Φ2 + 4α 1 2 Pf A R 2 + Re η 2 α 2 Φ 2, (4α 1 2 Pf A 2η 3 α 3 2 Φ3 + 4P f A R 3 + Re η 2 α 2 Φ2, (4α 1 2 Pf A 2η 3 α 3 2 Φ3 + 4α 1 2 Pf A R 3 + Re R 2, (4α 1 2 Pf A 2η 3 α 3 2 Φ3 + 4α 1 2 Pf A R 3 + Re 2η 3 α 3 2 Φ3, (4α 1 2 Pf A η 4 α 2 Φ 4 + 4α 1 2 Pf A R 4 + Re R 3, (4α 1 2 Pf A η 4 α 2 Φ 4 + 4Re α 1 2 Pf A R 4 + Re Γ ( 4 Ψ, 4α 1 2 Pf A Γ ( 5 Ψ. For each value of n, we collect separately the terms in the right h side of this equality that stem from Re Γ (n Ψ, 4α 1 2 P f A Γ (n+1 Ψ. For estimating some of these terms, like in (57 or (58, we shall add a term like ɛ H f R, R or ɛ Pf 2 R, R borrowed from the left h side of (55. - For n = 0 there is no contribution. - For n = 1, we obtain the terms (56 Re R 1, 4α 1 2 Pf A η 2 αφ 2 = 4α 3 2 Re η2 R 1, Φ 1 = 0, where we used the, -orthogonality of R 1 Φ 1 given by (9, (57 Re R 1, 4α 1 2 Pf A η 2 α 2 Φ P 2 f R 1, R 1 4 P f R 1 A Φ2 α 5 2 η P f R 1 2 = ( 1 4 P f R 1 8α 5 2 η2 A Φ A Φ2 2 η 2 2 α 5 c η 2 2 α 5. Note that we shall use the above argument several times in this proof, as well as in the proof of the other lemmata of this Appendix. We shall not give details again in these other cases. We also have the following terms (58 Re R 1, 4α 1 2 Pf A R P 2 f R 1, R H f R 2, R 2 cα 1 2 Pf R 1 2 cα 1 2 A R P 2 f R 1, R H f R 2, R 2 0, where we used from [15, Lemma A4] the inequality A R 2 c H 1 2 f R 2, (59 (60 Re 2η 1 α 3 2 Φ1, 4α 1 2 Pf A η 2 αφ 2 = 8α 3 Re η 1 η 2 Φ 1, P f A Φ 2 = 8α 3 Re η 1 η 2 Φ 1 2, Re 2η 1 α 3 2 Φ1, 4α 1 2 Pf A η 2 α 2 Φ2 = 8α 4 Re η 1 η 2 Φ 1, P f A Φ2 = 8α 4 Re η 1 η 2 Φ (1 2, Φ 2,

16 NON ANALYTICITY OF THE GROUND STATE ENERGY IN NRQED 15 (61 (62 Re 2η 1 α 3 2 Φ1, 4α 1 2 Pf A R 2 = 8α 2 Re η 1 (H f + P 2 f P f A + Φ 1, P Φ2 R 2 - For n = 2, we obtain the terms = 8α 2 Re η 1 Φ (1 2, R 2. Re η 2 αφ 2, 4α 1 2 Pf A 2η 3 α 3 2 Φ3 = 8α 3 Re η 2 η 3 Φ 3 2, (63 (64 (65 Re η 2 α 2 Φ 2, 4P f A R 3 = 4α 3 2 Re η2 Φ 3, R 3 = 0, Re η 2 α 2 Φ2, 4α 1 2 Pf A 2η 3 α 3 2 Φ3 = 8α 4 Re η 2 η 3 Φ 2, Φ (2 2, Re η 2 α 2 Φ2, 4α 1 2 Pf A R P 2 f R 3, R 3 c η 2 2 α 5, where we used from [15, Lemma A4] that A R 3 c H 1 2 f R 3, (66 Re R 2, 4α 1 2 Pf A 2η 3 α 3 2 Φ3 = 8α 2 Re η 3 R 2, Φ (2 2, (67 Re R 2, 4α 1 2 Pf A R P f 2 R 2, R H f R 3, R 3 0, with similar argument as for(58 for the last inequality. - For n = 3, we obtain the terms (68 (69 (70 (71 Re 2η 3 α 3 2 Φ3, 4α 1 2 Pf A η 4 α 2 Φ 4 = 8α 4 Re η 3 η 4 Φ (1 4, Φ 4, Re 2η 3 α 3 2 Φ3, 4α 1 2 Pf A R 4 = 8Re η 3 α 2 Φ (1 4, R 4, Re R 3, 4α 1 2 Pf A η 4 α 2 Φ P 2 f R 3, R 3 c η 4 2 α 5, Re R 3, 4Re α 1 2 Pf A R P 2 f R 3, R H f R 4, R All contributions to the terms with n 4, give (72 Re Γ ( 4 Ψ, 4α 1 2 Pf A Γ ( 5 Ψ H f Γ ( 5 Ψ, Γ ( 5 Ψ cα P f Γ ( 4 Ψ 2 = cα 5 (1 + η η 4 2, where we used (11 of Proposition 3.1. Collecting the inequalities (56-(72 conclude the proof of the Lemma. A.3. Estimate of the term Re Ψ, 2αA A Ψ. Lemma A.3. We have Re Ψ, 2αA A Ψ (H f + P 2 f R, R (73 2 α 2 Re η 2 Φ α 2 Re η 2 Φ (2 4, R α 4 Re η 1 η 3 Φ 1, A A Φ 3 8 α 4 Re η 2 η 4 Φ (2 4, Φ 4 c(1 + η η η η 4 2 α 5

17 16 J.-M. BARBAROUX 1, S.A. VUGALTER 2, Proof. Using the decomposition (8-(9 of the ground state Ψ yields Re Ψ, 2αA A Ψ = Re Ω f, (2αA A η 2 αφ 2 + 2αA A η 2 α 2 Φ2 + 2αA A R 2 + Re 2η 1 α 3 2 Φ1, (2αA A 2η 3 α 3 2 Φ3 + 2αA A R 3 + Re R 1, (2αA A 2η 3 α 3 2 Φ3 + 2αA A R 3 + Re η 2 αφ 2, (2αA A η 4 α 2 Φ 4 + 2αA A R 4 + Re η 2 α 2 Φ2, (2αA A η 4 α 2 Φ 4 + 2Re αa A R 4 + Re R 2, (2αA A η 4 α 2 Φ 4 + 2αA A R 4 + Re 2η 3 α 3 2 Φ3, 2αA A R 5 + Re R 3, 2αA A R 5 + Re Γ n 4 Ψ, 2αA A R 6. We collect in this expression the different contributions in Re Γ (n Ψ, 2αA A Γ (n+2 Ψ for each value of n. We shall use throughout this proof very similar arguments to those used in the proof of Lemma A.2. - For n = 0, we have the terms (74 (75 (76 (77 (78 (79 Re Ω f, 2αA A η 2 αφ 2 = 2 α 2 Re η 2 Φ 2 2, Re Ω f, 2αA A η 2 α 2 Φ2 = 2α 3 Re η 2 Φ 2, Φ 2 = 0, Re Ω f, 2αA A R 2 = 2αRe Φ 2, R 2 = 0, - For n = 1, we have the terms Re 2η 1 α 3 2 Φ1, 2αA A 2η 3 α 3 2 Φ3 = 8 α 4 Re η 1 η 3 Φ 1, A A Φ 3, Re 2η 1 α 3 2 Φ1, 2αA A R H f R 3, R 3 c η 1 2 α 5, Re R 1, 2αA A 2η 3 α 3 2 Φ H f R 1, R 1 = Re H 1 2 f R 1, H 1 2 f 2αA A 2η 3 α 3 2 Φ H f R 1, R 1 c η 3 2 α 5,, using (13 of Proposition 3.2 [15, Lemma A4] (80 Re R 1, 2αA A R H f R 3, R 3 5 cα A + R 1 H 1 2 f R H 1 2 f R 3 2 ( cα 2 A + R H 1 2 f R H 1 2 f R 3 2 cα 2 ( R H 1 2 f R 1 2 cα 5 (1 + η η 4 2 (81 (82 (83 (84 - For n = 2, we have the terms Re η 2 αφ 2, 2αA A η 4 α 2 Φ 4 = 8α 4 Re η 2 η 4 Φ (2 4, Φ 4, Re η 2 αφ 2, 2αA A R 4 = 8α 2 Re η 2 Φ (2 4, R 4, Re η 2 α 2 Φ2, 2αA A η 4 α 2 Φ 4 c α 5 ( η η 4 2 Re η 2 α 2 Φ2, 2Re αa A R 4 c α 5 (1 + η η 4 2,

18 NON ANALYTICITY OF THE GROUND STATE ENERGY IN NRQED 17 using A R 4 c H 1 2 f R 4 cα 5 (1 + η η 4 2 (respectively [15, Lemma A4] Proposition 3.1. We also have the terms (85 (86 Re R 2, 2αA A η 4 α 2 Φ H f R 2, R 2 = Re H 1 2 f R 2, 2αH 1 2 f A A η 4 α 2 Φ H f R 2, R 2 c η 4 2 α 6 Re R 2, 2αA A R H f R 4, R 4 cα 2 A + R 2 2 cα 2 ( H f R R 2 2 cα 2 ( R Θ 2 + η 2 2 α 2 Φ2 2 + η 4 2 α 2 Φ 4 2 cα 5 (1 + η η 4 2, for Θ defined by (12 using from (23 of Corollary 3.1 that Θ 2 = O(α 3 from (11 of Proposition 3.1 that R 2 2 cα 4 (1 + η η For n 3 we collect all the terms as follows (87 Re 2η 3 α 3 2 Φ3, 2αA A R H f R 5, R 5 c η 3 2 α 5, (88 Re R 3, 2αA A R H f R 5, R 5 cα 5, using (23 of Corollary 3.1 in the last inequality. Finally, we get (89 Re Γ n 4 Ψ, 2αA A R H f R 6, R 6 cα 5 (1 + η η 4 2, Collecting (74-(89 yields the result. A.4. Estimate of the term Ψ, 2αA + A Ψ. Lemma A.4. We have (90 Ψ, 2αA + A Ψ (H f + P 2 f R, R 8α 2 Re η 2 R 2, + 8α 4 η 1 2 A Φ α 4 η 3 2 A Φ 3 2 8α 4 Re η 2 η 2 Φ 2, cα 5 (1 + η η η 2 2. Proof. With the decomposition (8-(9 of Ψ we get Φ ( η 2 2 α 3 A Φ 2 2 Φ (3 2 Ψ, 2αA + A + Ψ = 2η 1 α 3 2 Φ1, 2αA + A 2η 1 α 3 2 Φ1 + 2Re 2η 1 α 3 2 Φ1, 2αA + A R 1 + η 2 αφ 2, 2αA + A η 2 αφ 2 + 2Re η 2 αφ 2, 2αA + A η 2 α 2 Φ2 + η 2 α 2 Φ2, 2αA + A η 2 α 2 Φ2 + R 2, 2αA + A R 2 + 2Re R 2, 2αA + A η 2 Φ 2 + 2Re R 2, 2αA + A η 2 α 2 Φ( η 3α 3 2 Φ3, 2αA + A 2η 3 α 3 2 Φ3 + 2Re 2η 3 α 3 2 Φ3, 2αA + A R 3 + R 3, 2αA + A R 3 + Γ ( 4 Ψ, 2αA + A Γ ( 4 Ψ. For each value of n, we next collect in the above equality the different contributions of Γ (n Ψ, 2αA + A Γ (n Ψ. - For n = 0, there is no term. - For n = 1, we have (91 2η 1 α 3 2 Φ1, 2αA + A 2η 1 α 3 2 Φ1 = 8 η 1 2 α 4 A Φ 1 2,

19 18 J.-M. BARBAROUX 1, S.A. VUGALTER 2, (92 2Re 2η 1 α 3 2 Φ1, 2αA + A R H f R 1, R 1 c η 1 2 α 5. - For n = 2, we obtain (93 (94 (95 (96 η 2 αφ 2, 2αA + A η 2 αφ 2 = 2 η 2 2 α 3 A Φ 2 2, 2Re η 2 αφ 2, 2αA + A η 2 α 2 Φ2 = 8Re η 2 η 2 α 4 Φ (3 2, Φ 2, η 2 α 2 Φ2, 2αA + A η 2 α 2 Φ2 = 4α 5 η 2 2 A Φ2 2, R 2, 2αA + A R 2 0, (97 2Re R 2, 2αA + A η 2 Φ 2 = 8α 2 Re η 2 R 2, Φ (3 2, (98 2Re R 2, 2αA + A η 2 α 2 Φ( H f R 2, R 2 c η 2 2 α 5. - For n = 3, we have (99 (100 2η 3 α 3 2 Φ3, 2αA + A 2η 3 α 3 2 Φ3 = 8α 4 η 3 2 A Φ 3 2, 2Re 2η 3 α 3 2 Φ3, 2αA + A R H f R 3, R 3 η 3 2 α 5, (101 R 3, 2αA + A R 3 0, - For n 4, we obtain (102 Γ ( 4 Ψ, 2αA + A Γ ( 4 Ψ 0. Collecting (91-(102 concludes the proof of the lemma. A.5. Computation of the term Ψ, H f + P 2 f Ψ. Lemma A.5. We have (103 (H f + P 2 f Ψ, Ψ = η 2 2 α 2 Φ η 1 2 α 3 Φ η 3 2 α 3 Φ η 2 2 α 4 Φ η 4 2 α 4 Φ R 2. Proof. Using the decomposition (8 of Ψ using the whole set of orthogonalities with respect to, given in (9, we obtain that all crossed terms are zero. The proof is thus straightforward. References [1] V. Bach, T. Chen, J. Fröhlich, I. M. Sigal The renormalized electron mass in non-relativistic QED, J. Funct. Anal., 243 (2, (2007. [2] V. Bach, J. Fröhlich, A. Pizzo, Infrared-finite algorithms in QED: the groundstate of an atom interacting with the quantized radiation field, Comm. Math. Phys. 264, no. 1, (2006. [3] V. Bach, J Fröhlich, I. M. Sigal, Spectral analysis for systems of atoms molecules coupled to the quantized radiation field, Comm. Math. Phys. 207, no. 2, (1999. [4] V. Bach, J. Fröhlich, I. M. Sigal, Quantum electrodynamics of confined nonrelativistic particles, Adv. Math. 137, no. 2, (1998. [5] V. Bach, J. Fröhlich, I. M. Sigal, Mathematical theory of nonrelativistic matter radiation, Lett. Math. Phys. 34, no. 3, (1995. [6] J.-M. Barbaroux, T. Chen, V. Vougalter, S.A. Vugalter, On the ground state energy of the translation invariant Pauli-Fierz model, Proc. Amer. Math. Soc. 136, (2008.

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