Recent Developments and Applications of Integral Transforms in Few- and Many-Body Physics

Transcription

1 Recent Developments and Applications of Integral Transforms in Few- and Many-Body Physics Outline Introduction Compton scattering (A=2) Δ degrees of freedom in 3He(e,e') (A=3) Role of 0+ resonance in 4He(e,e') (A=4) Density excitation response in bulk atomic 4He at T=0

2 Introduction Consider an observable R(E) and an integral transform ( ): ( ) = de K(,E) R(E) with some kernel K(,E) Often it is easier to calculate ( ) than R(E). Then the observable R(E) can be obtained via inversion of the integral transform. In order to make the inversion sufficiently stable the kernel K(,E) should resemble a kind of energy filter (Lorentzians, Gaussians,...); best choice would be a -function.

3 In the following we will consider LITs (Lorentz integral transforms) with K(,E) = [(E- R)2 + I2]-1 and Sumudu transforms with KP(,E) = Ν ( e µ Ε/σ e ν Ε/σ )P

4 Photon Scattering with the LIT method (more details in G. Bampa, WL, H. Arenhӧvel, PRC 84, )

5 Photon scattering The photon scattering amplitude is given by two terms: The contact or two photon amplitude (TPA) B (k',k) and the ' resonance amplitude (RA) R (k',k) '

6 total scattering amplitude: TPA has the form: RA is given by with intermediate propagator Cartesian tensor operator B of rank 2 represents the second order term of the e.m. interaction

7 Current operator Intrinsic current j plus a term taking into account the convection current of the separated cm-motion (M: nucleon mass, A: mass number of nucleus) The intrinsic charge and current operators consist of one- and two- body parts el, ml, pl, and l: charge, magnetic moment, internal momentum, and spin operator of l-th particle

8 Low-energy limits Resulting in the low-energy limit for the total scattering amplitude: which is the classical Thomson limit

9 Reaction strength is described by polarizabilities M0: electric multipole, M1: magnetic multipole incoming photon transfers angular momentum L scattered photon transfers angular momentum L' total momentum transfer J to the nucleus with L-L' J L+L'

10 Expansion of total scattering amplitude in terms of polarizabilities where (Ii, Mi) and (Jf, Mf) refer to the angular momenta and their projections on the quantization axis of the initial and final states. The polarizabilities can be separated in a TPA and a RA contribution

11 Polarizability contribution for resonance amplitude: (small cm current contribution neglected) Polarizability contribution for two-photon amplitude: Evaluation of the TPA contribution is straight forward once the TPA operator B(x,y) is given

12 For the RA contribution one finds by evaluating the reduced matrix element in standard fashion Calculation of the RA part is more involved! One has to sum over all possible intermediate states In> and energies En For k=0 only the scalar E1-E1 polarizability is nonvanishing: (I is ground-state spin)

13 The scattering cross section with E1 transitions only: with

14 Application of the LIT method Introduction of a polarizability strength function In general the strength funcion is off-energy shell: E Ei + k. One finds: (I,E) is density of states for energy E and angular momentum J Polarizability becomes

15 Consider a fixed intermediate total angular momentum state InMn> leads to following polarization strength

16 The partial strength function can be calculated with the LIT method One finds where the LIT state is obtained from

17 Deuteron Case for elastic scattering Calculation is made in the cm-system, where one has k=k' only the dominant E1 transistions are considered taking the long wave length approximation (Siegert form) Thus only the polarizabilities PJ(E1,E1,k) with J = 0, 1, 2 contribute E1 E1 polarization strength function:

18 LIT equation Expansion of LIT state leads to following radial equations: with resulting in three LITs

19 Inversion of LIT Lj( ) gives function Fj(E) and leads to polarization strength function Then one has the following polarizabilities Following results are obtained with Argonne v18 potential

20 Results for the LITs with I = 5 MeV j=0 j=1 j=2

21 Comparison of functions Fj with standard calculation for full E1-operator

22 Results for E1 E1 polarizabilities solid black lines: LIT results dotted blue line: full E1-operator dashed red line: inclusion of MEC (M. Weyrauch, H. Arenhövel, NPA 408, 425 (1983))

23 Cross section result Note real parts of polarizabilities are normalized for k = 0 to obtain the correct low-energy result, i.e. classical Thomson limit for J = 0 and Re(P2(k=0)) = 0 (implicit consideration of MEC contribution in both cases) klab=55 MeV

24 Δ degrees of freedom in 3He(e,e') With the LIT method more details in L. Yuan, WL, V.D. Efros, G. Orlandini, E.L. Tomusiak, PLB 706, 90 L. Yuan, V.D. Efros, WL, E.L. Tomusiak, PRC 82,

25 Schrödinger equation with degrees of freedom = N + (TN + VNN E) N = VNN,N (*) ( m + T + VN E) = VN,NN N =H VNN,N (VNN) and VN,NN (VN ) transition (diagonal) potentials between NN,N NNN and NN spaces (A=3), = (H E) 1 VN,NN N m = M MN (IA) (TN + VNN VNN,N (H E) 1 VN,NN E) N = 0 (**) realistic VNN Step 1: solve (**) with realistic VNN +3NF Step 2: solve in IA

26 LIT equation with degrees of freedom ~= ~ +~ N (TN + VNN ) ~ N = VNN,N ~ + ONN 0,N + ON 0, ( m + T + VN ) ~ = VN,NN ~ + O N 0,N +O 0, =H VNN,N (VNN) and VN,NN (VN ) transition (diagonal) potentials between NN,N NNN and NN spaces (A=3), m = M MN

27 LIT equation with degrees of freedom ~= ~ +~ N (TN + VNN ) ~ N = VNN,N ~ + ONN 0,N + ON 0, ( m + T + VN ) ~ = VN,NN ~ + O N 0,N +O 0, =H VNN,N (VNN) and VN,NN (VN ) transition (diagonal) potentials between NN,N NNN and NN spaces (A=3), m = M MN We take into account electromagnetic operators with the ( IC) represented by the following graphs

28 LIT equation with degrees of freedom ~ =~ ~ N + ~ ~ = V (TN + VNN ) + ONN 0,N + ON 0, N NN,N ~ + O +O ( m + T + VN ) ~ = VN,NN N 0,N 0, =H VNN,N (VNN) and VN,NN (VN ) transition (diagonal) potentials between NN,N NNN and NN spaces (A=3), (TN+V realistic m = M MN 1 ~ ) N = VNN,N (H ) (O N 0,N + O 0, + ONN 0,N + ON 0,

29 Details for the RT calculation Full consideration of final state interaction via LIT method Nuclear Force model: Argonne V18 two-nucleon potential and Urbana IX three-nucleon force Calculation of bound state wave function and solution of LIT equation with help of expansions in correlated hyperspherical harmonics Consideration of isovector meson exchange currents consistent with AV18 potential Calculation in active nucleon Breit (ANB) frame (PT= Aq/2) and subsequent transformation to laboratory system One-body current operator includes all relativistic corrections up to the order M 3 (leading order M 1) as made for deuteron electrodisintegration (F. Ritz et al, PRC 55, 02214) Multipole expansion of current (maximal jf q dependent, e.g, jf =35/2 for q=700 MeV/c) -currents ( -IC)

30 Results

31 Frame dependence can be cured in a two fragment model Comparison of ANB and LAB calculation: strong shift of peak to lower energies! (8.7, 16.7, 29.3 MeV at q=500, 600, 700 MeV/c)

32 Δ-IC contribution Dotted: without Dashed with

33 Effect of twofragment model Dashed: with (as before) Solid: same but with twofragment model Experimental data: Bates, Saclay, world data (J. Carlson et al.)

34 Deltuva et al. (PRC70, ,2004): Calculation of RT of 3He with CDBonn and CDBonn+ : no effects in peak region!

35 Partial compensation of -IC and 3NF Dotted: no and no 3NF Dashed: no but with 3NF Solid: with and with 3NF No effect in peak region In a CC calculation!

36 Only Isospin channel T=3/2 Dotted: no and no 3NF Dashed: no but with 3NF Solid: with and with 3NF IC contribution larger than 3NF effect in peak region!

37 It is interesting to see what happens at even higher q Presently we are calculating RT in the range from 700 to 1000 MeV/c Here only some preliminary results

38 Preliminary results at higher q example: effect on LIT of sum of magnetic multipoles (T=3/2) Dashed: without -IC Solid: with -IC

39 O+ resonance in longitudinal response function RL in 4He(e,e') with LIT method see also calculations of RL in 4He(e,e') in S. Bacca, N. Barnea, WL, G.Orlandini, PRL 102, and PRC 80, 06401

40 Example: 2H(e,e') 0+ Resonance in the 4He compound system Resonance at ER = -8.2 MeV, i.e. above the 3H-p threshold. Strong evidence in electron scattering off 4He G.G. Simon et al., NPA 324,277 (1979) G. Köbschall et al., NPA 405, 648 (1983)

41 LIT - Inversion Standard LIT inversion method Take the following ansatz for the response function R(ω) (or Ffi(E,E')) M R(ω') = m=1 cm χm(ω', i) with max ω'=ω-ωth, given set of functions χm, and unknown coefficients cm Define: ~ χm(σr,σι, i) = 0 dω' χm(ω', i) (ω'- σr)2 +σι2 ~~,σ ) = < for many σr and fixed σι R Ι Take calculated LIT L(σ ~: and expand in set χ m Determine cm via best fit M L(σR,σΙ) = m=1 cm ~ χm(ω', i) max

42 Increase Mmax up to the point that stable result is obtained for R(ω). Even further increase of Mmax might lead to oscillations in R(ω) As basis set χm we normally use χm(ω', i) = (ω') 1exp(- 2ω'/m)

43 i =0.001 MeV I = MeV

44 i =0.001 MeV I = MeV I = 1 MeV

45 i =0.001 MeV I = MeV I = 5 MeV I = 1 MeV

46 The present precision of the calculation does not allow to resolve the shape of the resonance, therefore the width cannot be determined.

47 The present precision of the calculation does not allow to resolve the shape of the resonance, therefore the width cannot be determined. However, the strength of the resonance can be determined!

48 The present precision of the calculation does not allow to resolve the shape of the resonance, therefore the width cannot be determined. However, the strength of the resonance can be determined! Of course not by taking the strength to the discretized state, but by rearranging the inversion in a suitable way:

49 The present precision of the calculation does not allow to resolve the shape of the resonance, therefore the width cannot be determined. However, the strength of the resonance can be determined! Of course not by taking the strength to the discretized state, but by rearranging the inversion in a suitable way: Reduce strength to the state up to the point that the inversion does not show any resonant structure at the resonance energy ER: R LIT( LIT( ) - fr R / [(ER )2 ] LIT( f R with resonance strength fr R R

50 Determination of resonance strength fr

51 Determination of resonance strength fr Include in the inversion a basis function with resonant structure (E') = 1 1 / [(ER E')2 ] and check inversion result.

52 Determination of resonance strength fr Include in the inversion a basis function with resonant structure (E') = 1 1 / [(ER E')2 ] and check inversion result. Vary LIT( fr by changing fr up to the point that no resonant R structure is present. Then fr corresponds to the resonance strength.

53 fr Inversion results with different fr values AV18+UIX, q=300 MeV/c ( = 0.1 MeV)

54 fr Inversion results with different fr values AV18+UIX, q=300 MeV/c ( = 0.1 MeV) fr

55 Results for the resonance strength and comparison to experimental data In Giuseppina's talk on Friday

56 Density excitation response in bulk atomic 4He at T = 0 with the Sumudu transform (A.Roggero, F. Pederiva, G.Orlandini)

57 MONTE CARLO METHODS ARE APPLIED TO CALCULATE Φ(t)= t, x) (0, 0 ) > d x > e 3 ite S(E) de

58 MONTE CARLO METHODS ARE APPLIED TO CALCULATE Φ(t)= t, x) (0, 0 ) > d x > e 3 Imaginary time τ = it ite S(E) de e τε Laplace kernel

59 MONTE CARLO METHODS ARE APPLIED TO CALCULATE Φ(t)= t, x) (0, 0 ) > d x > e 3 Imaginary time τ = it S(Ε) = Dynamical Structure Function S(E) de e τε Laplace kernel In Condensed Matter Physics: = Density Operator ite In Nuclear Physics: = Charge or current density operator S(Ε) = R(Ε) Response Function In QCD = quark operators S(Ε) = Hadronic Spectral Function

60 A good kernel for Monte Carlo methods: (A.Roggero, F. Pederiva, G.Orlandini 2012) combination of Sumudu kernels: KP(ω, σ) = Ν ( e ν/µ = b/a ν µ = µ ω/σ e ) ν ω/σ P (ln [b] ln [a])/(b-a) b > a >0 integer KP(ω, σ) δ (ω σ) P

61 Density excitation response in bulk atomic 4He at T = 0 Th: Q = 0.4 A-1 T=0 Exp: Q= 0.44 A-1 T=1.35 K1

62 Transform