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PhD thesis in English

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2. Diagonalization of Transition Amplitudessame order if one uses sufficiently f<strong>in</strong>e discretization (∆ = 0.05). Therefore, thesaturation of errors on the left-hand graph are caused by the errors due to the timeof propagation. However, if one uses discretization which is not sufficiently f<strong>in</strong>e, thesaturation of errors can be also caused by the discretization effects. Such effects can|| E 0(p) (∆, L, t) - E 0exact10 -2 110 -410 -610 -810 -1010 -1210 -1410 -1610 -1810 -20p = 1p = 3p = 5p = 7p = 9p = 11p = 131 1.5 2 2.5 3 3.5L10 5 0.001 0.01 0.1|| E 0(p) (∆, L, t) - E 0exact10 -5 110 -1010 -1510 -20∆ = 0.05∆ = 0.10∆ = 0.2010 -25Figure 2.9: Deviations from the ground energy |E (p)0 (∆, L, t) − Eexact 0 | as a functionof the space cutoff L (top) and as a function of the time t (bottom). The groundenergy is obta<strong>in</strong>ed us<strong>in</strong>g different levels p = 1, 3, 5, 7, 9, 11, 13 (top to bottom) ofthe effective action for the quartic anharmonic potential, with parameters k 2 = 1,k 4 = 48, ∆ = 0.05, t = 0.02 on top graph, and L = 4 on bottom graph. Theexact ground energy E0 exact = 0.95156847272950001114693 . .. is taken from Ref. [61].Dashed l<strong>in</strong>es on the graph (b) correspond to the discretization error (2.19).t39

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