# Truncated Hilbert Space Approach for the 1+1D phi^4 Theory

- Institution: CERN
- Department: TH String Theory Seminar
- Speaker: Marton Lájer
- Year: 2016
- Language: English
- Subjects: Astronomy and space
- Source: [CERN](https://videos.cern.ch/record/3002967)
- Licence: [CERN](http://copyright.web.cern.ch)
- Who can watch: Tweens profiles and older (sources give no ratings; placed by Invisible Network from the source's own words)

(an informal seminar, not a regular string seminar) We used the massive analogue of the truncated conformal space approach to study the broken phase of the 1+1 dimensional scalar phi^4 model in finite volume, similarly to the work by S. Rychkov and L. Vitale. In our work, the finite size spectrum was determined numerically using an effective eigensolver routine, which was followed by a simple extrapolation in the cutoff energy. We analyzed both the periodic and antiperiodic sectors. The results were compared with semiclassical and Bethe-Yang results as well as perturbation theory. We obtained the coupling dependence of the infinite volume breather and kink masses for moderate couplings. The results fit well with semiclassics and perturbative estimations, and confirm the conjecture of Mussardo that at most two neutral excitations can exist in the spectrum. We believe that improving our method with the renormalization procedure of Rychkov et al. enables to measure further interesting quantities such as decay rates and the inelastic part of scattering matrices. .

0:00:00 Slide 1

0:00:34 Slide 2

0:01:35 Slide 3

0:03:34 Slide 4

0:04:02 Slide 5

0:04:07 Slide 6

0:04:31 Slide 7

0:05:01 Slide 8

0:06:55 Slide 9

0:08:29 Slide 10

0:08:34 Slide 11

0:09:59 Slide 12

0:11:27 Slide 13

0:11:47 Slide 14

0:14:14 Slide 15

0:15:12 Slide 16

0:15:26 Slide 17

0:18:45 Slide 18

0:20:02 Slide 19

0:21:05 Slide 20

0:21:56 Slide 21

0:22:00 Slide 22

0:23:13 Slide 23

0:24:09 Slide 24

0:25:09 Slide 25

0:25:20 Slide 26

0:26:49 Slide 27

0:27:40 Slide 28

0:27:55 Slide 29

0:28:50 Slide 30

0:29:15 Slide 31

0:30:58 Slide 32

0:31:41 Slide 33

0:32:04 Slide 34

0:33:36 Slide 35

0:34:33 Slide 36

0:34:56 Slide 37

0:35:11 Slide 38

0:36:57 Slide 39

0:37:29 Slide 40

0:37:38 Slide 41

0:39:13 Slide 42

0:40:34 Slide 43

0:40:38 Slide 44

0:42:45 Slide 45

0:44:09 Slide 46

0:44:30 Slide 47

0:46:15 Slide 48

0:47:01 Slide 49

0:47:33 Slide 50

0:47:51 Slide 51

0:49:32…

## Lectures

1. [Truncated Hilbert Space Approach for the 1+1D phi^4 Theory](https://invisiblenetwork.ai/learn/cern/3002967/1fe22e991853), 1 h 5 min (CERN's player)