TY  - JOUR
PB  - SciPost Foundation
DO  - 10.21468/SciPostPhys.18.6.179
TI  - Lightcone Hamiltonian for Ising field theory I: $T < T_c$
PY  - 2025/06/05
UR  - https://scipost.org/SciPostPhys.18.6.179
JF  - SciPost Physics
JA  - SciPost Phys.
VL  - 18
IS  - 6
SP  - 179
A1  - Fitzpatrick, Andrew Liam
AU  - Katz, Emanuel
AU  - Xin, Yuan
AB  - We study 2d Ising Field Theory (IFT) in the low-temperature phase in lightcone quantization, and show that integrating out zero modes generates a very compact form for the effective lightcone interaction that depends on the finite volume vacuum expectation value of the $\sigma$ operator. This form is most naturally understood in a conformal basis for the lightcone Hilbert space. We further verify that this simple form reproduces to high accuracy results for the spectra, the $c$-function, and the form-factors from integrability methods for the magnetic deformation of IFT. For generic non-integrable values of parameters we also compute the above observables and compare our numeric results to those of equal-time truncation. In particular, we report on new measurements of various bound-state form-factors as well as the stress-tensor spectral density. We find that the stress tensor spectral density provides additional evidence that certain resonances of IFT are surprisingly narrow, even at generic strong coupling. Explicit example code for constructing the effective Hamiltonian is included in an appendix.
ER  -

@Article{10.21468/SciPostPhys.18.6.179,
	title={{Lightcone Hamiltonian for Ising field theory I: $T < T_c$}},
	author={Andrew Liam Fitzpatrick and Emanuel Katz and Yuan Xin},
	journal={SciPost Phys.},
	volume={18},
	pages={179},
	year={2025},
	publisher={SciPost},
	doi={10.21468/SciPostPhys.18.6.179},
	url={https://scipost.org/10.21468/SciPostPhys.18.6.179},
}