# Squeezed bispectrum in the δ N formalism: local observer effect in field space

## Abstract

The prospects of future galaxy surveys for non-Gaussianity measurements call for the development of robust techniques for computing the bispectrum of primordial cosmological perturbations. In this paper, we propose a novel approach to the calculation of the squeezed bispectrum in multiple-field inflation. With use of the δ N formalism, our framework sheds new light on the recently pointed out difference between the squeezed bispectrum for global observers and that for local observers, while allowing one to calculate both. For local observers in particular, the squeezed bispectrum is found to vanish in single-field inflation. Furthermore, our framework allows one to go beyond the near-equilateral ('small hierarchy') limit, and to automatically include intrinsic non-Gaussianities that do not need to be calculated separately. The explicit computational programme of our method is given and illustrated with a few examples.

- Authors:

- Kavli Institute for the Physics and Mathematics of the Universe (WPI), UTIAS, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583 (Japan)
- Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Burnaby Road, Portsmouth, PO1 3FX (United Kingdom)

- Publication Date:

- OSTI Identifier:
- 22680032

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 02; Other Information: Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; DISTURBANCES; GALAXIES; INFLATIONARY UNIVERSE; PERTURBATION THEORY; SPACE; VISIBLE RADIATION

### Citation Formats

```
Tada, Yuichiro, and Vennin, Vincent, E-mail: yuichiro.tada@ipmu.jp, E-mail: vincent.vennin@port.ac.uk.
```*Squeezed bispectrum in the δ N formalism: local observer effect in field space*. United States: N. p., 2017.
Web. doi:10.1088/1475-7516/2017/02/021.

```
Tada, Yuichiro, & Vennin, Vincent, E-mail: yuichiro.tada@ipmu.jp, E-mail: vincent.vennin@port.ac.uk.
```*Squeezed bispectrum in the δ N formalism: local observer effect in field space*. United States. doi:10.1088/1475-7516/2017/02/021.

```
Tada, Yuichiro, and Vennin, Vincent, E-mail: yuichiro.tada@ipmu.jp, E-mail: vincent.vennin@port.ac.uk. Wed .
"Squeezed bispectrum in the δ N formalism: local observer effect in field space". United States.
doi:10.1088/1475-7516/2017/02/021.
```

```
@article{osti_22680032,
```

title = {Squeezed bispectrum in the δ N formalism: local observer effect in field space},

author = {Tada, Yuichiro and Vennin, Vincent, E-mail: yuichiro.tada@ipmu.jp, E-mail: vincent.vennin@port.ac.uk},

abstractNote = {The prospects of future galaxy surveys for non-Gaussianity measurements call for the development of robust techniques for computing the bispectrum of primordial cosmological perturbations. In this paper, we propose a novel approach to the calculation of the squeezed bispectrum in multiple-field inflation. With use of the δ N formalism, our framework sheds new light on the recently pointed out difference between the squeezed bispectrum for global observers and that for local observers, while allowing one to calculate both. For local observers in particular, the squeezed bispectrum is found to vanish in single-field inflation. Furthermore, our framework allows one to go beyond the near-equilateral ('small hierarchy') limit, and to automatically include intrinsic non-Gaussianities that do not need to be calculated separately. The explicit computational programme of our method is given and illustrated with a few examples.},

doi = {10.1088/1475-7516/2017/02/021},

journal = {Journal of Cosmology and Astroparticle Physics},

number = 02,

volume = 2017,

place = {United States},

year = {Wed Feb 01 00:00:00 EST 2017},

month = {Wed Feb 01 00:00:00 EST 2017}

}