# CMB hemispherical asymmetry from non-linear isocurvature perturbations

## Abstract

We investigate whether non-adiabatic perturbations from inflation could produce an asymmetric distribution of temperature anisotropies on large angular scales in the cosmic microwave background (CMB). We use a generalised non-linear δ N formalism to calculate the non-Gaussianity of the primordial density and isocurvature perturbations due to the presence of non-adiabatic, but approximately scale-invariant field fluctuations during multi-field inflation. This local-type non-Gaussianity leads to a correlation between very long wavelength inhomogeneities, larger than our observable horizon, and smaller scale fluctuations in the radiation and matter density. Matter isocurvature perturbations contribute primarily to low CMB multipoles and hence can lead to a hemispherical asymmetry on large angular scales, with negligible asymmetry on smaller scales. In curvaton models, where the matter isocurvature perturbation is partly correlated with the primordial density perturbation, we are unable to obtain a significant asymmetry on large angular scales while respecting current observational constraints on the observed quadrupole. However in the axion model, where the matter isocurvature and primordial density perturbations are uncorrelated, we find it may be possible to obtain a significant asymmetry due to isocurvature modes on large angular scales. Such an isocurvature origin for the hemispherical asymmetry would naturally give rise to a distinctive asymmetry in themore »

- Authors:

- Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Burnaby Road, Portsmouth PO1 3FX (United Kingdom)
- School of Astronomy, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of)
- Department of Physics, The University of Texas at Dallas, Richardson, TX 75083 (United States)

- Publication Date:

- OSTI Identifier:
- 22525896

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2015; Journal Issue: 04; Other Information: Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANISOTROPY; ASYMMETRY; CORRELATIONS; COSMOLOGICAL INFLATION; DENSITY; DISTURBANCES; FLUCTUATIONS; LIMITING VALUES; MULTIPOLES; NONLINEAR PROBLEMS; POLARIZATION; RELICT RADIATION; SCALE INVARIANCE

### Citation Formats

```
Assadullahi, Hooshyar, Wands, David, Firouzjahi, Hassan, and Namjoo, Mohammad Hossein, E-mail: hooshyar.assadullahi@port.ac.uk, E-mail: firouz@mail.ipm.ir, E-mail: mohammadhossein.namjoo@utdallas.edu, E-mail: david.wands@port.ac.uk.
```*CMB hemispherical asymmetry from non-linear isocurvature perturbations*. United States: N. p., 2015.
Web. doi:10.1088/1475-7516/2015/04/017.

```
Assadullahi, Hooshyar, Wands, David, Firouzjahi, Hassan, & Namjoo, Mohammad Hossein, E-mail: hooshyar.assadullahi@port.ac.uk, E-mail: firouz@mail.ipm.ir, E-mail: mohammadhossein.namjoo@utdallas.edu, E-mail: david.wands@port.ac.uk.
```*CMB hemispherical asymmetry from non-linear isocurvature perturbations*. United States. doi:10.1088/1475-7516/2015/04/017.

```
Assadullahi, Hooshyar, Wands, David, Firouzjahi, Hassan, and Namjoo, Mohammad Hossein, E-mail: hooshyar.assadullahi@port.ac.uk, E-mail: firouz@mail.ipm.ir, E-mail: mohammadhossein.namjoo@utdallas.edu, E-mail: david.wands@port.ac.uk. Wed .
"CMB hemispherical asymmetry from non-linear isocurvature perturbations". United States.
doi:10.1088/1475-7516/2015/04/017.
```

```
@article{osti_22525896,
```

title = {CMB hemispherical asymmetry from non-linear isocurvature perturbations},

author = {Assadullahi, Hooshyar and Wands, David and Firouzjahi, Hassan and Namjoo, Mohammad Hossein, E-mail: hooshyar.assadullahi@port.ac.uk, E-mail: firouz@mail.ipm.ir, E-mail: mohammadhossein.namjoo@utdallas.edu, E-mail: david.wands@port.ac.uk},

abstractNote = {We investigate whether non-adiabatic perturbations from inflation could produce an asymmetric distribution of temperature anisotropies on large angular scales in the cosmic microwave background (CMB). We use a generalised non-linear δ N formalism to calculate the non-Gaussianity of the primordial density and isocurvature perturbations due to the presence of non-adiabatic, but approximately scale-invariant field fluctuations during multi-field inflation. This local-type non-Gaussianity leads to a correlation between very long wavelength inhomogeneities, larger than our observable horizon, and smaller scale fluctuations in the radiation and matter density. Matter isocurvature perturbations contribute primarily to low CMB multipoles and hence can lead to a hemispherical asymmetry on large angular scales, with negligible asymmetry on smaller scales. In curvaton models, where the matter isocurvature perturbation is partly correlated with the primordial density perturbation, we are unable to obtain a significant asymmetry on large angular scales while respecting current observational constraints on the observed quadrupole. However in the axion model, where the matter isocurvature and primordial density perturbations are uncorrelated, we find it may be possible to obtain a significant asymmetry due to isocurvature modes on large angular scales. Such an isocurvature origin for the hemispherical asymmetry would naturally give rise to a distinctive asymmetry in the CMB polarisation on large scales.},

doi = {10.1088/1475-7516/2015/04/017},

journal = {Journal of Cosmology and Astroparticle Physics},

number = 04,

volume = 2015,

place = {United States},

year = {Wed Apr 01 00:00:00 EDT 2015},

month = {Wed Apr 01 00:00:00 EDT 2015}

}