# 9 large dimensions, No curled up ones?

1. Nov 21, 2008

### KeithClemens

Any models worth checking out that do not rely on small curled up dimensions? And by large dimensions I don't mean 1mm, I mean all dimensions equally large.

2. Nov 21, 2008

### robousy

Not that I know of. Even large (mm size) extra dimensions is kind of pushing it in the context of replacing one heirachy with another. You see, if the extra dimensions are large then we are immediately faced with phenomenological issues, i.e. where are they???

There are ways to 'hide' large extra dimensions. Sean Carroll came up with an interesting twist recently. http://arxiv.org/abs/0802.0521

The idea is to inject some generic field with a vev into the 5th dimension into a model.

In KK theory the momentum required to probe the extra dims is on the order of:

$$k\propto\frac{1}{r}$$

However, the existence of this lorentz violating field modifies the dispersion relations of say some scalar field and the momentum now reads:

$$k\propto\frac{(1+\alpha_\phi^2)}{r}$$

where $$\alpha_\phi$$ is the ratio of the vev of the field to its coupling parameter.