Inflation and GUTs: Energy Scales & Model Dependence

[Jim]

Can someone please clarify if the energy scales of Inflation & GUTs are identical,
or model-dependent ? One typically sees ~10^15 Gev to 2x10^16 Gev in the literature,
which is a small variance, but its not clear if there are `standard values'.

I am also curious if one can have inflation without GUTs ?

 

[javierR]

The scales of inflation and GUTs are independent, so yes, one can have inflation without GUTs. And on the flip side, GUTs don't automatically incorporate inflation. The usually quoted characteristic energy scale of inflation 10^15-10^16 Gev is based on observation. Unlike inflation, GUTs are hypothetical, and the energy scales associated with them are model-dependent. It just so happens that "standard" field theory GUTs require a scale of 10^16 Gev. But there are certainly GUTs, e.g. in theories with at least one extra dimension, in which the characteristic scale is of a different order of magnitude.

 

[Haelfix]

Keep in mind, historically, inflation was partially invented to rescue GUT theories in cosmology. GUT theories are amongst the most widely held beliefs (that we can't prove) in the HEP community. They're almost taken for granted.

The problem is many typical models incorporate a preponderous of particles like magnetic monopoles and other various topological defects. Roughly, they should be everywhere, b/c the big bang would copiously produce them and that is flagrantly in violation of observation.

Enter an inflationary epoch somewhere around the GUT scale (typically a little bit higher energy), which dilutes the abundance to observational limits.

 

[friend]

I am also curious if one can have inflation without GUTs ?

Just a thought, particles are created near horizons, e.g. black holes. But acceleration also creates horizons, i.e. Unruh effect. So if space is expanding exponentially (inflation), then every point in space becomes an horizon due to acceleration. So perhaps it is that inflation is what is responsible for the original particles to begin with, and therefore connected in some way to GUT's

 

[Jim]

Thanx all for your quik responses !

Haelfix: Agree about the historical correlation. Running with the mSSM value of 2E16 Gev
for the GUT group to split into SU(3) and SU(2)xU(1), this occurs considerably prior to reheating at ~ 2E15 Gev, when FRW evolution kicks in again. The time scales are approx.,
Trh ~ 100Tgut. Clearly, there is a temporal sequence of events here.

In terms of chicken v. egg, accd'g to Guth, inflation began ~ 10^-37 sec. mSSM GUT energy corresponds to a time scale of about 10^-39 sec, which strongly suggests a causal relation, with the GUT symmetry breaking causing the phase transition driving inflation.
Indeed, it seems more aesthetic to have the GUT symmetry breaking initiate inflation, since GUTs correspond to ~ 100-1000 Planck lengths, whereas inflation ranges up into the macroscopic domain ~ centimeters.