Recent content by bapowell

Suppose you want the largest-scale modes (##k## corresponding to the CMB quadrupole) to be exiting the horizon at ##N=60##. To initialize these largest-scale modes, go back in time until you are "close" to the BD limit, say, when ##k = 100aH##. The corresponding value of ##N## should be your...

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Yes, if you fit a LCDM+tensors model to the CMB T/E spectra, you might eventually get an r > 0 at some level of confidence. But that's not what it means to detect tensors, since I can always fit a plain old LCDM model to the same data and get a good fit as well. You ultimately need to do some...

Each of the alternatives I listed can generate tensors. Now, whether they do, as with inflation, is totally unknown and depends on things like the energy scale of the epoch. I doubt this. I'll bet that for a given T/E spectrum from an inflation model w/ tensors, I can give you at least one...

Energy scales that increase in time would also generate a blue tensor spectrum. A red tensor spectrum is a "smoking gun" signature of inflation that, though very difficult to detect, would be a strong discriminator between inflation, bounces models, and string gases.

I'm not sure...not an expert. Just a curious bystander. My limited impression is that in some of these instances, there simply is no corresponding dS solution in the UV-complete theory.

This thread (a few below this one) has been going for some time now: https://www.physicsforums.com/threads/no-metastable-type-iib-de-sitter-vacua.950271/

Depends. First- or second-order transition? If the latter, then there is a direct connection between the shape of the potential, i.e. the dynamics of the phase transition, and the characteristics of the density perturbations.

If correct, they once again make string theory inhospitable to inflation. Mathematical proofs can’t rule out inflation, which is a model based on effective theories to describe observable phenomena.

Thanks Urs. Any chance you can summarize what the assumption was?

The OP is referring to "homomorphism", not "homeomorphism".

If that’s your definition, there is certainly a mechanism: a supercooled uniform scalar field fuels exponential expansion until it decays to a true vacuum. The latent heat of the phase transition repopulates the universe with matter. What’s missing? Compared to your example of GR, it’s rather...

Yeah, that's not accurate. That was the original hope (nearly 40 years ago now) that the GUT phase transition was trapped in a metastable false vacuum, triggering inflation. That would have been a beautiful marriage of particle physics and cosmology, aligning definitive events in each arena...

How do you define "mechanism"? Early attempts at inflation centered on presumed phase transitions, typically of the GUT variety, that are expected to have taken place in the early universe. The mechanism in which a scalar field becomes trapped in a false vacuum as the temperature drops below...

Which claim? Off the top of my head, the only SM field that is still an inflaton candidate is the Higgs, but only with an arguably ad hoc and fine-tuned nonminimal coupling to curvature. To me, that's less attractive than a new field that might happen to work more naturally. A similar thing...