Planck Mission Reveals Universe Features: String Theory Hits

[Chronos]

The Planck mission has revealed some interesting features of the universe. I will attempt to recap some of the highlights from preprint papers at http://www.sciops.esa.int/index.php?project=PLANCK&page=Planck_Published_Papers .

XV: there is a 5-10% deficit in low mode [l<40] power spectrum vs standard LCDM
XV1 : no evidence for dynamical dark energy models of inflation, adding Ho to CMB and
BAO yields Neff of 3.62. Additional neutrino species are not conclusively
excluded, or preferred.
XVII: inflation models with exponential, monomial or quadratic large field potentials are
disfavored.
XXIX: severe constraints are imposed on enkryptotic/cyclical, gauge field, warm and
k-inflation models.
XXV: no evidence of cosmic strings is detected.
XXVI: Bianci VII models are disfavored. No evidence of vorticity, circles in the sky,
compact topology at sizes < surface of last scattering.

In short, my read is string theory took some big hits here.

 

[Haelfix]

String theory makes very few predictions about inflation or cosmology as I'm sure you know, so what you say is incorrect. Further, none of the statements above have much to do with strengthening or lowering subjective prior beliefs in the theory.

Right now, the data disfavors hybrid inflation, and polynomial inflation with n>2 but favors many of the model building potentials found in a lot of stringy literature (axion based potentials, hill top etc) as well as the usual textbook single field slow roll based models.

There was speculation that if certain stars aligned correctly, that it might be possible to observe a very special type of 'cosmic string' that would indicate something out of string theory. But that was never a necessity either and even if there had been a cosmic string, it wasn't guaranteed that it would be out of string theory.

 

[Chronos]

Agreed, but, the data clearly disfavors ekpryotic/cyclical models of the sort proposed by Steinhardt, which are clearly stringy. It also shows no evidence for cosmic strings, which are also string motivated.

 

[Haelfix]

Cosmic strings are actually not from string theory. They are quite independant constructions. They have to do with special boundary conditions in the early universe associated with phase transitions.

They are very analogous to topological defects in condensed matter, such as domain walls and monopoles.

One of the initial goals of inflation was to explain why we don't see any of these creatures, since they are rather generic in model building. Anyway the inflationary mechanism dilutes their density to effectively unobservable levels unless we happen to get extremely lucky. So its perhaps not too surprising that we don't see any cosmic strings in a universe that seems to favor inflationary dynamics.

Also, The Ekyprotic and cyclic universes have enough parameter space that I doubt we'll hear the last of them. Further, I believe most string theorists view those constructions as baroque and probably inconsistent (this has to do with exotic conditions that seem to violate the usual Horova-Witten constructions)

 

[Chronos]

Planck found no evidence for topological defects in general, which was an important element in disfavoring ekpyrotic/cyclical models [you had me worried there for a minute, thought I may have misspelled ekpyrotic]. I do, however, agree Steinhardt's models are not widely embraced within the string community. In any event, I am by no means an expert on things stringy, I know just enough to get me in over my head.

 

[skydivephil]

As I understand it the ekpyrotic model like the inflation model has more than one verison and the generic difference between the two class of models is in the tensor modes. As Planck has said nothing about these yet, then I doubt the ekyprotic mdoels will go away.
I also spoke to somone who works on the bubble collisions detection project. They said they haven't got a chance to run the data through their alogirthim yet. So whether there are some interesting circles in the sky , remains to be seen. If they do find something that will rule out the ekprotic model without the need for tensor modes. But I am not holding my breath.