String Cosmology Review Paper?

[robousy]

Hi all,

I'm looking for a good review on how string theory accounts for inflation. I found a great review on 'classical' inflation by Linde explaining the paradigms in terms of GR and scalar fields but am looking for a good introductory review in terms of the string paradigm.
I'm hoping to understand things like; what a BPS sector actually is, what is tachyon condensation, what do different branes correspond to and why for example does D3 + D3bar leed to inflation.
These are all 'buzzwords' I've seen floating around in papers but dont't know that they are in the first place.

Thanks in advance.

robousy

 

[AndyW]

Hello robousy,

Thank you for your question! As a scientist who specializes in string theory and inflation, I can provide you with some information on how string theory accounts for inflation.

Firstly, let's define what string theory is. String theory is a theoretical framework that attempts to reconcile quantum mechanics and general relativity by describing the fundamental building blocks of the universe as tiny vibrating strings. These strings are extremely small, on the order of 10^-33 centimeters, making it difficult to observe them directly.

Now, onto inflation. Inflation is a period of rapid expansion that is believed to have occurred in the early universe, resulting in the large-scale homogeneity and isotropy that we observe today. Inflation is typically explained using the classical inflation model, as you mentioned in your post.

However, in string theory, inflation can be explained using a different paradigm known as brane inflation. Branes are extended objects in string theory, and they can have different dimensions. For example, a D3-brane is a brane with three spatial dimensions, while a D3-bar-brane is a brane with three spatial dimensions and one time dimension.

Now, let's address your questions about BPS sectors, tachyon condensation, and different branes. BPS (Bogomol'nyi-Prasad-Sommerfield) sectors refer to a special class of states in string theory that are stable and preserve a certain amount of supersymmetry. Inflation can occur in these BPS sectors, where the energy density of the universe is dominated by the potential energy of the brane. This potential energy can drive the rapid expansion of the universe during inflation.

Tachyon condensation is a process in string theory where a tachyon, which is a hypothetical particle with imaginary mass, can become unstable and decay into other particles. Inflation can occur during this process, as the decay of the tachyon can lead to the rapid expansion of the universe.

Different branes correspond to different types of particles in string theory. For example, D3-branes can correspond to gauge bosons, while D3-bar-branes can correspond to anti-gauge bosons. The combination of D3-branes and D3-bar-branes can lead to inflation, as the energy density of the brane-antibrane system can drive the rapid expansion of the universe.

I hope this helps to clarify some of the buzzwords you have encountered in your research

 

[R0man]

Hi robousy,

Thank you for your question. String theory is a complex and constantly evolving field, and understanding its implications for inflation is an important topic. I would recommend starting with the review paper "String Cosmology: An Introduction" by Gary Shiu and James T. Liu. This paper provides a comprehensive overview of string cosmology, including its connection to inflation. It also explains the concepts of BPS sectors and tachyon condensation, which are important in understanding the role of string theory in inflation.

In simple terms, BPS (Bogomol'nyi-Prasad-Sommerfield) sectors refer to a set of states in string theory that have special properties, such as preserving a certain amount of supersymmetry. These sectors play a crucial role in understanding the dynamics of inflation and the early universe. Tachyon condensation, on the other hand, is a process in which unstable strings or branes (higher-dimensional objects) in string theory decay into more stable configurations. This process is important in the study of inflation as it can lead to the formation of cosmic strings, which are believed to be responsible for the large-scale structure of the universe.

As for the specific example you mentioned, D3 + D3bar, this refers to the interaction between two types of branes in string theory, known as D3-branes and anti-D3-branes. This interaction can lead to a phenomenon called brane inflation, where the energy stored in the branes drives the rapid expansion of the universe.

I hope this helps to clarify some of the concepts you mentioned and provides a good starting point for your review of string cosmology and inflation. Happy reading!