What Are P-Branes and Their Role in String Theory?

[alexsok]

Earlier today, i had a coup doeil through the following article:
http://cerncourier.com/main/article/43/6/15/1

While most of it was clear as sun, certain issue did arise, and i'd like you guys to crystalise those to me.

A crucial role in these developments was played by the discovery of "p-branes", which are higher dimensional objects extended in p spatial dimensions, so generalizing the notion of a point particle (p = 0) or a string (p = 1). One of the main consequences of this discovery is that the string scale is, in general, a free parameter that can be dissociated from the Planck mass if the universe is localized on a p-brane and does not feel all the extra dimensions of string theory. The braneworld description of our universe separates the dimensions of space into two groups: those that extend along our p-braneworld, called parallel dimensions, and those transverse to it. Obviously the parallel ones must contain at least the three known dimensions of space, but they may contain more.

I've been told by emeritus in particle physics, the following:

d-branes float in subspace orthogonal to 'our' classical 3 dimensions space. the direct sum of the classical 3-dimensions space with d-brane spaces give the p-brane space

So my first question is conspicuously carnassial: does this definition hold true for all cases, or it could manifest itself elsewhere? Is it even correct to define the p-brane space in such a way?

My second question is more of a request for a better explanation and requires the following figure.

In the type I string framework, our universe contains (besides the three known spatial dimensions; denoted by a single blue line) some extra dimensions (dII = p-3) parallel to our world p-brane (green plane), along which the light described by open strings propagates, as well as some transverse dimensions (yellow space), where only gravity described by closed strings can propagate. The longitudinal extra dimensions have a string size of about 10-18 m, while the size of the transverse dimensions varies between 10-14 m and a fraction of a millimetre.

Could anyone here put it in a more familiar language?

Thanks guys.

 

[R0man]

Thank you for sharing your thoughts on exploring p-branes. It seems like you have a good understanding of the concept and its implications in string theory. To address your first question, the definition of p-branes as higher dimensional objects extended in p spatial dimensions is generally correct. However, there are different types of p-branes, such as D-branes, NS-branes, and M-branes, which have different properties and dimensions. So while the general concept of a p-brane is true for all cases, the specific dimensions and properties may vary depending on the type of p-brane.

As for your second question, the figure you have shared is a visualization of the braneworld scenario in type I string theory. It shows our universe (the blue line) as a p-brane with three known spatial dimensions, surrounded by extra dimensions (yellow space) where gravity can propagate through closed strings. The parallel dimensions (green plane) are where open strings can propagate and are responsible for the other forces in our universe. The size of these extra dimensions can vary, with the longitudinal dimensions being much smaller than the transverse dimensions. In simpler terms, the figure is showing how our universe exists within a larger dimensional space, and the different types of strings that can propagate in each dimension.

I hope this helps clarify some of your doubts about p-branes. Keep exploring and learning about this fascinating concept in string theory!