# Characteristics of strings

1. Aug 17, 2004

### Glenn

In laymans terms, what characteristic of a string do scientists use to determine the string's mass, spin, and charge?

Are the three known families of particles at all analagous to musical octives?

Can a given string simlutaneously have two different frequencies which are perpendicular to each other? By this I mean that if we could view a string from the side, it would appear as a line. Along that axis could it also be vibrating?

Thanks,
Glenn

2. Aug 17, 2004

### sol2

http://a799.g.akamai.net/3/799/388/3d94d6b574ec9f/www.msnbc.com/news/wld/graphics/superstring.gif is for you Glenn

Last edited by a moderator: Apr 21, 2017
3. Aug 18, 2004

### Glenn

Sol2,
Thanks for the link, however it doesn't work. It appears to be a GIF file on which I am unable to click the "Next" button.

Please repost the link if you have it available.

Thanks,
Glenn

4. Aug 18, 2004

### Glenn

5. Aug 18, 2004

### Glenn

Hmmmmmmm....... that didn't tell me quite what I wanted to know.

Anyone have a more specific answer or perhaps another link?

Thanks,
Glenn

6. Aug 18, 2004

Staff Emeritus
The basic parameter that controls string physics is tension. The string doesn't have mass itself, but can generate massive particles by its vibration, the higher the frequency of the vibration the higher the mass. But the massive string particles are not seen. Rather string phenomenology relies on low frequency massless particles which acquire mass in other ways at low energies (e.g. Higgs mechanism). Charge is imposed on the worldsheet or the branes as a separate step. Spin, or helicity, can be generated from multiple branes. Getting the correct chiral behavior of the standard model is something string physicists pay a lot of attention to. All the more important in that chirality in the SM is still generating new physics (neutrino mass, CP violation).

Not in the Pythagorean vibration -> musical tone sense. The "flavors" as the three generations are now called are a feature of the group structure of the SM, specifically the interaction of the part that generates electroweak behavior and the part that does the strong force. Some intersecting brane models can reproduce this physics.

Another way to generate flavors has been suggested, a topological one. The higher dimensions of string physics are often thought of as compacted on tiny six dimensional shapes such as Calabi-Yau manifolds or higher tori. These may not be simply connected, meaning they have "handles" around which a string could loop, one, two, or more times. Then it is thought by some if two strings vibrate with different wrapping numbers it could generate particle families of different mass. This is certainly an attractive idea, but see my comments on particle mass above.

Yes. a string can support complex vibrations which can be analyzed into an infinite set of normal modes - just like a violin string. The vibrations happen in the transverse dimensions, the ones not entrained by the two dimensional world sheet. In ten dimensional superstring theories there are 8 dimensions to vibrate in. Each normal mode can generate a particle, so multiple particles can come out of one string. In the case of closed string you also have left moving and right moving excitations which interact, forming particles. The graviton is one particle formed this way.

Last edited: Aug 18, 2004
7. Aug 18, 2004

### Glenn

Thank you for the in depth reply!

-Glenn