Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

String theory and fundamental physical constants

  1. Nov 21, 2015 #1

    ftr

    User Avatar

    I have heard that ST can calculate the masses of the particles species of some vacuum and also its decay rate, charge and so on, but I have not seen any clear paper on the subject. Can anyone point me to one?

    Are "hbar" and "c" the same in all the vacuums?why or why not?

    Can ST predict the existence of a particle that is a composition like proton?
     
  2. jcsd
  3. Nov 22, 2015 #2
  4. Nov 23, 2015 #3

    Demystifier

    User Avatar
    Science Advisor

    Physicists also claim that, in principle, from Schrodinger equation one can calculate the properties of the DNA molecule, and yet you will never find a clear paper on the subject. If you can answer why is that the case, I can tell you that a similar answer can be applied to your question.
     
  5. Nov 23, 2015 #4

    ftr

    User Avatar

    Thanks I know about that one, but I wanted something more specific.


    If you ask some experts they always get defensive. I was actually hoping for Mitchell Porter to jump in since he said this in another post

    "Being wrapped around one hole in the CY is physically different from being wrapped around another hole in the CY, and it means that the string will be interacting differently with the geometric moduli defining the size and shape of the CY. In such a model, this is what gives the particles their different masses. But because CY dynamics is so difficult to calculate, people have mostly settled for getting other properties right, like the low-energy symmetries - some part of the E8 x E8 symmetry that still survives even after compactification."
     
  6. Nov 23, 2015 #5

    haushofer

    User Avatar
    Science Advisor

    That's not being defensive, but reality. It's like calculating phasetransitions using the Standard Model: the difference in energy scales is huge.
     
  7. Nov 23, 2015 #6

    ftr

    User Avatar

    I am not sure if I am getting you. ST claims to "find" particles after compactification, so what is it that is being found about them.
     
  8. Nov 24, 2015 #7

    Demystifier

    User Avatar
    Science Advisor

    The problem is to make the compactification. There are at least ##10^{500}## different ways to do that, so in practice it is too difficult to find out which compactification is the "right" one, i.e. which compactification describes the particles we see.
     
  9. Nov 24, 2015 #8
    I have not found papers that satisfy me as a response to your question, but I will exhibit two examples focusing on the mass of Standard Model fermions, which comes from yukawa couplings to the Higgs field. To predict the masses would mean to predict the yukawa coefficients, and the vacuum expectation value of the Higgs field.

    This 2002 paper describes "intersecting braneworlds". The fermions are strings at the intersection of branes, the Higgs is a string between two parallel branes, the yukawa interaction involves contact between those strings, and the strength of the interaction depends on the area of the surface they trace out in order to come into contact, see figure 1 and equation 3.1. The paper specifies a particular brane geometry that gives the gauge fields and particle generations of the standard model, and then asks if the exact spacing and angles of the branes can be chosen so as to give the observed values of the SM parameters. The authors say yes, see various tables in part 4.

    But that still leaves open the question whether any of those exact brane configurations are stable. Or would the branes move away from those positions, spoiling the quantitative match? Here see the second paragraph on page 26: the authors hope that one of these configurations might be produced as a stable perturbation of a dynamically favored symmetrical configuration.

    I believe this paper turned out to be flawed (see the disclaimer added to the abstract), but I chose it because it's easy to point out where and how they try to match reality.

    The other paper comes from 2013 and I chose it because I think it's considered an important paper within a major school of thought, that it's still the state-of-the-art way within "F-theory" to give the top quark its large mass. Here they speak of yukawa couplings arising from "wavefunction overlap" but otherwise it's similar, the fermions and the Higgs are localized near each other in the extra dimensions... The calculations occur in part 6 and again, the algebra is followed by an attempt (6.14) to identify plausible specific values for properties of the compactification that will give an empirically correct outcome (6.15).

    I'll also mention Kaplunovsky & Louis 1995 as an example of a theory paper that's not about a particular model, but rather, about the general form of the relationship between couplings in a field theory, and parameters coming from a deeper theory like string theory.
     
  10. Nov 24, 2015 #9

    ftr

    User Avatar

    Thanks Mitchell, much appreciated. I have some reading to do before I respond. Meanwhile is it possible to shed some light on my other questions( if not too much trouble of course), hopefully that will give me a better perspective on the issue. Thanks again.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: String theory and fundamental physical constants
Loading...