# SM particles in highly curved spacetime

1. Sep 6, 2009

### ensabah6

I'm curious as to whether parameters like rest mass and mixing angles, half-life for 2nd/3rd gen and other properties change for SM particles like muons in highly curved spacetimes.

2. Sep 7, 2009

### hamster143

Local parameters, rest mass, half-life, etc. are the same. No matter how curved your spacetime is, there's a locally inertial frame of reference that looks like flat spacetime.

Anything that involves propagation, results in seriously screwy and complicated dynamics. You get pair production, red shift / blue shift, etc. There's even a basic theorem demonstrating that vacuum in one reference frame is no longer the vacuum in a different reference frame that's accelerated with respect to the first one (Unruh effect). Meaning that, if you have two observers passing through the same area of curved spacetime on different trajectories (e.g. one suspended above a gravitating object by constantly firing engines, and the other in free fall towards the object), one of them might see vacuum and the other might see a soup of particles.

3. Sep 11, 2009

### Haelfix

Its also somewhat illdefined as well. One of the axioms of field theory is that the fourier modes should asymptotically die off far from the source of the field disturbance/excitation. That way we have a sensible measure for free particles (the one thing we really understand well mathematically).

In curved spacetime, that is no longer necessarily the case. Sometimes you have modes that blow up, and sometimes even go into transplanckian regimes (where presumably quantum gravity plays a role) and we don't know how to deal with that. There might be backreactions onto the metric, and our approximation could break down.

So the whole subject of fields in curved spacetime is a sort of formal manipulation of quantities that kind of works so long as the metric doesn't get too curvy and the properties are nice enough that we can do something with it. One must keep in mind that it only works in certain regimes, and that its far from being rigorous mathematically (even for a physicist).

One of the upshots is (as Hamster points out) that particles lose their invariant meaning globally. Instead more formal operators and functions take center stage. It really requires a specialized textbook treatment to understand (and be warned, its complicated material).

4. Sep 11, 2009

### ensabah6

HAelfix & hamter, thanks.

What about curved spacetimes that change rapidly as well?

Is there any way to match predictions with say cosmic rays near black holes or neutron stars or big bang nucelosynthesis?