Doesn't matter, they are related by a canonical transformation. Depending on the situation you use one or another: for canonical quantization one uses Hamiltonian formalism, for path integrals -- Lagrangian.
No, beacon is right -- there are no power divergencies in the dimensional regularization with mass-independent subtraction like MSbar. That's why it's used in effective field theory calculations (chrial PT, etc), as it does not spoil power counting by introducing unwanted mass scales.
The...
Sure. Well, it's stil gonna be a bit handwaving. First, let's compute the rate for the eak decauy of top quark (t -> b W). The width would come out to be approximately 2 GeV:
\Gamma_t \sim \frac{G_F}{\sqrt{2}} \frac{m_t^3}{8 \pi} \sim 2 ~GeV
This implies that the lifetime is
\tau \sim...
Toponium (top-antitop meson) is not observable because top is too heavy to form a bound state. Simplistically speaking, top quark would decay faster via weak interaction than the time needed for "top-antitop system to make one revolution around each other" (note quotes), i.e. boundstate...
In principle, one can avoid anomaly cancellation requirement if 4th generation quarks are not like the ones from the previous three generations (for example, with vector-type couplings, not chiral)...
but it looks ugly to me, even though some people like it.
Of course, 4th generation...
There are infinities in both types of theoreis. However, there is a finite number of them in renormalizable theories and infinite number -- in nonrenormalizable. The trick with predictions here works because in renormalizable theories you can redefine some of your basic parameters (mass, charge...
Helicity is not a good quantum number for a massive particle (like a neutrino). Since it is roughly speaking defined as a projection of a particle's spin onto its momentum, one can always switch to a reference frame that is moving faster then the particle. In this frame you'll observe opposite...
Photons do not annihilate because they do not interact directly -- there is no such term in the QED lagrangian.
On the other hand, total aanihillation of neutron and anti-neutron is as likely as the annihilation of proton and anti-proton -- you have to arrange for interaction of three...
To answer the original question, nuclear force has a property of "saturation" related to the short-range nature of it mentioned earlier (classical analogy: if you have many marbles in a sack and ask a question how many marbles will any given marble touch at one time, the answer will always be...
No, what I'm saying is that if 4th gen exists these couplings should be very small (such that V_t'b Vt'd m_t'^2 times usual hadronic stuff for t' contribution to B-Bbar mixing parameter \Delta m_B is smaller then current theoretical and experimental errors), not necessarily zero. So it would...
4th generation quarks are searched for by studying the processes like B-Bbar (D-Dbar, K-Kbar) mixing and flavor-changing neutral current transitions, where 4th generation affects the mixing/decay parameters via loop diagrams. So far, everything is fine without the 4th generation (agrees with...