# Tag Info

## New answers tagged quarks

1

A (on-shell) quark has fixed mass. It's energy depens on the frame of reference you use for asking the question. Mass is a Lorentz scalar (i.e. is invariant). Energy is one component of the energy-momentum four-vector and is not invariant.

2

The upper mass limit for a quark star depends on your assumptions and ranges between 1 and 2 solar masses (cf. this paper (arXiv link) from 2001). It seems to me that the reason for the similarity to neutron stars' mass range is that it both compact objects satisfy the TOV equation, $$\frac{dp}{dr}=-\frac{G}{r^2}\left[\rho+\frac{p}{c^2}\right]\left[M+4\pi ... 1 About the supposed paradox: u and \bar d have the same isospin quantum numbers, but not all the other properties. If you restrict your problem to only study the isospin space, you will not see that they have different charge and other different quantum numbers. About the charge: I don't know where your equation comes from, but it seems close to the ... 1 Almost nothing. Hawking was probably just building up to the fact that quarks are "colored" under the strong interaction force (a whimsical name, nothing more), but not actually colored in terms of visible electromagnetic radiation. Collections of atoms/molecules that really are about the same size as visible light wavelengths tend to scatter all frequencies ... 6 It doesn't matter whether the b-quark is highly energetic, it can never decay to a top quark and a W-boson if it is on mass shell, by which I mean, p^2=E^2 - \vec p^2 =m_b^2. To see this, consider energy-momentum conservation,$$ b^\mu = W^\mu + t^\mu \Rightarrow m_b^2 = M_W^2 + m_t^2 + 2W\cdot t = M_W^2 + m_t^2 + 2 E_t M_W  However, since the energy ...

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