What is the acceleration rate of a neutrino? I understand that photons do not have acceleration because they are massless. But what about neutrinos, which have been proven to have mass due to oscillation? Let's assume a typical Solar neutrino with an energy of 1 MeV.
Related question: what is the acceleration rate of the Oh-My-God particle?
 A: A neutrino is a little like a bullet. It is launched at high speed, and not much happens after that.
A neutrino is only affected by gravity and the weak force. It is not affected by electromagnetism or the strong force.
All the everyday forces we experience are gravity and electromagnetism. These forces are long range forces.
$$F_{gravity} = G \frac{m_1m_2}{r^2}$$
$$F_{electrostatic} = 4\pi \epsilon_0 \frac{q_1q_2}{r^2}$$
where $r$ can be as big as you like.
By contrast, the strong and weak forces are short range. They are a little like Velcro. The force is present when things are very close together, but gone when separated even a little. Their range is far smaller than the diameter of an atom. Typically, they act within the nucleus of an atom.
Gravity will slow a neutrino as it escapes from the Sun. But a relativistic particle is going so fast that this is not a significant effect.
Neutrinos very seldom interact with matter. The odds are overwhelming that for any Solar neutrino detected on Earth the detection is the first interaction since leaving the Sun.
So the neutrino arrives with just about the same speed it had when it was created by a nuclear reaction in the core of the Sun.
When dealing with such short distances and small particles, everyday Newtonian mechanics does not describe it well. So it isn't right to say that the neutrino accelerated from a speed of $0$ over a distance no more than the diameter of a proton or so. It is better to say that creating the neutrino left it in a state where it had that energy. From the mass of the neutrino (which we don't know very well) you could figure out a speed. Given that the mass is very small, the speed is very close to c.
