15 questions linked to/from Why can't gauge bosons have mass?
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### Why do we believe local gauge invariance (that tells us photons are exactly massless)? [duplicate]

There are experimental upper limits on the photon's mass, but they are finite. I heard that the reason we know that photons have exactly zero rest mass (and thus travel exactly at the universal ...
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### Can you give a photon mass? [duplicate]

I know this may sound weird. But could a photon be given mass? And if so what would the effects be?
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### Why can't photons have a mass?

Why can't photons have a mass? Could you explain this to me in a short and mathematical way?
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### Why does transition from one electron shell to another shell always produce massless photon?

When electrons transition from a higher energy state to a lower energy state (energy difference $E$), they produce massless photon with frequency $\nu$ where $\Delta E= h \nu$ (h is Planck ...
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### What will happen if the photon has non-zero mass?

I want to know the theoretical implication if photons have a non-zero mass. What happens to the Maxwell equations? What happens to QFT? If the photon have mass it can decade?
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### What prevents photons from getting mass from higher order Feynman diagrams

The Higgs boson and gluons have no electric charge and photons couple to charge, so there is no tree level interaction between them and photons. But what prevents higher order diagrams from ...
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### Problems with putting mass on Yang-Mills theory by hand

When Yang-Mills field theory was introduced, a problem is that the gauge invariance can not allow mass for the gauge field. Later people invented spontaneous symmetry breaking and Higgs mechanism to ...
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### What evidence is there for the electroweak higgs mechanism?

The wikipedia article on the Higgs mechanism states that there is overwhelming evidence for the electroweak higgs mechanism, but doesn't then back this up. What evidence is there?
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### How does gauge invariance prevent the photon from acquiring a mass?

I have read that the photon is protected from acquiring a mass due to gauge invariance. However, I was under the impression that gauge invariance is not a true physical symmetry, but rather a ...
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### $U(1)$ local gauge invariance in QED [duplicate]

While constructing Lagrangian of QED, we don't add the mass term for photon $\dfrac{1}{2} m^{2}A_{\mu}A^{\mu}$ because gauge invariance does not allow. I want to ask, whether "$\bf{Theoretically}$", ...
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### What is the problem with a Lagrangian that isn't gauge invariant?

In every textbook I've read the only argument why gauge bosons can't have mass is "because a mass term would break gauge invariance". Even fermions can't have mass because it would break the $SU(2)_L$ ...
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### Masslessness of the electromagnetic field

Why is the electromagnetic field massless? I presume the mass term in the Lagrangian, $$\dfrac{1}{2}M^2 A_{\mu}A^{\mu},$$ would "violate" gauge redundancy. But this is what its name indicates: ...
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### Why can't we give photon mass in vacuum? [duplicate]

Would it violate any special laws, if someone were to change the axiom of SR that "Speed of light in vacuum is the same with respect to all reference frames" To "Speed of light in vacuum is ...