# Tag Info

88

Things are not empty space. Our classical intuition fails at the quantum level. Matter does not pass through other matter mainly due to the Pauli exclusion principle and due to the electromagnetic repulsion of the electrons. The closer you bring two atoms, i.e. the more the areas of non-zero expectation for their electrons overlap, the stronger will the ...

16

With a sufficient "tolerance", one may of course envision forces that are weaker or much weaker than gravity. Experimentally, one may only improve upper bounds on the strength of the new forces. On the other hand, there exist rather strong theoretical arguments that gravity actually has to be the weakest long-range (power-law) force for the consistency of ...

9

For forces that can be expressed in terms of a quantum field theory, you can compare the size of the coupling constants (which are dimensionless). In short this means that perturbative expansions of weaker forces are well represented by a small number of leading terms because the series converges quickly, while those of stronger forces require more terms (or ...

8

The neutrino and the anti-neutrino can annihilate to create a $Z$ boson. But the mass of the $Z$ boson is around $90$ GeV, so in order to create such a boson, the neutrinos need to be high energetic. Theoretically, a Higgs boson could be created as well, but for that an even larger amount of energy is needed, since the Higgs boson is heavier than the $Z$ ...

8

Does a particle enter/interact with the Higgs Field when created, or at some other time? After reading your question a couple of times as well as your comments, it occurs to me that you're picturing something like this: a massless particle is created, interacts once with the Higgs field to acquire a permanent classical like mass which it then ...

7

I don't think you understand QFT. To be fair, I'm no expert myself, but I can certainly point out where you're going wrong here. A particle does not enter the Higgs field. However, the particle field that gets mass from the Higgs field does interact with the Higgs field. What this means is that in the Lagrangian of your model, there exists a term that will ...

7

If it were possible for one object to pass through another object, then it would be possible for one part of an object to pass through a different part of the same object. Therefore the question asked here is equivalent to the question of why matter is stable. See this question on mathoverflow. That question was more about the stability of individual atoms, ...

6

When supernovae go bang they emit light (obviously) but they also emit neutrinos. Since neutrinos are massive (well, at least two out of the three types of neutrinos) we would expect them to travel slower than light, so at a first glance you might expect the light from the supernova to arrive before the neutrinos. However the neutrinos from 1987a were ...

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 ...

6

Anomalies (not anamolies) are a whole subject whose basics are covered by one or several chapters of almost any good enough quantum field theory textbook so it's counterproductive to retype this whole chapter here. But generally, in quantum field theory, anomalies are quantum mechanical effects breaking symmetries that exist in the classical theory – ...

6

Gluons are bosons, they have spin one and are mediators of the strong force. They have mass 0 and there is no weak interaction vertex with a gluon. The extract is talking of the Higgs field, not the Higgs boson. A field in physics is A field is a physical quantity that has a value for each point in space and time at that point. The Higgs field ...

6

Don't think about annihilation as something exceptional. Annihilation is just a type of interaction and there are many other possible interactions. Now I don't use the word "interaction" in the sense of "4 fundamental interactions", but in the sense of possible process in the quantum world where particles are destroyed and created. So the question should ...

5

At first, consider two particles decay: $A\rightarrow B + e^-$ Where A is initially rest. So $\vec{p_B}+\vec{p_{e^-}}=0$ now \begin{align} \frac{p_B^2}{2m_B}+\sqrt{p_{e^-}^2+m_{e^-}^2}&=E_{released} \\ \frac{p_{e^-}^2}{2m_B}+\sqrt{p_{e^-}^2+m_{e^-}^2}&=E_{released} \tag{1} \end{align} see here you have uncoupled equation (equ.1) for $p_{e^-}$ ...

5

Yet there are all kinds of reactions that cause light, seemingly without providing the infinite amount of energy needed to accelerate particles to light speed. If you're imagining that there are photons at rest within the flashlight when it's off and the flashlight accelerates photons to light speed when it's turned on, then I can see why you're ...

5

[...] $\Delta^+ \rightarrow p + \pi^0$, [...] $\Delta^+ \rightarrow n + \pi^+$, which process is favored: the proton and neutral pion or neutron and charged pion [?] Since the kinematics (and corresponding "phase space" factors) for the two final states are presumably as good as equal, the evaluation of the branching ratio $$\text{BR} := ... 4 From an experimentalist's point of view in order to measure something or set a limit, a specific theoretical framework has to exist. Take as an example the limits measured for the electric dipole moment of the electron. The experiment is specifically designed on the supposition that the signal will come from a T asymmetric theory proposed. As you can see ... 4 There can certainly be extra forces. For example the Higgs particle can be regarded as the carrier of a fifth force, though as you'll see from the answers to that question whether or not this is really a fundamental force is debatable. More generally there have been discussions of possible extra forces for decades, for example Brans-Dicke theory postulates a ... 4 Yes, the Z boson can decay into a neutrino and anti-neutrino, and the process you describe is just the time reverse of this. 4 First, note that we are quite sure what the overall nuclear spin is; we are not sure how to obtain it mathematically from available models. Due to the phenomenon of color confinement, there are no gluons at low energies in QCD (the theory underlying nuclear physics). Importantly, you can't say there are this or that many gluons in any proton or neutron. ... 4 The history of high energy physics is in the words "high energy" . There are two ways to get it, building higher and higher energy accelerators or studying cosmic rays, which last has answers in another question. Accelerators are of two types, those creating beams of particles that fall on fixed targets, and colliders, having two beams collide. All ... 4 It takes an infinite amount of energy to accelerate a particle with mass to the speed of light. A photon does not have mass, thus can move at the speed of light. Note that a photon does not accelerate; the moment it is created it moves at the speed of light. 3 First, the electron isn't actually spinning. Physical objects made up of collections of electrons and protons (and neutrons) can have angular momentum because they rotate; the electron does not get its angular momentum for the same reason. Second, the magnetic moment of an object with angular momentum L is proportional to$$ \mu \propto \frac{qL}{M}  ...

3

The Higgs field is not giving mass to all other particles. There are particles that acquire mass differently - for example neutrinos. Or the yet undiscovered particles of dark matter probably don't get mass from the Higgs field. Also please notice the difference between the Higgs field and the Higgs boson. The Higgs field is giving mass to some particles, ...

2

There is some debate about whether it exists or not, but there has been some research into what is called a quark star. This article (should be a free link, but here is the arXiv version in case) suggests that A recent calculation for cold and dense QCD strange quark matter including corrections to order $O\left(\alpha_s^2\right)$ indicates that ...

2

A good place to look to get an idea of the experimental bounds is at Eötvös experiments, which attempt to measure deviations in the inertial mass from the gravitational mass. Another way to think about this, is if there was a force we can not yet model, it would show up as an effective change in the inertial mass in these experiments. So far, these ...

2

No, only some baryons form a decuplet under SU(3) flavor symmetry, specifically those 10 spin 3/2 baryons formed from up, down,and strange quarks,depicted in the following diagram (figure credit Wikipedia baryon article , figure listed as public domain): On the diagram $Q$ is electric charge, $I_3$ is isospin, and $S$ is the strangeness quantum number. ...

2

The electron and the photon are elementary particles, quantum mechanical entities, which given the boundary conditions of the setup will sometimes display characteristics of particles, i.e. trajectories and impact points, and sometimes display characteristics of probability waves, as in the two slit experiment. In impact situations where only the momentum ...

2

As pfnuessel said in his comment: The first thing to look at was the Higgs - there were hints from LEP and Tevatron, but no evidence, so the LHC was designed that the (SM-)Higgs has to be seen, if it exists. And for everything beyond the Higgs - we don't know! There are various theories, e.g. the different flavors of super-symmetry and others, but they all ...

2

A group $G$ by itself is not a group of linear transformations, it is an abstract algebraic object. Only its representations map its elements (injectively if the representation is faithful) to elements $\mathrm{Aut}(V)$ of some vector space $V$. Now, physics seems to have no need of such abstract language at first. Our "vector space" is pretty much our ...

2

At the end of the day, the diagram shows the distribution in angular differences between pairs of charged particles produced in the collisions. $\Delta \phi = \phi_1-\phi_2$ is the difference in azimuthal angles $\phi$ of those pairs. $\Delta \eta = \eta_1 - \eta_2$ is the difference in pseudorapidities $\eta$ of those pairs. The $\phi$ and $\eta$ ...

Only top voted, non community-wiki answers of a minimum length are eligible