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  1. K

    I Direction of an ionized electron's travel

    Hello! If I have an atom traveling with a given velocity and I ionize it in flight, will the electron remain at the place of ionization, or it will travel at the same speed along with the resulted ion? Thank you!
  2. K

    I Spontaneous symmetry breaking from a QM perspective

    Hello! This questions might not make sense and I am sorry if that is the case (I am asking from a QM class perspective). I am a bit confused about the idea of spontaneously symmetry breaking (SSB), from the point of view of QM. I am talking here about the energy plot looking like a mexican hat...
  3. K

    PRL impact factor

    Why does PRL have such a small impact factor? There are so many great papers published there (if I am not wrong the Higgs discovery, too?), how do they define the impact factor of a journal?
  4. K

    Physics Do you need a Master's degree to teach physics at an American university?

    Hello! Do you need to have a master on top of a PhD to teach at an American university? I see that most programs for PhD start right after undergrad and they are about 5-6 years and they give your a doctorate degree. Do you also get a master degree on top, or is that something separate you need...
  5. K

    I Nuclear charge radius formula

    Hello! Can someone point me towards some papers/readings providing formulas (derived theoretically or based on experimental data) for the nuclear charge radius? Almost all the papers where I found a formula for that are of the form ##aA^b+c##, where a, b and c are constants and A is the mass...
  6. K

    I Using AI for gravitational waveform generation

    Hello! Can someone point me towards some papers that use AI for gravitational wave generation? I found many papers using AI to analyze data, but not really something where AI is used to actually generate waveforms. For example this was done for particle physics simulations to increase the speed...
  7. K

    I Subtracting background from data

    Hello! I have some counts measured at fixed points, both for background only and signal+background. Say that for a given x I have 16 counts with background only and 100 for background+signal. So the background is ##16\pm 4## and for the signal+background ##100\pm 10## (assuming poisson...
  8. K

    I Born-Oppenheimer approximations in molecules

    Hello! I am a bit confused about Born-Oppenheimer approximations in molecules (mainly diatomic ones). It seems that all the books where I read about it, it is presented as a major breakthrough (at least in the context of molecular physics), but when I look into it in more details, it seems to...
  9. K

    I CM frame kinetic energy for a molecule

    Hello! When the kinetic energy of a molecule is written in its CM frame we get the formula attached. The first term is the kinetic energy of the CM frame with respect to the lab frame, the second term is the kinetic energy associated with the distance between the nuclei and the last term is the...
  10. K

    I Linear fit on the difference of data points

    Hello! I have some data points obtained from a measurement and one of them is defined as the reference point. I need to compute the difference between that reference point and all the others (including itself) and plot the difference as a function of another variable (which doesn't have an error...
  11. K

    I Vibrational energy in molecules

    Hello! I am not sure how to visualize (ideally in a simple, classical way) the vibrational energy levels of a molecule. For the electronic levels (similar to atoms), I usually think of it as the atom having multiple energy levels (fixed in space, in a probability distribution sense), and when...
  12. K

    I Classical rotation

    Hello! I am a bit confused by the reference frames used in derivations for rotational motion in classical mechanics (assume that there is no translation and the body rotates around a fixed point). As far as I understand there are two main frames used in the analysis: a lab frame, which is fixed...
  13. K

    I Rotation in molecules

    Hello! I am a bit confused about the rotational motion in molecules. Assuming the bond length is constant, the motion can be described as a rigid rotor. In the center of mass frame the energies are given by ##BJ(J+1)## and the wavefunctions are spherical harmonics. However when we measure the...
  14. K

    I Nuclear rotation wavefunction

    Hello! I am a bit confused by the quantum numbers used to describe the rotation of a nucleus. In Wong's book these are J, M and K, which represent the rotational quantum number, its projection along the lab z-axis and its projection along the body intrinsic symmetry axis, respectively. However...
  15. K

    I Quadrupole deformation in nuclei

    Hello! I am confused about the definition of the quadrupole moment in nuclei. One definition I found, in Wong, says that the quadrupole moment of a nucleus is given (ignoring some numerical constant) by: $$<J,M=J|r^2Y_{20}|J,M=J>$$ so the expectation value of a second order spherical harmonic...
  16. K

    I Static and dynamic excited states

    Hello! I am reading about excited levels in nuclei (I am mainly following Wong's nuclear physics book) and I am a bit confused about the nature of the excited states. In the one particle picture (mainly shell model) the excitation appears as static i.e. one nucleon moves from a certain orbital...
  17. K

    I Simple explanation for cross section ratio

    Hello! Is there any simple (i.e. using some physics arguments, without actually doing the math) explanation for why $$\sigma(pp \to \pi^+d)/\sigma(np\to\pi^0d)=2$$ where d is the deuteron? Thank you!
  18. K

    I Isotope shift in molecules

    Hello! Is the isotope shift between 2 (low lying) vibrational levels of the lowest 2 electronic levels (of a diatomic molecule) the same, no matter what the 2 levels are? For example, is the isotope shift associated to the ##0 \to 0## vibrational transition of 2 molecular isotopes (here I mean...
  19. K

    I Errors on linear fit

    Hello! I made a linear fit, ##y=ax+b##, to some data points and I get the best parameters with their (1 sigma) errors: ##a\pm\delta a## and ##b\pm\delta b##. I want to plot this fit on top of my data points in such a way as to reflect the error on the parameters. The "main" fit is simply...
  20. K

    I Scalar Hamiltonian and electromagnetic transitions

    Hello! This is probably a silly question (I am sure I am missing something basic), but I am not sure I understand how a Hamiltonian can be a scalar and allow transitions between states with different angular momentum at the same time. Electromagnetic induced transitions are usually represented...
  21. K

    I Low-lying excited states in nuclei

    Hello! How are the parity and spin of excited states of nuclei measured experimentally. I imagine that the energy can be easily measured by exciting the nucleus (by colliding it with a nucleon or electron for example) and then measuring the emitted photons. But how can one infer the spin and...
  22. K

    I Nuclear force behavior

    Hello! I am confused about when the nuclear force is attractive and when not. Based on deuteron (the book I am following is Wong), we see that we can't have bound state with isospin T=1 (otherwise we would see, for example, a stable double neutron and no proton nucleus). Also, in the book I see...
  23. K

    I EDM and time reversal

    Why for some systems (such as the electron or neutron) the presence of an electric dipole moment (EDM) implies time reversal violation, while for others, such as water molecule, this is not the case? Thank you!
  24. K

    I Decoupling of angular momentum

    Hello! I am reading some papers and I often noticed that it is mentioned that a strong magnetic field is able to decouple certain angular momenta from each other. For example in this paper: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.100.023003 they present a Hamiltonian (second column...
  25. K

    I Input/output coupling of a cavity

    Hello! I am reading some stuff about building optical cavities, mainly a bow-tie cavity. Is there anything special about the input/output coupling in terms of design? I understand that these are the mirrors used to send the light inside the cavity and read some signal out of the cavity, but are...
  26. K

    I Vector addition in spin orbit coupling

    Hello! I am reading about spin-orbit coupling in Griffiths book, and at a point he shows an image (section 6.4.1) of the vectors L and S coupled together to give J (figure 6.10) and he says that L and S precess rapidly around J. I am not totally sure I understand this. I know that in the...
  27. K

    I Transitions in diatomic molecules

    Hello! I started reading some stuff about molecular spectroscopy and I see that the changes in the total angular momentum, J, can be -1, 0 or +1 (corresponding to the P, Q and R branches). Is this because the photon carries a spin of 1? Also is this the most general case (assuming only EM...
  28. K

    I Ligo heat dissipation

    Hello! I am not sure I understand how the heat from the lasers get dissipated in LIGO, at the mirrors. Given the high power of the lasers, the mirrors heat up, but the setup is in vacuum, so it is difficult to get rid of that heat. How do they make sure that the mirrors don't get too much damage...
  29. K

    I Nuclear force potential

    Hello! In Nuclear Physics, Second Edition, by Samuel Wong he shows a plot of the nuclear potential (see attached) but he also gives a formula (also attached) for the most general way of writing the nuclear potential. In that formula, we have the coefficients depending on r only, but the overall...
  30. K

    I Coherent neutron scattering

    Hello! I am not sure I understand how neutron coherent scattering takes place. The case I am particularly talking about is neutron scattering off a hydrogen molecule. When thinking of Coulomb interaction, I would imagine this as if the incident particle (not a neutron, as the neutron doesn't...
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