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    I How do you get polarized charged particles?

    Hello! how does one produced big ensembles of polarized charged particles (electrons, protons, muons etc.) for certain experiments? In the case of neutral particles (for example the nucleus in an atom) this could be done using a magnetic field, but I guess this won't work that straightforward...
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    I Confused about the AC Stark effect

    Hello! Can someone explain to me in an intuitive way (or a nice mathematical demonstration) or point me towards some accessible papers about the AC Stark effect (Autler-Townes effect)? I am mainly confused by how can one start from a 2 level system (consider a 2 level system for simplicity) add...
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    I Schiff moment in classical electrostatics

    Hello! I just found out about the Schiff moment. This is the paper where I encountered it, equations 3 and 4. The paper covers other things, too, that are not related to my question. The main question I have is that, it seems like the derivation from equation 1 to 4 is purely classical (one can...
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    I T-odd vs T-violation

    Hello! I am a bit confused by the difference between T-odd and T-violation. For example, I read that the existence of a fundamental particle EDM is a violation of time symmetry. However, placing an electric dipole in an electric field, would produce a hamiltonian (non-relativistically, which is...
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    I Right way to do a linear fit

    Hello! I have some data of the form (x,y,z) which I know it is described by a function of the form: ##z=y(a+bx)##, where a and b are parameters to be fitted for. z and y have error associated to them while x doesn't (x is actually an integer going from 0 to 3 for each value of y). I tried to do...
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    I Citation for a knot theory statement

    Hello! Where can I find the source for this statement (i.e. a citation for it, ideally the original one): "any smooth k-sphere embedded in ##R^n## with 2n − 3k − 3 > 0 is unknotted". Thank you!
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    I Bad point in a linear fit

    Hello I have these points coming from different experiments: ##x = [-0.3, -0.2, -0.09, 0.01, 0.2]## ##y = [-8.15, -5.20, -3.32, 0., 5.65]## ##y_{err} = [0.1, 0.27, 0.35, 0.09, 0.44]## and I need to fit a straight line to them (based on theoretical arguments). I attached below the obtained...
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    I How to calculate the right chisquare

    Hello! I have some simulated background only data and some background plus signal simulated data. After some cuts I end up with a histogram for each of the 2 sets and I want to calculate the chisquare (and hence the p-value for a signal actually being present in the background plus signal...
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    I SXS gravitational wave data question

    Hello! I need to do some analysis for a project with the SXS gravitational wave data: but I am a bit confused about the initial conditions of their simulations. I read the paper they published about the data (it can be found at that website)...
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    I Interference intensity

    Hello! I am a bit confused by the formula for light intensity in the case of interference. In the books and online resources that I read, this is given as: $$I = I_0 \cos^2(\frac{\pi d \sin \theta}{\lambda})$$ where ##d## is the distance between the slits, ##\lambda## is the wavelength of the...
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    I Confidence intervals

    Hello! Can someone help me understand how are confidence intervals for some parameters of a fit different from the errors on the parameters obtained, for example, from the error matrix. I read Bevington and the whole book he mentions that we can use the error from the error matrix to define the...
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    I What error to use on the mean

    Hello! I have an experiment and for some reasons I was able to do only 4 measurements and they all ended up having the same value, say for the purpose of this post ##100 \pm 1## where the error of 1 is estimated based on the measuring device resolution. The mean is obviously 100. Usually the...
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    I Bin center location

    Hello! I want to plot a rate vs energy plot, but I am not sure how assign the bin center. Assume I have 2 data points in the bin (so 2 energy values), ##E_1## and ##E_2## and the first one has 100 counts measured over 10 seconds (so a rate of 10 counts/s) while the second one has 2000 counts...
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    I Neutrons inside a nucleus

    Hello! Why can't we have as many neutrons as we want inside a nucleus? I understand that for protons you have the Coulomb repulsion, but what leads to an increase of energy when adding more neutrons (which in turns lead to beta decay or fission)?
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    I How does the Pauli exclusion principle work?

    Hello! I am a bit confused about the mechanism behind the Pauli exclusion principle. From what I read, it is motivated based on QFT arguments (for example if you don't impose antisymmetry of the fermionic wavefunction you get non-locality, or infinitely negative energies etc.) so mathematically...
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    What now about Dark Matter?

    A new experiment (it's true a small scale one with the possibility of being brought to a much larger scale) has failed to find any sign of Dark Matter (DM), like all the other experiments before (at least the ground based one). AMS seems to have found some important extra anti-protons and...
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    SE tensor for scalar field

    Homework Statement Show that if the Lagrangian only depends on scalar fields ##\phi##, the energy momentum tensor is always symmetric: ##T_{\mu\nu}=T_{\nu\mu}## Homework Equations ##T_{\mu\nu}=\frac{\partial L}{\partial(\partial_\mu\phi)}\partial_\nu\phi-g_{\mu\nu}L## The Attempt at a...
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    Stress energy tensor transformation

    Homework Statement Show that if you add a total derivative to the Lagrangian density ##L \to L + \partial_\mu X^\mu##, the energy momentum tensor changes as ##T^{\mu\nu} \to T^{\mu\nu}+\partial_\alpha B^{\alpha\mu\nu}## with ##B^{\alpha\mu\nu}=-B^{\mu\alpha\nu}##. Homework Equations The...