All Questions
229,900
questions
4
votes
1
answer
89
views
Introduce Ghost Field to eliminate unphysical degrees of freedom in case of Photon Field
In wikipedia's article about ghost fields is mentioned that
An example of the need of ghost fields is the photon, which is usually described by a four component vector potential $A_{\mu}$, even if ...
- 1,323
1
vote
1
answer
44
views
For a classical scalar field, how can a mode have different energies if the energy is the mode's frequency of oscillation in time?
For a classical real scalar field $\phi(\vec{x},t)$ of the type:
$$\frac{\partial^2\phi}{\partial t^2}-\nabla^2\phi+m^2\phi=0$$
The modes $\phi(\vec{p},t)$ can be obtained by:
$$\phi(\vec{x},t)=\int \...
- 536
0
votes
0
answers
64
views
Experiment about a sphere in a tube in presence of viscous resistance
Recently, I carried out an experiment at home with little equipment, but I can't get to the bottom of it. Consider a fluid-dynamic resistance force of intensity $F_L$ ($\vec F_L = - \alpha \vec V$) ...
- 371
-2
votes
0
answers
14
views
Neutrino Free streaming
I want to get to the relation which is the neutrino free streaming scale $K_{fs}$, at $\frac {T_{\nu,0}}{a^2}= \frac{1.946}{a^2}$
which is:
$K_{fs}=\frac{1}{X_{fs}}$
Finally what I want is
$K_{fs}=3.2 ...
- 27
0
votes
0
answers
22
views
What's the difference in chemical potentials between nearly free electron model and tight-binding model?
In nearly free electron model, we know that when temperature is zero, the chemical potential $\mu$ is same as the Fermi energy $E_F$, $\mu=E_F$. For a good metal, $E_F$ is roughly $10\mathrm{eV}$, so ...
-1
votes
0
answers
42
views
How can i find the electric field? [closed]
A square area of edge length L is located in the XY-plane and centered at the origin. This area is filled with
a uniform surface charge of 10-4 C/m2.
• Find the electric field (magnitude and direction)...
0
votes
0
answers
12
views
Understanding Wyckoff Position of Apatite group
I was learning about Wyckoff position, and one of the simplest example was of $ZrO_{2}$. For Zr and O, the Wyckoff positions are 4a and 8c and belongs to space group Fm-3m. Now from the Wyckoff ...
7
votes
2
answers
453
views
Can spinors be explained or understood without representation theory?
Vectors, either as abstract mathematical elements of a vector space (in this case the definition of the vector is divorced from any notion of transformation), or as elements of tangent spaces on ...
- 12.9k
0
votes
0
answers
35
views
Solving the flatness problem without inflationary-model dependance
I am working through some Cosmology questions and I want to find a minimum number of e-folds to obtain a certain value of the density parameter $\Omega_T$ at the time of BBN that would explain the ...
-1
votes
0
answers
28
views
Tangential Velocity of a Wheel Connected to a Rigid Link While Passing the Ramp [closed]
As seen in the figure, the rigid link moves at constant velocity (V) on the x-axis. This rigid link is connected to the tractor on the x-axis from one end and to the wheel from the other end with ...
- 1
2
votes
1
answer
200
views
Chemical potential of an ideal quantum gas
As far as I understand from textbooks, absolute values of the chemical potential are meaningless, only changes have physical meaning. That would mean that, from statistical mechanics, one should only ...
- 974
-1
votes
1
answer
28
views
Objective dimensional manipulation [closed]
Question,
If you exerted enough heat energy into a place in the cold boundless vacuum of space could you transfer that work into acceleration of the expansion of the universe in that locale? Are there ...
-1
votes
0
answers
24
views
I want to know if self-inductance will play a role in the emf [closed]
In figure the mutual inductance oof a coil and a very long staright is M the coil has resistance $R$ and self-inductance $L$ the current is the wire increases at a rate of $b$ where b is a constant ...
- 1
3
votes
0
answers
75
views
Resources for Noether's Theorem (First and Second) including in a General Relativistic Context
I'm after any in-depth expositions on Noether's Theorems, especially graduate-level textbooks, which include application/discussion in a general relativistic context. Strangely enough I don't see it ...
1
vote
0
answers
30
views
Quantum corrections in Holography
AdS/CFT stablish that there is some kind of correspondence between the ${\cal N}=4$ SYM theory and strings in $AdS_5\times S^5$ space-time. I know, for instance that 1/2 BPS operators like Tr$(\phi_1^...
- 331
-2
votes
0
answers
25
views
Centre of mass (two mass block and spring problem) [closed]
Consider the situation of the previous problem. Suppose the block of mass m1 pulled by a constant force f1 and the other block is pulled by a constant force F2. Find the maximum elongation that the ...
- 1
0
votes
0
answers
34
views
Expected number of particles [closed]
My question is about probability in quantum mechanics.
A wave function in quantum mechanics is understood in terms of probability and trials. Let's consider a wave function over a region of space ...
0
votes
0
answers
11
views
Coupling three Ising chains via an energy-energy-energy interaction
I want to note that this question is related to another one I asked involving just two chains coupled by an energy-energy interaction. I'm choosing to ask them separately because I suspect they may ...
- 1,624
-1
votes
0
answers
18
views
Vector Potential for Infinite Slab with Non-Uniform Current Density [closed]
How would I go about finding the vector potential for the inside and outside of an slab that's infinite in the x and y plane (finite in the z plane), with a non-uniform current density along the x ...
- 1
0
votes
0
answers
13
views
Isotropic classical model with a different phase transition than its anisotropic quantum limit
I have often heard that the isotropic ferromagnetically-coupled 2d classical Ising model and the quantum 1d transverse field Ising model have similar phases and the same universality class of their ...
- 1,624
0
votes
0
answers
15
views
Does anyone know the correct way to verify the color temperature of a given light source in a color booth and the equipment needed?
ie. spectroradiometer on the floor (constant distance) of the booth directly measuring the "observed" color temp emitted directly from the light source? is it more acurate to measure the ...
- 1
0
votes
0
answers
35
views
feynman scalar integral with on-shell condition
There are many integration written down in the standard QFT textbooks for scalar integrals in the computation of matrix elements. For example, in Peskin and Schroeder, we see
$$\int \frac{d^d \ell_E}{(...
- 975
1
vote
0
answers
24
views
Landau Ginzburg path integral (PI) for the Ising model at gaussian order
I am stick with a problem in computing explicitely the gaussian PI in the Landau-Ginzburg theory for the Ising model.
If we do a procedure of coarse graining, we can define $m(x)$ as a continuous ...
2
votes
0
answers
95
views
Mathematical objects on crystal meltings and their relation to particle physics
I am a mathematician interested in analytic number theory, and I found the paper Dimers and Amoebae
, which shows how many mathematical objects like the Mahler measure, the Ronkin function and the ...
- 145
3
votes
1
answer
331
views
Wave amplitude as a complex number?
In section 1-3 An experiment with waves of The Feynman Lectures on Physics (https://www.feynmanlectures.caltech.edu/III_01.html) it says:
"The instantaneous height of the water wave at the ...
- 157
0
votes
1
answer
44
views
Why is the $ΔT$ for the heat transfer of the copper segment, like in the picture, $(100 - T)$ instead of $(T - 100)$? [closed]
Image taken from the linked video
So, I was trying to figure out the answer for a problem very similar to the one in this video, where I have to find the temperature T at the middle of the ...
0
votes
0
answers
43
views
Trajectory Equation for Pitched Baseball [closed]
I am working with a [NASA Curveball simulator] (https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/ballkiosk/) and am trying to come up with equations to match its results. Unfortunately, [NASAs ...
1
vote
0
answers
33
views
Coupling two Ising chains via an energy-energy interaction
Consider the transverse-field Ising model on a chain with periodic boundary conditions:
$$ H = -\sum_{i=1}^{L} \sigma_{i}^z \sigma_{i+1}^z + h \sigma_{i}^x$$
There's a phase transition at $h=1$, which ...
- 1,624
0
votes
0
answers
65
views
Doesn't matter collapsing inside a black hole spin at the speed of light?
Once an event horizon is formed in the process of the gravitational collapse of a star, the original star collapses inside the event horizon. As far as we know, stars and in particular neutron stars, ...
- 378
0
votes
1
answer
56
views
Are creation and annihilation operators functions of momentum?
In QFT, we usually write creation and annihilation operators in the following way: ${a^s_{\textbf{p}}}^\dagger$, $a^r_{\textbf{q}}$, where $r,s$ denote the spins and $p,q$ the three-momenta of ...
- 258
0
votes
0
answers
14
views
Change of scaling due to a perturbation
I am looking for known examples of models where the introduction of a perturbation changes the scaling law of one or more observables.
I would appreciate suggestions relevant to any branch of Physics, ...
- 1,180
0
votes
0
answers
22
views
Is the normal to an embedded surface generally undefined up to a connection?
Let there be an embedding $\phi:S\rightarrow M$ where $M$ is a d-dimensional manifold and $S$ is a codimension-k submanifold. the space of all tangent vectors to the embedded surface $\phi(S)$ is ...
- 4,473
0
votes
1
answer
60
views
How to find the optical path difference between two non-parallel light rays?
Consider this Thin Film Interference diagram here.
The Optical Path Difference (${OPD}$) between the reflected light rays from ${C}$ and ${A}$ is
$$OPD = n_{2}({AB} + {BC}) - n_{1}{AD}.$$
I can ...
- 101
-4
votes
0
answers
31
views
AC Node analysis [closed]
i want to ask about the concept of ac anlysis
in the following question,i want to find the value of Vc
here is the soluion
Here is the equation to find out the value of Vc
I know i1+i2+i3=0
in the ...
- 1
2
votes
1
answer
51
views
What causes this fluorescence-like effect?
I have a New Year's garland that emits blue light:
When I turn it on and turn off all other lights in the room, almost all objects in the room would be colored in different shades of blue - as I ...
0
votes
1
answer
31
views
Light doppler effect to low velocity [closed]
Show that for low speeds the Doppler effect of light can be written in the following approximate form: $$\frac{\Delta \lambda}{\lambda} = \frac{v}{c}.$$
I don't have many ideas. Can anyone help me?
- 1
0
votes
0
answers
29
views
Frequency Dependent Absorption According to Wu
I was reading the paper "Theory of strong-field attosecond transient absorption" by Wu, and he says that the difference in energy of a material interacting with an electromagnetic field (...
0
votes
0
answers
16
views
What is the point of the booster/sonotrode combo in an ultrasonic cutter? Can it be replaced with a single flat sheet of metal? [closed]
I want to make an ultrasonic cutter for home use projects, something like this or there are many online videos of industrial ultrasonic cutters in e.g. the food industry. A typical design of an ...
- 169
0
votes
1
answer
22
views
How does photoelectron yield quantum efficiency change for metals in presence of electric field?
Figure 1 of this paper gives quantum efficiency for stainless steel. https://arxiv.org/pdf/1503.08074.pdf
However, I am interested in photoelectron yield quantum efficiency for stainless steel at 4kV/...
-2
votes
1
answer
30
views
Difference between friction force and force because of friction?
I'm doing some physics studying right now and the wording of an example question really confused me so I was hoping to get help in figuring it out. It says that " The coefficient of friction ...
0
votes
0
answers
54
views
Explicit Form of Feynman Propagator for a Scalar Field in Position-space: Derivation Details
This is Problem (6.1) from Schwartz's QFT and the Standard Model. I am trying to directly calculate, by performing the integral over momenta, the explicit position-space expression of the Feynman ...
- 19
-2
votes
1
answer
61
views
About Second-Order Poles of Matsubara Sum
I would like to ask about the calculation regarding Matsubara sum of the form
\begin{equation}
\frac{1}{\beta}\sum_{i\omega_n} \frac{1}{(i\omega_n-\xi)^2}
\end{equation}
which is a second order pole ...
- 1
2
votes
2
answers
100
views
Book on numerical solution of PDEs
I would like to learn how to solve partial differential equations (first and second order, e.g. Poisson, etc...) numerically with finite differences. Which book can be recommended if one want it to ...
0
votes
0
answers
18
views
What happens to the material within a pin when it is sheared? [closed]
how do I explain what is going on within a cylindrical pin when it fails due to shear stress?
specifically what happens within the material to produce the grooves and the messed up area shown in the ...
-1
votes
0
answers
33
views
Capillary Rise and Orientation of the beaker
When a capillary is dipped vertically inside a liquid, the liquid rises upto a height $h$. In the same capillary, the same liquid is filled in horizontal position, then it is kept in a vertical ...
2
votes
1
answer
56
views
Post-Newtonian Stress-Energy tensor
I am currently studying Michele Maggiore's book - 'Gravitational Waves: Volume 1: Theory and Experiments'. On pages 245 and 246, each order --- until the second order --- of the stress-energy tensor. ...
- 1,151
2
votes
0
answers
44
views
Unable to re-derive Inverse Transfer Matrix
I don't get the same result as the book when computing the inverse of this matrix.
For context, I'm rederiving some equations from a book on acoustic waves in periodic structures, specifically a ...
- 21
0
votes
2
answers
46
views
Confusion in calculation of power [duplicate]
Question-
Sand is being dropped from a stationary dropper at a rate of 0.5 kg s$^{-1}$ on a conveyor belt moving with a velocity of 5 ms¹. The power needed to keep belt moving with the same velocity ...
- 202
2
votes
0
answers
57
views
Newtonian 2-Body problem
The Newtonian equations of motion for two-point masses $m$ and $m^{\prime}$ are derived from the following Lagrangian:
$$L = \frac{1}{2}m\mathbf{v}^{2} + \frac{1}{2}m^{\prime}\mathbf{v}^{\prime \, 2} +...
- 1,114
0
votes
0
answers
21
views
de Sitter spacetime, spacetime without boundaries and holographic principle
One of the most intriguing aspects of black hole thermodynamics is that of holography or the holographic principle, namely, that the degrees of freedom of a putative theory of quantum gravity is ...
- 6,379