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Gauge invariance of Hadamard point-splitting renormalization procedure

The current density of a charged complex scalar field in a background electromagnetic field $A_\mu$ is given by $$ j^\mu = ie( (D^\mu \phi)^*\phi - \phi^*D^\mu \phi)$$ with $D_\mu = \partial_\mu + ...
dolefeast's user avatar
  • 170
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1 answer
30 views

How does the induced current flow? From positive to negative or the opposite?

Let's say there's a rod and it in moving horizontally in a magnetic field (changing flux so current is induced). Using Fleming's right hand rule, we find that induced current flows from left to right. ...
android's user avatar
  • 83
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0 answers
49 views

Help in plotting the band structure of a maple leaf lattice

I was trying to plot the band structure of a maple leaf lattice. The Hamiltonian is given by: $H = t_1 \sum_{ij} (c^\dagger_i c_j + c^\dagger_j c_i e^{\phi_{ij}}) + \sum_{ij} \sum^{4}_{n=2} t_n (c^\...
Aaradhya Kulkarni's user avatar
2 votes
1 answer
86 views

Is tetrad postualte independent of gauge field?

Here is what I know, $g_{\mu \nu} = e^{a}_{\mu} e^{b}_{\nu} \eta_{ab}$ and the tetrad postulate is \begin{equation} D_{\rho} e^{a}_{\nu} = \partial_{\rho} e^{a}_{\mu} - \Gamma^{\lambda}_{\rho \nu}e^{a}...
trying's user avatar
  • 41
0 votes
1 answer
35 views

Calculating the speed of an ejected electron [closed]

I'm working on some physics exercises and came across this one. Sadly, there is no solution provided, so I was wondering if at least my line of reasoning is correct. ...
Rommelaar's user avatar
0 votes
3 answers
64 views

How is the change in internal energy zero for the following scenario:

in the problem, they are removing partitions one by one. when they remove the first partition they've mentioned in the solution that internal energy will remain constant in the process (and after ...
khan zaid's user avatar
1 vote
0 answers
45 views

DMRG for anyons

I want to do some DMRG calculations for anyons. For example, consider the golden chain model for fibonacci anyons. https://arxiv.org/pdf/cond-mat/0612341 I have two anyon types: $1, \tau$. However, ...
Souroy's user avatar
  • 163
2 votes
1 answer
83 views

As per Friedmann Equations, is big-bang singularity necessary?

The Friedmann Equations do not directly require that the scale factor $a(t)$ was zero in the beginning. Since Einstein's static universe is still a valid solution, is it possible that before the Plank ...
Nayeem1's user avatar
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0 votes
1 answer
54 views

How steep is too steep to tow a caravan up? [closed]

My family plans to buy a static caravan but we have been told it may not be possible to move it from the road onto our property. The entrance to the property is a bit steep – but is it too steep to ...
Terra's user avatar
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1 answer
96 views

Circuit quantization procedure

In circuit QED, we construct the hamiltonian of a circuit following Devoret's procedure. We start from a classical treatment, in which we impose Kirchhoff's voltage laws on fundamental loops and ...
Ric's user avatar
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Kinetic energy of a disc rotating about an inclined axis [closed]

What is the kinetic energy of a circular disc of mass M and radius R rotating with angular velocity w about an axis that is inclined to its surface by an angle of 45 degrees? (Please answer using the ...
Mansi Singh's user avatar
6 votes
0 answers
84 views

What does the word "Observable" mean in Quantum Gravity?

I have seen the statement in several places that the only "observables" in general relativity or Quantum Gravity are measured at temporal or spatial infinity. This is often used as a ...
Josh Newey's user avatar
0 votes
3 answers
39 views

Battery in non-closed circuit with charged body and Earth

Looking at the clips on how the battery works, I understand that eventually one of the ends releases the electrons which then move through the conductor to the other end, to continue the reaction. Now ...
Boris's user avatar
  • 185
0 votes
0 answers
29 views

What is the charge distribution on a parallel plate capacitor when one plate is grounded? [closed]

Let's say a large parallel plate capacitor is connected to a DC power supply. Then, the charge on the two plates will be +CV and -CV. If I ground the negative terminal (both the capacitor's and the ...
Михаил Чиланнов.'s user avatar
2 votes
0 answers
48 views

Potential of circle and $n$-gon

Consider power central fields $f \sim r^k, - \infty < k < \infty$, and unit circle, "charged" in the sense of the field. We will be interested in the potential within the circle, i.e. ...
lesobrod's user avatar
  • 163
3 votes
1 answer
170 views

Will expanding space rupture an empty box floating in outer space

Under the theory that space itself is expanding, but the space inside of atoms and molecules doesn't expand because nuclear and electromagnetic bonding forces exceed the forces that expand space, ...
mdswartz's user avatar
1 vote
2 answers
95 views

What is the correct way to think of position?

How accurate would it be to think of position (along some axis) as the component of radius vector. Example: $$ \textbf{r} = x \hat{\textbf{i}} + y \hat{\textbf{j}} $$ And if that is correct, we could ...
Alexander Djurovich's user avatar
9 votes
3 answers
1k views

Quantum: why linear combination of vectors (superposition) is described as "both at the same time"?

I want to get a better understanding of quantum phenomena and out world in general. Before long I've thought of Schrödinger cat as being both alive and dead (or spin both up and down). Now after some ...
Martian2020's user avatar
0 votes
2 answers
42 views

Could you make a fire torch with electricity? [closed]

Similar to a blowtorch, is there a way to generate a flame without using gas or liquid fuel(like butane, propane, etc)? (source) For example I'm thinking about those portable air heaters, could one ...
Gabe's user avatar
  • 193
0 votes
3 answers
65 views

Why does moment of inertia stop at 1/2 as solidness of a cylinder increases?

So I have two things about moment of inertia: The I for a hoop is $I=MR^2$ and the I for a solid disk is $I=\frac{1}{2}MR^2$ I've noticed that as "solidness" goes up from 0% (completely ...
Shelby Longbottom's user avatar
1 vote
2 answers
43 views

Viable values for the $K$ parameter in the FLRW metric

The FLWR metric is sometimes given as $$c^2 d\tau^2 = c^2 dt^2 - \frac{a(t)^2}{(1-KX^2)} dX^2. $$ I am not interested in the tangential motion so I set $d \Omega = 0$ although it is of interest in ...
KDP's user avatar
  • 5,677
-1 votes
0 answers
40 views

Frozen coffee that will not defrost at room temperature [closed]

A few weeks ago I froze some Starbucks iced mocha in an aluminum water bottle that is not insulated. Three days later the coffee which has been kept on the kitchen counter has still not defrosted in ...
Bunchy Bookles's user avatar
0 votes
0 answers
16 views

Why Does Every Member of the Ensemble Perform Work Equal to the Change in Free Energy During a Quasiequilibrium Process?

I'm studying Jarzynski's 1997 paper on the Jarzynski Equality. In the second part of the proof (from equation (9) to equation (10) in the paper), Jarzynski considers the following process: considering ...
Luessiaw's user avatar
  • 675
0 votes
0 answers
17 views

Terminal velocity of a bar magnet in a long conducting tube (quantitative)

If a bar magnet is dropped into a copper (conducting) tube, it reaches a terminal velocity. I'm trying to derive this terminal velocity. We know from Lenz's law that $e=\frac{-d\phi}{dt}$. I'm facing ...
Chirag Swarnkar's user avatar
1 vote
0 answers
26 views

What actually happens when light goes into a waveguide?

I have only dealt with a rudimentary theoretical treatment of how light propagates inside a waveguide, such as those available in Griffiths. One thing bugging me is that I still do not know how ...
hendlim's user avatar
  • 692
16 votes
5 answers
3k views

How to turn a sum into an integral?

In, An Introduction to Thermal Physics, page 235, Schroder wants to evaluate the partition function $$Z_{tot}=\sum_0^\infty (2j+1)e^{-j(j+1)\epsilon/kT}$$ in the limit that $kT\gg\epsilon$, thus he ...
GedankenExperimentalist's user avatar
3 votes
1 answer
31 views

Bloch oscillations and umklapp scattering induced by applied electric field

In Kittel's book chapter 8 there is a statement that says "The electron accelerates from k = 0 toward the zone boundary; when it reaches k = pi/a it reappears (as by an Umklapp process) at the ...
Gotaquestion's user avatar
  • 2,767
0 votes
1 answer
24 views

Flux change through a loop

I'm having difficulties understanding this thing. It would be lovable if someone could show me its derivations and prove it: In a conducting loop, there is a relationship between the total displaced ...
AhmedSahraoui's user avatar
-3 votes
0 answers
31 views

I am trying to derive an expression for the magnetic field of charged particles travelling at significant fractions of speed of light [closed]

I tried using lorentz transformation , which gives me correct answer for speed of light c but when i try to input any other values nearby c it becomes a constant B = 10-7 . q/r² ( (v - u)/ 1- uv/c²)
PhysicsEnjoyer31415's user avatar
0 votes
2 answers
146 views
+50

Do lasers with optical isolator or synchrotron radiation sources allow for Rabi cycles?

In Rabi cycle two-level system cyclically transitions between ground and excited state - bringing question where their energy difference goes during these transitions? For transition from ground to ...
Jarek Duda's user avatar
0 votes
0 answers
12 views

How do I calculate the absorption of single layers of a multilayer stack using the electric field in each layer?

I'm trying to calculate the absorbance of individual layers using the transfer matrix method but I'm stuck on how to do it. The code I am using can give the total absorbance of the system, and the ...
MOC's user avatar
  • 1
2 votes
0 answers
59 views

Under what circumstances can a 4D singularity occur in General Relativity?

I've tried to find on the literature about 4D (single point) singularities, but most of the theorems about singularities pertain to either space-like or time-like singularities, which always have some ...
UnkemptPanda's user avatar
0 votes
1 answer
23 views

Can one make a jet of air bounce without spreading?

Similar to this reaction on this image (left most) how it keeps its mass without spreading: (Video Link) Is there a way to make a jet of air bounce without spreading? (source)
Gabe's user avatar
  • 193
1 vote
2 answers
39 views

Cone vs. small circle parallel transport

I'm having trouble reconcile the following two seemingly contradicting conclusions (in 2d space): A cone is flat, because you can unfold it and it's a flat 2d surface. A cone as shown in the picture ...
Cosmo's user avatar
  • 313
1 vote
3 answers
66 views

Why do objects in circular motion move outwards instead of inwards? [duplicate]

I know that whenever an object undergoes circular motion then it has a centripetal acceleration towards the centre and a tangential acceleration. Due to these accelerations I had thought that ab ...
Madly_Maths's user avatar
2 votes
1 answer
52 views

Spinning a rope conundrum

Sometimes I will take a rope or string and spin it in the air to see what will happen. Now usually, if I am spinning it vertically, the end of the rope will extend outwards due to Newton's first law, ...
Frontiers Aerospace's user avatar
-1 votes
1 answer
69 views

What happens if we differentiate spacetime with respect to time? [closed]

Essentially, what would differentiating space-time with respect to time provide us with? What are the constraints associated with such operations? Is it possible to obtain a useful physical quantity ...
Kimaya Deshpande's user avatar
0 votes
2 answers
70 views

Regarding the absorption property of a blackbody

Consider a blackbody of surface area $S_b$ and at temperature $T_b$. It is placed inside an evacuated chamber (to neglect all the effects of convection), with walls of chamber at temperature $T_c$ and ...
CP of Physics 's user avatar
0 votes
1 answer
35 views

Is there a way to achieve a long jet of air?

As can be seen in the example image bellow from a fog/smoke generator machine, the smoke spreads as soon as it leaves the nozzle. (source) Is there a way to achieve a longer jet of air with less ...
Gabe's user avatar
  • 193
1 vote
1 answer
50 views

Permittivity real and imaginary parts with similar value possible?

Here's the context; I'm studying biological tissues that are supposed to behave like dielectrics. Using the modified cole-cole equation for theoretical predictions: $$\tilde{\varepsilon}_r (\omega )= \...
Laurier's user avatar
  • 189
1 vote
2 answers
72 views

Understanding Feynman Diagrams in Loop Corrections to the propagator $\phi ^3 $ theory [closed]

I found other posts talking about the same chapter in the same book, but none of them were exactly about what I am asking here. In Srednicki's chapter 14 (Loop corrections to the propagator), we are ...
Fernando Garcia Cortez's user avatar
0 votes
0 answers
9 views

3 magnetic scalar points along a 1D axis of 1m. Using interpolation, how many additional data points needed for certain accuracy (statistical errors)? [closed]

On outdoor magnetic field surveys we're using a two fluxgate (vertical magnetometer configuration), while walking, spacing 1m. Since we're quite unhappy with our results, we now want place more ...
user387449's user avatar
2 votes
0 answers
41 views

Average force using Heisenberg equation on a bounded particle

My problem states: Prove that the average force that acts on a bounded particle is zero. My question is: How do we represent a bounded particle? I believe that a bounded particle represents a ...
Jorge A. Cortés Dávalos's user avatar
0 votes
0 answers
10 views

Energy range when deriving heat capacity in Sommerfeld model

In my textbook, they assume a scenario in which the thermal energy of electrons is $k_BT << E_F$ , then only electrons which are near the Fermi level could be excited due to external thermal ...
Thành Nguyễn's user avatar
0 votes
2 answers
59 views

Confused about Weinberg's result of gravitational time dilation

I am reading Weinberg's Gravitation and Cosmology. In section 3.5, the author got a result$$\frac{dt}{\Delta t}=(-g_{00})^{-1/2}\tag{3.5.2}.$$Here $dt$ is the time interval of a stationary observer in ...
rioiong's user avatar
  • 611
9 votes
1 answer
913 views

Does the cosmological constant entail a mass for the graviton?

If I consider the Einstein equations into the form $$ R_{\mu\nu}=\kappa \left(T_{\mu\nu}-\frac{1}{2}g_{\mu\nu}T\right)+\Lambda g_{\mu\nu} $$ and then linearize them, we should get by moving to ...
Jon's user avatar
  • 3,950
1 vote
0 answers
49 views

Does gravity accelerate you towards the geodesic of light between you and the mass?

If there's a planet far away, you will accelerate straight towards it due to gravity. If you place a Schwarzschild black hole right in the middle between you and the planet (the distance between the ...
Zach's user avatar
  • 171
0 votes
0 answers
14 views

What would the temperature of the tropics be if the atmosphere did not try to balance out heat the latitudinal surplus and deficit

The atmosphere acts to even out the heat imbalnce between the surplus at the tropics and the deficit at the poles. Assuming that the composition and density of the atmosphere stay the same, what ...
Geoff Parsons's user avatar
0 votes
1 answer
37 views

Argument for relationship between density of states and degrees of freedom and energy

From Reif's Fundamentals of Statistical and Thermal Physics chapter 2.5 Behaviour of the density of states: Can anyone give a clear explanation for why the density of varies rapidly as Energy ($E$) ...
David's user avatar
  • 29
1 vote
0 answers
53 views

Orthogonal complement of null vector [closed]

I am trying to solve excercise 8.5 d) from Straumanns book on general relativity (here V is an n-dimensional Minkowski vector space): Prove that the orthogonal complement of a null vector is an $(n-1)$...
Lenti's user avatar
  • 11

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