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In the strong coupling limit of type IIA and heterotic E8 string theory, we get 11 dimensional M-theory in which we have no strings. Instead, we have M2 branes.
Are there any other backgrounds in string theory which can't be described by first quantized string theory?
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It might sound stupid but seriously I couldn't find why?
We have a mass with a constant speed, which is acted on by a unit force which is always at right angles to its direction of motion.
Why do the mass travels a circular path!?
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Will the scale say I weigh more, less, or the same on a carpet as compared to a hard floor?
You can assume the scale works via spring mechanism. Free body diagrams encouraged!
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I need a book dealing in particular with the intermolecular forces and, if possible, the diffusive processes. Someone knows an appropriate one?
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The mystery of the mass of the top being in the electroweak scale can be justified by the Higgs mechanism itself; in some sense the top mass is the only "natural" mass, the other masses of fermions being protected by some unknown mechanism so that they are "zero" relative to the electroweak: the typical values of the Y... |
In one dimension -
How can one prove that the Hamiltonian and the parity operator commute in the case where the potential is symmetric (an even function)?
i.e. that $[H, P] = 0$ for $V(x)=V(-x)$
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Seeing this as an academic community, I hope this question is on-topic. Academia is still a long way from beta :(
I have a few questions about reading journal papers in the field of engineering/applied physics.
How do you keep and schedule a reading list?
From the more recent papers, how do you track down the one (or ... |
Hey guys, I'm having a problem in understanding the 1st Law of Thermodynamics.
If i would increase the pressure of a closed system by compressing a gas in a cylinder isothermal, the 1.Law states, that all the work i put in to the system, i get out by heat.
So my 2.state would be the gas at the same temperature (same in... |
Quantum decoherence is an irreversible process which is the result of interaction of the system with its environment. It prevents interference due to lack of coherence. Environment acts just like a heat bath. Now my question is, is the different branches of the wave function of the universe becoming gradually more and ... |
With the dawning of the private space industry, if someone was to build a rocket-based craft that powers you up and then glides in for a landing, what would be the quickest you could get across the Atlantic? Or half way around the world?
(Assume a typical flight trajectory - e.g. don't go through the earth or travel a... |
I'm given with the following problem - it's an easy one, but it's nearly 1AM, I'm tired and I need some push into the general direction to get the solution:
A particle is assumed to be in the state
$\left(-\sqrt{1 \over 3} Y_1^0(\theta, \phi), -\sqrt{2 \over 3} Y_1^1(\theta, \phi)\right)^T$
$Y$ are spherical harmonics.... |
So I am working on my assignment, and have a question about converting coordinates. I dont know whether I should ask here or the math SE, so lets give it a try here.
The force in question is $$\vec{F} = -k\,r^{-n}\,\hat{r}$$
I know the conversion equations but I have no idea how to do it. I need to split the $\hat{r}$... |
What is actual meaning of singularity can we use this term for conclusion in any research paper( related to cosmological models ).what r the types .
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Big Bang theory is widely accepted theory when it comes to origin of universe. What other really compelling theories are out there explaining/supporting the origin of universe. I know many people don't believe in Big Bang theory for various reasons.
Update
Question was not complete before for some reason.
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What are the weak hypercharge and weak isospin quantum numbers of the helicity states of the $W^\pm$ and $Z^0$ bosons?
The W boson is a spin-1 massless particle. Consequently it has three helicity states, negative (left-handed), positive (right-handed), and neutral. As discussed in this paper, these states restrict whi... |
Calculations of the shear viscosity of the quark-gluon plasma (QGP), observed in heavy ions collisions, are performed via the AdS/CFT correspondence [ref1]. One finds that the shear viscosity of the CFT, on the boundary of an AdS spacetime with a black hole in its interior, is equal to the shear viscosity of the fluid ... |
Currently the sun is launching some intense solar flares.
http://www.guardian.co.uk/science/2011/feb/17/solar-flares-northern-lights-uk
Th article I've linked also mentions how a "coronal mass ejection knocked out the power grid in Quebec" in 1989. Some powerful stuff. Thankfully the Earth's magnetic fields protect us ... |
In mechanical engineering, the torque due to a couple is given by $\tau = P\times d$, where $\tau$ is the resulting couple, $P~$ is one of the force vectors in the couple and $d$ is the arm of the couple. A couple is made up of two forces of the same magnitude.
On the other hand, a moment is also given by $M = P\times ... |
In our aerodynamics class we recently discussed the concept of static and dynamic pressure and discussed their application to aircraft instruments. However, I do not understand properly how the altimeter can work.
First of all a small recap of Bernoulli's law. The total pressure is given by $p_t = \frac{1}{2} \rho V^2 ... |
I understand water boils at different temperatures depending on altitude.
I am seeking to get an illustrative explanation for this, including a diagram if possible.
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I am interested in finding out whether the term 'Internal Energy' can be used in both of the following cases:
In the case of a macroscopic body upon which light is incident, the internal energy would designate the total energy absorbed by the body, causing it to heat up (in the absence of other heating mechanisms)
In ... |
Been studying hopping conduction and something that everyone is taking for granted is bothering me.
Let's say we have a bunch of sites that are either unoccupied, singly occupied, or doubly occupied. Due to on-site Coulomb repulsion the two electron levels are separated by U energy at a doubly occupied site. Now everyo... |
Power spectra, coherence spectra, and linear transfer functions are ubiquitous tools of experimental physics. However, our instruments often retain small nonlinear effects which can contaminate measurements. It appears that higher order spectra, in particular the bispectrum, would be ideal tools to investigate nonline... |
I am not someone specialized on physics, I am just curious on why our Body Electrical Resistance measure as shown by a multimeter varies so much.
When allocating the 2 probes each on one hand, the resistance varies from low 100k's of Ohms up to 700k Ohms and even more.
Can someone illustrate in a easy way for a physics... |
Modern theories of interactions in particle physics are gauge ones. I know how the gauge fields are introduced in equations ($D = \partial + A$). I just do not see any physical motivation in it. I am afraid it is done by analogy with QED and that's it. I conclude that it is not the only possible way of description of i... |
A thought experiment: Imagine the Sun is suddenly removed. We wouldn't notice a difference for 8 minutes, because that's how long light takes to get from the Sun's surface to Earth.
However, what about the Sun's gravitational effect? If gravity propagates at the speed of light, for 8 minutes the Earth will continue to... |
As a photon leaves a strong gravitational field, it loses energy and redshifts. Is the exchange in potential energy of a photon characterized by energy quanta?
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Is all particles moving and forever?
Can the movement of particles be stoped ?
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Feynman says in his book "QED" that the square root of the fine structure constant is the probability for a charged particle to emit a photon. But for which wavelength? Or is it an average over all wavelengths?
Note: I meant virtual photon, and I meant a stable charged particle, like the electron. One way to rephrase ... |
Did anyone ever heard about this?I've never seen any serious physicist talk about "mass fluctuations".
Here is the man in his own words: http://www.intalek.com/Index/Projects/Research/woodward1.pdf
And what about this guy: http://aetherwavetheory.blogspot.com/
He claims his theory can explain virtually every unsolved p... |
I would be glad if someone can explain to me the argument as to why supersymmetry breaking is necessarily accompanied by appearance of a massless fermion, namely the goldstino. (and also why this is a non-perturbative effect)
Let me quote here the two lines from the third volume of the QFT books by Weinberg where he t... |
This question was prompted by another question about a paper by Woodward (not mine). IMO Mach's principle
is very problematic (?wrong) thinking. Mach was obviously influenced by Leibniz. Empty space solutions in GR would result in a Minkowski metric and would suggest no inertia.
Mach's principle seems incompatible with... |
For 4 real SUSY generators, the superspace formalism has been worked out a long time ago. For 8 real SUSY generators, some brilliant theoreticians have worked out the details of harmonic superspace. The major surprise is we have to enlarge superspace by taking the product with $S^2$. When we go down to the original sup... |
At this website:
http://heasarc.gsfc.nasa.gov/docs/swift/analysis/threads/uvot_thread_afterglows.html
The passage at the bottom states that a V-band magnitude of 17.62, with an error $\pm$0.02 is a 49.4-$\sigma$ detection significance.
How is this value calculated? Could you provide the working? I have a similar proble... |
Are strange metals -- metallic states that are not describable by the traditional theory of metals (Landau's Fermi liquid theory) -- described by a quantum critical theory?
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What does it take to become a top physicist?
Why do so many extremely talented young upstarts totally flop as they move to more advanced physics?
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This year, the racetrack at Daytona has been repaved. The track was always faster than other tracks NASCAR raced at and several cars in a "train" were faster than single cars or smaller trains. This year is different, however, because two car groups are by far the faster than any other groupings. When a third car jo... |
Assume an observer sent a beam of photons close to an event horizon, say at some distance x (a distance far enough to avoid the photons falling in.) This light would still be observable, albeit red shifted and with it's path curved appropriately. Now assume the black hole absorbs enough mass to expand it's event horizo... |
How do you effectively study physics? How does one read a physics book instead or just staring at it for hours?
(Apologies in advance if the question is ill-posed or too subjective in its current form to meet the requirements of the FAQ; I'd certainly appreciate any suggestions for its modification if need be.)
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In this question, I would love to hear some independent opinions on an issue I asked Juan Maldacena, Nathan Berkovits, Dan Jafferis, and others, but all the physicists may be missing something. The question has 2 main parts:
Is there a dual superconformal symmetry in 2+1-dimensional ABJM theories? In what limit does i... |
Free field theories are definitely local in.
In the interaction picture, we can decompose the fields into creation operator modes and annihilation operator modes. The product of operators can be regulated to finiteness by Wick ordering. In Wick ordering, all creation operators are moved to the left of all annihilation ... |
This question has its origin to the reference on the Aegis experiment at CERN where they aim to produce super cooled antihydrogen and detect whether its reaction to gravity is negative.
It set me thinking that the beams in the Tevatron circulate for more than a second and everything falls about 4.9 meters in a second, ... |
I first saw this on Top Gear, and assumed it was a load of rubbish, but today I tried it out and it actually works, if you walk away from the car continuously unlocking/locking it until it stops, and go a bit further away so that the car will not un/lock. Then out the car keys next to your head and point them directly ... |
It is well accepted that quantum theory has well adapted itself to the requirements of special relativity. Quantum field theories are perfect examples of this peaceful coexistence. However I sometimes tend to feel little uneasy about some aspects. Consider an EPR pair of particles light years apart. Suppose there are 2... |
I'm begining to study Quantization of field with the second quantization formalism. I've studied phononic field, electromagnetic field in the vacuum and a generic relativistical scalar field.
I asked to me if is possible doing the same thing with the Gravitational Field Hamiltonian.
I've heard that we can do it only ... |
If I wander outside in cold weather for 10-20 minutes my body accumulates charges. I get electric shock if I touch metal, e.g., door knob, car door etc.
Now I've two questions:
Why does human body accumulate charges in cold weather?
What can I do to discharge my body without getting the shock?
Thanks for your time.
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There are some interactions that are forbidden by conservation laws, e.g. an electron cannot turn into a positron by conservation of charge and a photon cannot turn into a positron electron pair by conservation of momentum.
My question is if every interaction (between say up to 3 or 4 particles) that is consistent with... |
One reason superstring theory has often been touted as being an improvement over bosonic string theory is that we can impose GSO projections to remove the tachyonic mode. If we insist upon the no tachyon condition, we are left with only five superstring theories.
But what if we don't mind tachyonic modes? After all, th... |
For some very special cases of string compactification backgrounds, we get mysterious enhanced gauge symmetries. What is their physical meaning, and why do they arise? Is there any geometrical interpretation for the enhanced gauge symmetries?
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The solar neutrino problem has been "solved" by discovering that neutrinos have mass and they oscillate. So how accurate are now our predictions about the number and types of solar neutrinos that reach the earth?
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Let us take the standard QED ($e^-, e^+, \gamma$) as a model of QFT and ask what is its "short-distance" physics?
They say the UV infinities appear because we do not know the real physics of short distances and initially we introduce it wrong. OK, but after renormalizations, what physics does remain? Do we replace the... |
I've just moved into my first place, and for reasons I do not condone or recommend I don't have any method of refrigeration right now. Luckily I now live very close to shops, so it isn't a big deal, but it made me think: if I really had to, what would be the most efficient way to keep food cool without using any electr... |
At room temperature....
How long will the sugar stay suspended once dissolved ?
What governs the rate of settling ?
What part does Brownian motion play ?
Sugar might be a bad example...please substitute as needed.
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Very often the energy released in large-scale events (e.g., earthquakes, meteor impacts, etc) is described in terms of some number of 'tons of TNT'. This may be all well and good for those with an intuitive sense of big explosions, but specifically, how many joules are there in the 'ton of TNT'? I can work out how many... |
Classically, shot noise observed in the signal generated by a laser incident on a photodiode is explained as being due to the quantization of light into photons, giving rise to a Poisson process. In quantum optics, on the other hand, the shot noise is said to arise from interference with the vacuum field, which leaks ... |
I would like a tool which allows me to enter some paper citation, and then will begin drawing a graph, where each paper is linked to other papers that cite the original paper or are cited by it.
It seems like this would be a handy way to identify influential papers in a field at a glance.
Does anything like this al... |
I require only a simple answer. One sentence is enough... (It's for high school physics)
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Magnetic fields are obvious distortions.. of.. something, but what exactly are they distortions of? Massive objects produce curvatures/gradients in space-time resulting in what we observe as gravity.. what is the equivalent explanation for magnetic/electric fields?
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When a lambda particle decays into proton and a pion, I am told it does not conserve parity. Why?
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What I mean is could it turn out that the world is not described by string theory / M-Theory, but that nevertheless some version of one of these extra-dimensional theories is true?
I have no real background in this area. I just read Randall and Sundrum's 1999 paper "A Large Mass Hierarchy from a Small Extra Dimension"... |
Below is a picture of a simple pendulum clock. Suppose that the bob (a rigid disk) on the end of the pendulum can spin without friction about its geometrical axis and is spinning at an angular velocity $\omega=const$. Will the clock gain or lose time compared to the ordinary pendulum clock. Or it does not have any effe... |
Why is there a consistent theory of continuum mechanics in which one just consider things like differential elements and apply Newtons laws? Is there a deeper reason for it. Is it the nature of newtonian framework that makes it happen or is it somehow related to nature of bodies (topological spaces with borel measure e... |
In all examples that I know, tachyons are described by scalar fields. I was wondering why you can't have a tachyon with spin 1. If this spinning tachyon were to condense to a vacuum, the vacuum wouldn't be Lorentz invariant---seems exotic but not a-priori inconsistent. Is there some stronger consistency requirement whi... |
http://upload.wikimedia.org/wikipedia/commons/1/1f/Feynmann_Diagram_Gluon_Radiation.svg
Why is the arrow of the positron not upwards?
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For example for an isolated system the energy $E$ is conserved. But then any function of energy, (like $E^2,\sin E,\frac{ln|E|}{E^{42}}$ e.t.c.)
is conserved too. Therefore one can make up infinitely many conserved quantities just by using the conservation of energy.
Why then one can usually hear of "system having $N$ ... |
How do objects dock in space?
There's a recent piece of news that Keppler would dock to the ISS sometime this week. I want to know the operational aspects of it - considering the velocity of the objects involved and also the lack of references.
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I'd like to be able to determine the angular acceleration of a system of two rotating masses, which are connected so as to have a variable mechanical advantage between the two. My background with mechanics went as far as a course in statics, so I'm not sure how to proceed with this.
If I have a single mass of some sha... |
I've been looking for questions about dark matter, and I've read some very interesting answers. However, I desire too look into it deeply.
This is not actually a question. I'm asking the community to recommend interesting references to understanding dark matter and dark energy.
I accept all sort of references: notes,... |
Can you suggest some references for rigorous treatment of thermodynamics? I want things like reversibility, equilibrium to be clearly defined in terms of the basic assumptions of the framework.
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Let's say we have one black hole that formed through the collapse of hydrogen gas and another that formed through the collapse of anti-hydrogen gas. What happens when they collide? Do they (1) coalesce into a single black hole or do they (2) "annihilate" into radiation?
One would expect (1) to be the case if the No Hai... |
In the center of our milky way, it is assumed that a black hole exists with a mass of $\approx 4\times 10^6$ times our sun's mass. How much light bending (in degrees) would arise for stars that are in perspective near the position of this black hole in the sky?
Could the mass of a black holes become so great that it ac... |
Here in this picture
you can see $I_W$ which is induced by H.
But why $I_W$ is not vice versa?
Because of
$$rot \, \vec B = \mu_0 \, \left( \varepsilon_0 \frac{\partial \vec{E}}{\partial t} + \vec j \right)$$ ?
Maybe I have to use
$$\oint \vec{E}\cdot \, d\vec{r} = - \int \frac{\partial \vec{B}}{\partial t}\cdot \, d\... |
Are there any open source tools for calculating the normal modes of arbitrary objects? Input would be some 3D design format and material properties, output would be movement direction and magnitude for each vertex along with frequency of each normal mode.
Commercial software such as SYSNOISE does this.
Failing that, ca... |
What is meant by an "inclined magnetic field"? How is it different from the usual magnetic field?
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According to $a = v^2/R$, the circular velocity and radial distance between two attracting objects (such as planets), must remain in perfect proportion in order for orbital motion to take place. How is it possible for objects in nature to achieve this proportion perfectly?
Not only that, to maintain an orbit seems to b... |
It is well known that the Lagrangian of a classical free particle equal to kinetic energy. This statement can be derived from some basic assumptions about the symmetries of the space-time. Is there any similar reasoning (eg. symmetry based or geometrical) why the Lagrangian of a classical system is equal kinetic energy... |
I am trying to understand graphene as a topological insulator.
The spin orbital interaction in graphene is very small (~10mK?). But if we consider that, then graphene should be a topological insulator. And at the edge electrons should move in opposite direction according to their spin as shown in the figure for graphen... |
I have the following setup:
A <---- wire ----> B
$V_b - V_a = \Delta v = \text{a positive value}$
I have two questions:
Which end of the wire has a higher potential?
What is the direction of the electric field inside the wire?
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Let the $i=x,y,z$ components of the angular momentum have the commutation relations with the supersymmetry generators (also called supercharges?) $Q_a$ ($a = \pm \frac{1}{2}$) as, $[J_i , Q_a] = -\frac{1}{2} (\sigma _i )_{ab}Q_b$. Now if I want to calculate the $J^2$ eigenvalue of $Q_a$ then I might have thought of do... |
I have been reading the stackexchange questions on enhanced symmetries in string theory, the Leech lattice, monstrous moonshine, etc. , and I have a question to ask.
An astute commentator pointed out with enhanced symmetries, massless vector bosons have to couple in the Yang-Mills fashion. Only if the massless vectors ... |
The mass of an elementary particle in string theory is related with the way the string vibrates. The more frantically a string vibrates the more energy it posses and hence the more massive it is. My question is how is the electric charge of a particle is described in S.T. How is the opposite charges described? More spe... |
I'd like to make a comparison of prices, availability and properties of semiconductor substrate layers like Si, Ge, GaP, AlN etc. I wonder what are the problems related to getting such data, what are the leading companies that sell such things, what's the quality, waiting time and so on. I'm not going to buy one, It's ... |
Electricity takes the path of least resistance!
Is this statement correct?
If so, why is it the case? If there are two paths available, and one, for example, has a resistor, why would the current run through the other path only, and not both?
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Actually I have few questions. The answer to a question related to string field theory helped me, but let me still ask it as its probably a bit different.
When e.g we do bosonic/super string theory we see that the vacuum is $|o,p>$ that is not a true space time vacuua (I mean a unique |0>) (depends on CM momenta of str... |
In solving different problems in string theory and also in brane theory, we consider this static gauge choice and I think that's due to the local symmetry (Repara. Inv. (RI) and Weyl) that we have in our world sheet. So, suppose I start with strings and with a general world sheet metric (and some doable ST metric). Onc... |
When we observe at close to the cosmological horizon (as close as we currently can) we see the universe as a much younger, denser place. As we feel the gravitational forces from these objects distant, will we measure a tidal force increasing the distance between an object less distant than the cosmological horizon and ... |
Hopf algebra is nice object full of structure (a bialgebra with an antipode). To get some idea what it looks like, group itself is a Hopf algebra, considered over a field with one element ;) usual multiplication, diagonal comultiplication, obvious units and inverse for the antipode. For a less pathological example, a g... |
Suppose a very long railway line goes from South Africa to Sweden, and
then it's decided to move the entire railway line, sliding it 1 km to the north (leaving aside the difficulty of moving and the force required).
Would the railway bend because of Coriolis force?
I mean, every point of the railway would have differen... |
This question is kind of inspired in this one:
Diff(M) as a gauge group and local observables in theories with gravity
The conundrum i'm trying to understand is how is derived the (quite) extraordinary statement that in GR there are no local observables. I just want to stress that this is indeed an extraordinarily coun... |
What is the full text (and possibly the source) of the summary of the 3 laws of thermodynamics that goes something along the lines of "Can't break even, can't win and can't even stop playing the game"?
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I know that light (or electromagnetic radiation in general) attenuates in intensity as the square of the distance it travels.
Why does it attenuate?
Are the photons being scattered by the medium they pass through?
I also know that the energy carried by light quanta is a function of their frequency only.
If the ans... |
Newton tried to do it with three laws/statements. While the first can be derived from the second, the three form a pretty nice framework.
Later on, I've encountered Lagrangian Mechanics, which involves, from what I gather, one statement:
Objects seek a path that minimizes total action.
Which, while sort of simple, d... |
There might be none. But I was thinking of links between number theory and physics, and this would seem like an example that would definitely solidify that link.
Are there any known natural systems, or physical systems in general (possibly designed), that test the primality of a number directly using the laws of physi... |
Are there any applications of quantum information theory to physics?
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Why do we get information about position and momentum when we go to different representations. Why is momentum, which was related to time derivative of position in classical physics, now in QM just a different representation brought about by some unitary transformation. Is Ehrenfest's theorem the only link?
I just star... |
Let suppose you roll a die, and it falls into a hidden place, for example under furniture.
Then although the experiment has already been made (the die already has a number to show), that value can not be known, so the experiment was not fully realized.
Then till you see the die's top side, the probability remain p = 1/... |
How do you derive Noether's theorem when the action combines chiral, antichiral, and full superspace?
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What is Fermi surface and why is this concept so useful in metals research?
Particularly, I can somewhat appreciate the Fermi energy idea - the radius of Fermi surface which is a sphere. But is there any quantitative use of more complicated Fermi surfaces?
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Reading this PE question
can-we-transport-energy-over-infinite-distances-through-vacuum-using-light, a related question arises naturally:
Is energy transported (by light)? -- (I did believed in this answer until now)
or energy is already 'in site' (vacuum) just expecting to be excited by the photons?
This news insinu... |
In deep inelastic scattering, you describe a collision using the variables $Q^2 = -q^2$ (probe virtuality) and $x = Q^2/2p\cdot q$ (Bjorken x, parton momentum fraction). Now, I seem to remember reading somewhere that in the infinite momentum frame, one of these variables primarily depends on momentum in the transverse ... |
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