The h Bar

Brandon Enright

12:00 AM

Well today was 166 reputation. My most yet!

ManishEarth

:)

ManishEarth

12:14 AM

time to sleep

Brandon Enright

@ManishEarth g'night!

David Zaslavsky

3:13 AM

@BrandonEnright enough of his answers included what I would consider misinformation that I didn't trust him

2

Brandon Enright

@DavidZaslavsky do you have (and are you willing to provide) an example? Many of his answers were way over my head so I had no way of evaluating them.

He definitely approached problems from a unique and sometimes controversial perspective.

David Zaslavsky

hm... well it's been a while so I don't remember one off the top of my head, but I'll let you know if I find one

Brandon Enright

Yeah I'd definitely be interested next time you run across one.

David Zaslavsky

IMO unique and controversial are not virtues in their own right

Brandon Enright

I agree however I like to be driven to surprising lines of reasoning.

For example I read the whole description of kickstarter.com/projects/1811478489/… for the shear entertainment factor :-)

@DavidZaslavsky I'll definitely concede though that he was a caustic personality that stifled disagreement and steamrolled people.

I'm amazed how many perfectly good answers dmckee leaves as questions.

Leaves as comments rather.

David Zaslavsky

3:29 AM

A lot of people seem to do that, actually. I guess when you're writing an answer you can always think of what else you would put in it if you had time, and it makes you more likely to see your own answers as inadequate to be posted as answers

nonagon

8:10 AM

Please have a look here :

0

Q: Work Done by Tension

http://www.picamatic.com/view/9198898_Screen_Shot_2013-05-03_at_12.44.41_PM/ http://www.picamatic.com/view/9198901_Screen_Shot_2013-05-03_at_12.44.58_PM/ At an instant , this is the situation , velocity in horizontal direction is $0$, gravity acts vertically downwards and tension acts horizonta...

nonagon

11:40 AM

Because tension is there in horizontal direction , and it acts for a however small but finite amount of time , hence , since a=F/m , and for a small time it acts , hence it must increase velocity by a x t. where t is the time for which it acts and F here is tension and m is mass of the ball/stone which is rotating in circular path
Kindly see the edit too
And if only tension is there , then acc. to Work Kinetic Energy theorem , the Kinetic energy must not change , hence forth , speed must not change , but it is changing here according to newton's laws

a*t means a x t .

Crazy Buddy

1:16 PM

@007 You'd better post that in MSO - a pre-poll on what others think ;-)

@ChrisWhite What about me? It was me who triggered the topic..! :D

@ManishEarth The mortarboard is only once - even for mods no matter how good they're..! :P

Crazy Buddy

1:34 PM

Okay, this is a feedback on the effects that SE had on me..!

I've got two questions..!

1) Have I improved in my English skills (I think you may all know how crazy I was (in my English) when I joined here...)

nonagon

3:13 PM

007 ?

you ol?

007

4:12 PM

@nonagon ?

nonagon

4:35 PM

@007 Can you help with Tension problem I have posted ?

Brandon Enright

9:53 PM

@dmckee I think I found a good answer for Chris's Neutrino vs Photo race question in the form of this paper: arxiv.org/abs/1109.6562

And in this blog post about the paper: profmattstrassler.com/articles-and-posts/…

One of the questions I have about the paper involves the sentence "As in all cases of superluminal propagation, certain otherwise forbidden processes are kinematically permitted, even in vacuum.". It seems like the paper is about neutrinos exceeding the speed of light in whatever medium they're in, and not limited to the vacuum.

It seems to me though the speed of light through the earth would be extremely slow compared to a vacuum just like the speed of light is so slow in water. If that were the case we would have expected the opera results for the neutrons to be way slower than the speed of light, accounting for their cherenkov radiation in the rock.

dmckee

10:48 PM

@BrandonEnright I've only skimmed the preprint, but I'm pretty sure that "superluminal" in that quote means faster than the speed of light in vacuum.

Brandon Enright

Yeah reading through it, it seems that way too however matt strassler's blog entry emphasizes "Specifically, if a neutrino could travel faster than electrons could travel, then with sufficient energy the neutrino could emit an electron and a positron."

dmckee

It is also worth recalling that Minos has a measurement of \delta = v_\nu - c = (10ish \pm 5ish) \times 10-^{-5}.

You'll note that the central value there is also sumerluminal, but at only 2 sigma it is simply assumed to be a statistical artifact.

Brandon Enright

yeah the paper I linked to uses some icecube results to get the error to within 10^{-11}

or rather the excess above c

dmckee

I am---in my profound ignorance---a little concerned about "the flavors all have the same speed" arguments. It goes to the same question you were asking yesterday, and there is not complete treatment thatI'm aware of.

Boris told me he was almost done with e NLO calculation but that it was harder than he expected.

Brandon Enright

Yeah I'd still really like to understand why the three waves stay linked and don't spread out in space

Your diagram in one of the answers had "entanglement" listed but I didn't really understand what the argument was for keeping the states together

dmckee

10:56 PM

That argument is not so much that the sates are kept together as that they remain coherent until the next interaction, which is a slightly different thing.

It's the same reason you have to allow the electron to go through both slits---you don't know which type it "is".

Is in scare quotes because in a real sense it is all allowed types.

Brandon Enright

Is my understanding that the three neutrinos that propagate are "constant mass" neutrinos and are a mix of three flavors and the three "constant flavor" type neutrinos are a mix of the three mass types?

dmckee

Here's a paper he wrote subsequent to my talk with him: inspirehep.net/record/1118840?ln=en

Brandon Enright

In some sort of strange 3x3 matrix

dmckee

How comfortable are you with the standard QM treatment of position basis versus momentum basis?

The neutrino mixing matrix is more of the same, but in a more abstract space.

Brandon Enright

@dmckee hardly at all unfortunately

I'm somewhat familiar with digital signal processing so I'm somewhat comfortable with amplitude domain versus frequency domain and I tend to use that mental analogy for position versus momentum

dmckee

11:04 PM

Getting used to the idea that there can be equally real, but non-equivalent ways of describing a state---and understand how measurements can results in changes in those different basis is the big hurdle.

When the neutrino is created or detected it most do so in one of the flavor states.

But when it travels it is evaluated in the mass basis.

The flavor states each correspond to a mixture of mass states (and vice versa).

So, you establish a particular flavor when you make it. Translate that into a mixture of mass states, which you allow to propograte (all separately and coherently), and when you get to the detector all three of the mass states are converted into mixtures of flavor states and added together before the probability of detection is computed for each possible flavor.

Brandon Enright

So all that's changing with propagation is the probabilities but the mass is staying constant while propagating?

dmckee

I exhibit some of the math here, but I don't know how much it will help you.

Brandon Enright

With regard to the initial flavor, it's my understanding that the flavor is dependent on conserving lepton number. So if a reaction produces an electron it needs to produce an electron anti-neutrino. Then when that propagates it can be measured later as a different flavor. Doesn't that violate lepton number?

dmckee

@BrandonEnright It has all three masses while it propogates. Just like the electron goes through both slits. Sorry, that's how the math works.

@BrandonEnright It violates the lepton-flavor numbers (two of them, natch) but not the global lepton number. Unless neutrinos are Majorana particles in which case it could do both.

Isn't the weak interaction fun?

Brandon Enright

Yeah I thought the whole point of neutrino (at least why they were proposed initially) was to preserve those numbers.

Turns out neutrinos do exist, only to violate those numbers later

dmckee

11:13 PM

Neutrinos were proposed to save the conservation of momentum.

Lepton numbers came later.

Brandon Enright

Gotcha. That actually makes more sense.

I read this answer regarding the math and flavor basis a few days ago but the math is still a bit over my head.

Regarding the three mass states being a mix of flavors and the three flavors being a mix of masses. Once all of the details of the mixing matrix are worked out / measured and the math is able to make oscillation prediction that match experiment, does that mean it's basically impossible to add a 4th neutrino flavor that participates in the mixing? It would have to be a sterile neutrino or some other non-participating neutrino?

So far I'm able to follow this Boris Kayser paper. That may be a first for me with QM papers :-)

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