The h Bar

Slereah

15:00

prolly

0celo7

@ChrisWhite Ah, a GR person

Do you agree that the exercises in Sachs-Wu are completely ridiculous?

13.4GB memory used

Is that a new record

@Slereah AHA

In a convex normal neighborhood the exponential map is a diff and thus open

So (2) of Lemma 2 in O'Neil is immediate

And Lemma 3 follows

Slereah

Hm

but what aboot globally, tho

0celo7

You just have to prove that $I^+(0)$ is open

@Slereah That's Lemma 3

Slereah

Aight

So I guess we can agree

Compact spacetime can't be causal

0celo7

oh I was going to write some AMA questions

2

Q: Is this user a sockpuppet?

I wonder how the (bleep) did this answer get "accepted", and looked at the question. The account [redacted] was created and only this one post was ever made.

discussion

lol

6

A: The Time That 2 Masses Will Collide Due To Newtonian Gravity

For completeness, here's an another solution (though not so elegant as Shanth's solution). The equations of motion (from the 2nd Newton's Law) of the two point masses $m_1$ and $m_2$, respectively, are: $$G\frac{m_1 m_2}{(r_2-r_1)^2}=m_1 \ddot{r_1}\Leftrightarrow \ddot{r_1}=G\frac{m_2}{(r_2-r...

$\mathbb d$ o.o

3075

15:11

lol

reminds me I was on narcotic drugs for like 15 days I should get back to doing physics.

0celo7

you're a junkie now

Slereah

Get back on the drugs

0celo7

smokeeeeeeeee

Slereah

Do amphetamines, it is what Erdős recommends

3075

they're only pills, and I have 30 left.

no use for them though.

0celo7

15:13

Sell them to me

3075

I'd give them to you for free but I don't think I can ship them.

0celo7

Cloth shoes: never again. They're getting stained :/

ACuriousMind

Bake them into a cake, then send the cake

0celo7

I wonder if I can wash them

3075

lol that works.

Slereah

15:14

Or don't bake them in but send us a cake, still

0celo7

@Slereah why would you turn down free drugs

ACuriousMind

^

Slereah

Free cake is breddy good

0celo7

@ACuriousMind you ******* junkie

all of you

user116211

Why do you want to eat arbitrary pills @0celo7 o.O

0celo7

15:16

@MAFIA36790 I don't

I'm a law-abiding citizen

3075

but seriously drugs are dangerous, I was on this really strong drug a day after surgery and I was becoming delusional and I thought the nurses were trying to kill me at night.

user116211

hmm.... also nice.

0celo7

I was doing something

Oh the AMA quesitons

ACuriousMind

@3075 That sounds rather terrifying :/

3075

yeah I could barely sleep.

ACuriousMind

15:17

Maybe really just send a cake, then

Secret

It is highly possible no nonsense from me in future chat messages will ever beat that collosal nonsense that I posted a few hours ago

0celo7

@Secret I don't think most of us read that.

I don't read anything over ~5 lines

Even then if it's 5 lines the first 2 better be damn good

Secret

I have not finished my sentence, lol :D

0celo7

@ACuriousMind Did I tell you I worked Mr. Morton into my literature final essay

Secret

therefore whatever incoherent thing Acuriousmind et. al. encountered from me in the future, it should be a lot more comprehensible than anything that ever existed since the dawn of time

0celo7

15:20

...wat

@Secret ...do you always announce things like this or do we get special treatment

ACuriousMind

I think the last known appearance of Mr Morton was your midterm or something

0celo7

@FrancescoS NO

@ACuriousMind I worked him into the final.

ACuriousMind

@0celo7 ??? He hasn't said anything

Secret

I have a tendency to immitate aperture science broadcasting systems

0celo7

The prompt was to sit down a puritan minister and a transcendentalist and get them to agree on something

FrancescoS

15:21

@0celo7 sorry?

0celo7

@ACuriousMind I didn't finish that thought

@FrancescoS This is a GR zone today, no QFT

Secret

and the full itallics give an impression I am talking to some covert party in the background

0celo7

@ACuriousMind and while Morton is not a puritan minister, I worked him in anyway

ACuriousMind

Oh, you're just jealous I might answer other people's questions. Carry on, then :P

0celo7

and the prof liked my essay so much he sent out an email about it

FrancescoS

15:22

@0celo7 Don't worry, let you talk about what you want; I don't care ;)

Secret

which brings into point of another of my tendency: I have a tendency to immitate spy agencies

0celo7

@ACuriousMind implying you've helped me at all today

I like to think I've become more self-sufficient, but you're the judge of that

ACuriousMind

@0celo7 No, I did not imply that...

Secret

@ 0celo7

2 mins ago, by Secret

I have a tendency to immitate aperture science broadcasting systems

0celo7

@Secret ???

@Secret honestly you might have some issue

you say really random stuff

user116211

15:24

nods T__T

0celo7

@ACuriousMind You implied I'm jealous for your attention

Secret

@ 0celo7 Well, as long I am not random when solving problems and responding to correct social context, it will be fine

My mind is an exploding mini big bang, quoting one of my professors

0celo7

Is that the Australian term for ADHD

Secret

9 mins ago, by Secret

It is highly possible no nonsense from me in future chat messages will ever beat that collosal nonsense that I posted a few hours ago

The reaosn I said that is because you guys managed to sent the most flagship of my pet theories into a (temporary?) grave, thus anything that comes after will not be utter nonsense

0celo7

@ACuriousMind Is Milnor's def of cobordism on page 42 equivalent to the standard one

Secret

15:28

and this is indeed what is intended, since I have been frustrated for years how to shot it down

I am so glad I don't have quantum pet theories...

else I will be frown upon by the physicists

0celo7

@ACuriousMind And do you know if $M$ is supposed to be compact here

ACuriousMind

@0celo7 I have no idea what the "standard one" is

0celo7

@ACuriousMind what do you think cobordant means

ACuriousMind

I don't have an opinion on that, I never really needed the notion

0celo7

@ACuriousMind But I thought TQFTs were functors on the category of cobordisms

ACuriousMind

15:33

So?

0celo7

implying you should know what a cobordism is

FrancescoS

@0celo7 why do you think ACuriousMind should know everything?

ACuriousMind

@0celo7 I think that category is much narrower than what one calls in general a "cobordism".,

0celo7

@FrancescoS induction

Secret

http://scholarworks.umass.edu/cgi/viewcontent.cgi?article=1025&context=linguist_faculty_pubs
A prosodic theory of nonconcatenative morphology

Why do linguistics reminds so much of category theory. Is analysing languages a type of category...?

0celo7

15:41

Languages are a category.

Most things are categories

Secret

I see

0celo7

ACM might disagree

Most things you care about are categories.

I think that's correct.

Secret

0

Q: Energy Conservation in Changing Potential Well

If you prepare a particle in a basis state, $|n\rangle$ of an infinite potential well of length $L$, the energy of that state will be $\langle E\rangle = E_n$, with zero variance. If you then instantly increase the width of the particle well by some method to $2L$, this state becomes a superposit...

quantum-mechanics energy-conservation wavefunction wavefunction-collapse

sounds like a time dependent perturbation theory on particle in a box will give us some insights

I am guessing that extra energy has to be supplied or taken away by whatever that expanded the well

Otherwise I cannot do this problem on top of my head, will deal with this later

John Rennie

16:00

@Obliv I just don't respond on these occasions. While it's very tempting to make some cutting comment that never ends well.

@0celo7 It seems a bit harsh to close that. I don't know the answer, so while it may seem obvious to you it isn't obvious to everybody.

0celo7

@JohnRennie It's not obvious.

That's the whole point

You'd have to write a book on it

The answer is in Wald

or at least a partial answer is in Wald

There are about 7 essential GR books and you get no love from me unless you've checked all of them

Slereah

No love unless you perused the 3000 pages for the answer

user116211

^^^^ Note that

user54412

@JohnRennie cf my meta post ;)

0celo7

@ACuriousMind How pretentious is writing $M^n\in\mathsf{ Ob(Man)}$

Is that even acceptable

@Slereah 3000?

MTW is 1200, right?

HE is 400, Straumann is 700, Wald is 400

Slereah

16:08

Well how many pages is HE + MTW + Wald + Straumann + whatever

Errr...

0celo7

O'Neil

Slereah

O'neil

0celo7

BEE

Slereah

Sachs-Wu

Penrose

0celo7

Sachs-Wu has no answers

Just questions.

Slereah

16:09

you need questions before you can have answers

Carroll, I guess

0celo7

Yeah

Zee, Weinberg

Slereah

Duffield

0celo7

For sure.

John Rennie

@ChrisWhite if the sufficient prior research requires reading 0celo7's seven essential GR books then I think we should be lenient :-)

0celo7

@ChrisWhite which meta post?

Slereah

16:10

Springer has a spacetime handbook

I wonder if it's any good

0celo7

can't get a mycopy of it

ACuriousMind

@0celo7 Unless you're specifically going for the category theoretic angle, I'd consider "Let M be a manifold" to be better in all respects.

0celo7

so probably not.

Slereah

amazon.com/dp/3642419917

0celo7

@ACuriousMind Good point, although not even categorical geometers write Ob(Man)

Don't know about category theorists though

Slereah

16:11

I've seen Ob(Man) in AQFT

ACuriousMind

I usually see the Ob omitted, anyway

0celo7

$300, must be good

ACuriousMind

Only noobs write Ob, just like only noobs put hats on their operators ;P

Slereah

I still put hats on my operators and arrows on my vectors

Like a good boy

0celo7

My list of GR books comes out to well over 4,000 pages

user116211

16:12

@JohnRennie Now I could get what 7 denotes in 0celo7 ;|

0celo7

SO GET OUT OF MY FACE UNLESS YOUVE CHECKED ALL OF THEM

Slereah

Oh and Stephani

Stephani is p. important

0celo7

4,700

Throw in that one book on twistors

5,100

And some math books

8,000

Slereah

let's make it an even 10.000

0celo7

Arnold for the action principle

Oh

Abramowitz and Stegun obviously.

Rudin

Slereah

16:14

My favorite GR book, of course

0celo7

PDG handbook

Slereah

amazon.com/Physics-Stargates-Parallel-Universes-Wormhole/dp/…

It has the best cover

PDG doesn't contain a lot of GR

a lil bit of cosmology but that's about it

0celo7

We're probably at 15,000 pages

@JohnRennie unless you have checked all of these books, your question deserves to be closed.

Is it weird that I know how long books are

Slereah

amazon.com/Making-Starships-Stargates-Interstellar-Transport/dp/…

Wait a moment

0celo7

I know HE is 392 pages long

Slereah

16:16

Woodward

0celo7

Give or take

Slereah

Isn't that the crazy guy

0celo7

I have lots of chapters memorized

I know the HE and Wald chapters by heart

Slereah

when you read wormhole stuff, you have to remember the crazy guys

John Rennie

@0celo7 well it would keep the PSE nice and quiet :-)

0celo7

16:18

@JohnRennie well there's not a single good explanation of time dilation in those books

Slereah

Well they are GR books

Not pleb SR

0celo7

I don't even know SR

John Rennie

@0celo7 You need to come to me for that

0celo7

@JohnRennie I might write a correct answer to that one day.

But I'm not very interested right now

Slereah

SR is GR for Minkowski space

obviously

John Rennie

16:20

@0celo7 Another correct answer?

0celo7

@JohnRennie no the correct answer.

In terms of geometry

I'd have to think about it first

Slereah

>thinking before answering

You're not gonna win internet points that way

John Rennie

Was I wrong to close this? My reasoning was that reading the duplicate would teach the OP enough to answer their question. However I'm now wondering if that's fair.

0

Q: Relativity of temperature paradox

The imagined scenario: Part A: From special relativity we know that velocity is a relative physical quantity, that is, it is dependent on the frame of reference of choice. This means that kinetic energy is also relative, but this does not undermine the law of conservation of energy as long as w...

special-relativity statistical-mechanics temperature kinetic-theory doppler-effect

ACuriousMind

@JohnRennie I think there is enough overlap to call it a duplicate - however, the answers to the other question don't seem particularly decided on what the actual answer is.

0celo7

@ACuriousMind My PDE prof hatred linear operators :(

ODE prof didn't

>hatred

*hatted

@ACuriousMind coincidentally the PDE prof is an applied mathematician and the ODE prof is a geometer

Or maybe not coincidentally

Slereah

16:40

Does a geometer build triangles and such

for the triangle shop

0celo7

He's the one who proved the Godel thing

Secret

@ACuriousMind The OP's doppler shift case seemed to align with Einstein and Planck, while the statistical mechanics approach of case b seemed to be aligned with Landsberg. Given that it is obviously a duplicate, but

@JohnRennie Dear Mr Rennie, thanks a lot for the linked post, I had not come across it yet. Regarding the duplicate mark, although there's overlap between the two posts, namely the discussion on whether temperature is relative or not, but my post is rather presenting a concrete scenario and asking questions about it, including how temperature is correctly defined in such circumstances. Moreover, I still don't see the bottom line, so am I to go with case a or b? or both are wrong? Would you mind reconsidering the duplicate mark? — user929304 24 mins ago

1) how to address to the OP politely but completely and explain why it is a duplicate in order to clarify things? and

2) It turns out the issue of temperature is still quite disputed, for temeprature to be defined in the most rigorous way, I am guessing we should always use the themodynamic beta defintion of $\frac{\partial S}{\partial E}$...?

Obliv

the kernel of a group action is different from that of a homomorphism right

David Z

@JohnRennie if the question is a (not necessarily strict) subset of the other one, such that any reasonably complete answer to the other question would also cover this one, then you were right to close the question. Otherwise, you weren't. So I'd say.

John Rennie

@DavidZ I was kind of hoping for a yes/no answer :-)

David Z

16:52

IMO the fact that reading the other question would teach the OP enough to answer their own question does not itself make the question a duplicate, although it is probably correlated with being a duplicate.

John Rennie

@DavidZ OK so the answer is no. I'll withdraw the close vote.

ACuriousMind

@Obliv ...what?

Obliv

defined differently* @acuriousmind

ACuriousMind

There is no such thing as "kernel" of a group action. I'm not sure what you're talking about

Obliv

@acuriousmind crazyproject.wordpress.com/2010/01/20/…

David Z

16:55

@JohnRennie I didn't actually read the question, you know

ACuriousMind

@Obliv Yeah, unless you get me a better reference than a website called "crazyproject", I'm going to go ahead and say "kernel of a group action" is not a commonly used term.

John Rennie

@DavidZ Now he tells me! I've just reopened the question. Oh well, I'll leave it to the jury to decide. If I'm unsure about closing as a duplicate I guess the sensible course is not to close it.

Obliv

the text by dummit & foote called it that

what do you call it

ACuriousMind

That there looks like...the intersection of all stabilizers. I guess it is actually the kernel of the map $G\to\mathrm{Aut}(X)$ that one can get from any group action.

David Z

@JohnRennie eh, I dunno, closing tends to prompt people to edit the questions to improve them so it's not the worst thing

Obliv

17:01

so why is it defined as $\{g \in G~|~ga = a$ for all $a \in A\}$ ? It doesn't define it in the text and I thought it would be defined as $\{(g,a)~|~g\in G~a\in A, ga = I_A\}$ It seemed like the right idea.. @acuriousmind

eh you don't have to answer that I'll just take it for what it is actually

ACuriousMind

@Obliv 1. $ga=I_A$ doesn't make any sense, as $A$ is just a set. 2. What do you mean "why" is it defined like that? It's defined like that because that's what corresponds to the kernel of the group homomorphism $G\to \mathrm{Aut}(A)$.

Obliv

@acuriousmind you said $ga$ is the image of an element of $G\times A$ so I thought it made sense in my mind.

ACuriousMind

...what is $I_A$ supposed to be?

Obliv

identity in the target set $A$

$G\times A \to A$ no?

ACuriousMind

Sets don't have identities.

Secret

17:05

One thing (as a user in PSE in the long past) that often annoys me is when people close questions, they seldom respond why and how it is a duplicate.

It is true that closing a question will prompt the OP to edit their questions, but for some questions, some clarifications might be needed to point them in the correct direction on what need to be edited

And the trouble is, not all of us are as 24/7 as the h barers and some of the users don't even bother to explain the closure

Having said that, I have no idea ho can this be resolved, given that we cannot really control individuals

Obliv

so the kernel doesn't really exist, except to a homomorphism that is precisely the group action? @acuriousmind

ACuriousMind

@Obliv what?

Obliv

okay nevermind

0celo7

If anyone visits my school note that the best toilet on campus is on the 5th floor of the Chemical engineering building

Clean and they have good toilet paper

Secret

are you living in the maths department, given that you are quite mathematical oriented?

(too lazy to dig the chat log for your education background again)

0celo7

17:19

@Secret no

I live in engineering buildings because I am an engineer

Secret

i see

what subfield of engineering have you studied?

0celo7

Nothing yet, I'm in my first year

Secret

I see

0celo7

And I'm not "math-oriented"

I don't even know what a set is

Literally, I don't know what the definition is.

Secret

ok

speaking of engineering, I have a couple uni friends who studied chemical engineering, electrical engineering and renewable energy engineering (such as photovotalics)

They are often very helpful in remind me how to relate my research chemistry to the engineering disciplines

I however, know very little about it, other than chemical engineers always need to deal with a lot of differential equations, and circuit diagram like interfaces in order to ensure the right amount of chemicals were added into the reactor

Slereah

17:33

Sets are a primitive notion

They are not really defined

Only operations on sets are defined

John Rennie

18:12

He's off again!

-1

Q: What are the largest numbers in physics?

In mathematics there are some big numbers such as the busy beaver numbers which are large but have a short description. I was wondering if we allow physical definitions of numbers we can make some bigger ones. So how big is this number (very approximately), assuming we live in a spatially infinit...

physical-constants statistics

Slereah

The largest number and cDonalds Theorem - Look Around You

►

Slereah

18:49

So anyway, what is the largest number in physics

1 (number of universes)

Something more???

0celo7

Where is your number curiousone, i am waiting. nothing? then dont open your mouth — Loffen 35 mins ago

YES

GET REKT

bolbteppa

@0celo7 you don't study math, neither sets nor linear algebra, you don't study physics like SR, yet you study Sobolev spaces in general relativity books, & Sard's theorem in differential topology books, touche

0celo7

@bolbteppa dude I understand linear algebra

That was a year ago

Slereah

I am thinking hard of how to formulate my question on Math Overflow

I don't want to sound like a yahoo

I must think like a mathematician

bolbteppa

:p

0celo7

18:55

What topology are you working with

Are all your operators bounded?

What function space

What is BB(BB(99))

bolbteppa

What bornologies are you using?

Slereah

Topology is $\Bbb R^2$ minus two disks (or squares), identified with [some function i'll write down]

Function space is like

Schwartz

0celo7

That's pretty broad

Slereah

That's usually the function space for scalar fields

0celo7

What's the metric?

Slereah

18:57

Metric of the original space is flat space metric

I'm not sure if Schwartz space is well defined for weird topologies

I know it's not generally defined for some spacetimes

bolbteppa

Weak topology is defined as the topology that makes all functions continuous, so people just say weak topology

Physics Meta

0

Q: The best Question Grand reopening - Gather

my question Large numbers in physics was closed. Two users gave a "reason". The first one didnt make any sense at all. And the second one I have adjusted my question to take care of. So now could we reopen? If not, can I get a reason? I dont get what people have agaisnt my question. I get at fir...

discussion

0celo7

Locally you have a past, a present, a future and a lot of "side-ways". Globally you have a past, a present, a future and a lot of "side-ways". Why do you think that will change? As for time-like curves... I would stay away from that. Absolutely nothing prevents theories from having unphysical solutions and that's what these are. — CuriousOne 29 mins ago

smashes head

so what is a manifold, anyway

Slereah

CuriousOne is the Karl Pilkington of physics

I am a manifold

Of manifold ancestry

ACuriousMind

"the best question grand reopening"...is this a troll?

0celo7

19:00

I've removed some comments that were off topic and/or inappropriate, and their replies. — David Z ♦ 2 hours ago

Abuse!

ACuriousMind

We call that "moderation".

0celo7

@ACuriousMind Maybe we should perform moderation in moderation.

John Rennie

@0celo7 No it isn't. Loffen is being a twit.

0celo7

@JohnRennie That's offensive, please remove it.

John Rennie

@0celo7 Busy beaver number. There's a nice description of them here

Slereah

19:06

computation theory has a lot of big numbers

John Rennie

twit is not an offensive word. Swap the i for an a though ...

Slereah

Although as an ultra finitist, I don't really believe in numbers superior to 53

0celo7

@Slereah 53 is a bit high

I haven't seen 53 in the night sky

@ACuriousMind Do you have access to Guillemin-Pollack

Slereah

what number appears in the sky?

0celo7

69 B)

what is an equivalence relation, anyway

Slereah

19:14

It's a relation

That has the properties of an equivalence

I think it's like

Symmetry

0celo7

lol, apparently bordism is a thing

Slereah

Reflectivity

the third one

0celo7

so a cobordism is the dual of a bordism

Slereah

Errr... transitivity

0celo7

@Slereah transitivity

Slereah

19:15

yeah that one

0celo7

@ACuriousMind Don't you think cobordism is such a nice word?

Slereah

usually with the semantic that "eh I guess that's the same object"

0celo7

> A central insight connecting algebraic topology with mathematical physics is that a strong monoidal functor on a category of cobordisms with values in something like the category Vect (with its standard tensor product of modules) may be thought of as a formalized incarnation of what in physics is called a topological quantum field theory

wipes brow

Slereah

Too much algebra 4 me

0celo7

I just wanted a nice notation for "M and N are cobordant"

Slereah

19:18

$$M \mathfrak{Cobord} N$$

0celo7

time to prove that cobordism is an equivalence relation

oh boy

List of cohomology theories

This is a list of some of the ordinary and generalized (or extraordinary) homology and cohomology theories in algebraic topology that are defined on the categories of CW complexes or spectra. For other sorts of homology theories see the links at the end of this article. == Notation == S = π = S0 is the sphere spectrum. Sn is the spectrum of the n-dimensional sphere SnY = Sn∧Y is the nth suspension of a spectrum Y. [X,Y] is the abelian group of morphisms from the spectrum X to the spectrum Y, given (roughly) as homotopy classes of maps. [X,Y]n = [SnX,Y] [X,Y]* is the graded abelian group given as...

@ACuriousMind A list for you

is it a noob move to write $(N\times[0,\epsilon))\cup (N'\times(1-\epsilon])$

instead of $N\times[0,\epsilon)\cup N'\times(1-\epsilon]$

0celo7

19:50

oh wow $\mathfrak{v}$ is a v

Slereah

Yeah fraktur is kind of shit

0celo7

how do I do piecewise functions in TeX

Slereah

13

Q: piecewise function

So this is a piecewise defined function I have that I need to talk about: f(a,b) = \left\{ \begin{array}{lr} \text{open} & : \text{RMSD}_\text{s-open}\ge6, \text{RMSD}_\text{closed}\ge6\\ \text{closed} & : \text{RMSD}_\text{closed}\le2 \\ \text{semiopen} & : \text{RM...

math-mode

Obliv

Do autistic people usually insult other people? I don't remember if they do

If they don't loffen is a pretty obvious troll. (since he claimed he was autistic in one of his comments)

Oh I'm pretty misinformed. It appears autism is related to more aggressive behavior.

Secret

I am mild asperger, which nowadays is classified as part of the autism spectrum, and I don't recall myself insulting other people, for example

in fact, autism people are best known for their tendency to ignore anything irrelevant to their goal, and I found insulting other people a terribly inefficient thing in terms of getting my answers

0celo7

20:15

So this is why they make up reasons and vote to close? I have autsim I wouldnt understand, it just doesnt make sense to me — Loffen 1 hour ago

haha the best defense

dmckee

The spectrum covers a lot of ground and there is a lot of variation in exact symptoms even among people at comparable points (areas?) on it. I don't claim to be an expert, but I think that some behavior that could be classified as 'persistent' or 'focused' if you were being clinical can come across as aggressive or even hostile to people not used to it.

0celo7

Oh gosh please don't ban me

I'm so sorry

dmckee

Not that I care for the purposes of PSE moderation. Be nice applies even if you don't get it.

0celo7

@Slereah Your thing is in 19 hours

So I'll be busy during it

Lucky!

Slereah

I probably should prepare something

FrancescoS

20:27

In a dijets analysis (for example at LHC), one studies the contributions to $pp\rightarrow jet + jet$ coming from the $uu,du,dd$ valence-quarks initial states because $u\bar{u}$ or $uc$ initial and final states in the Standard Model are highly suppressed. My questions are:

1) How does one reconstruct that the dijets come from these initial states?
2) The SM says processes with $u\bar{u}$ or $uc$ initial states and $u\bar{u}$ or $uc$ final states are suppressed. Why can't we take these processes into account if we suppose it exists another model?

0celo7

>:(((((((((

FrancescoS

For example, look at this paper arxiv.org/abs/1201.6510 at page 4, beginning section 3

ACuriousMind

@FrancescoS I'm not sure we have any regular familiar with these sorts of calculations. @dmckee might be your best bet.

0celo7

@FrancescoS if you've figured out e.g. physics.stackexchange.com/questions/229259/…, you might want to write an answer so future students of the book can find an answer if they get stuck there too

dmckee

I never did collider physics. I did go to a collider summer school one year, but that was circa 15 years ago.

0celo7

20:34

@dmckee and you can't remember?

dmckee

Reconstruct goes the usual way. First generate a clustering analysis to define tracks as either in or out of the jet. Add up the energy (from the calorimeter) and momentum of the tracks that are ruled in and construct a four-vector. Try out all possible combinations of pairings between jets until you know which combination(s) gives reasonable physics and go with those; perhaps assigning a weighting to them.

Both the cluster identification and the combinatorial problem are hard to get exactly right, but good 'mostly right' methods exist.

FrancescoS

@dmckee so, can you understand from which interactions the jets come from?

dmckee

I don't recall anything about the hows and whys of jet flavor surpression.

@FrancescoS You certainly get the mass of the state that gave rise to the jet, which gives you some information but is not always definitive. The rest I don't recall.

FrancescoS

@dmckee ok, thanks you very much

0celo7

@ACuriousMind Why is $\mathrm{GL}(n)^+$ connected?

I'm hoping that's not a stupoid question

continuous maps preserve the number of connected components

Stupoid, as I suspected.

is that even correct

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