Particle physics is the study of the fundamental forces of nature as they are embodied in the interactions of elementary and composite particles at high energies and short time and distance scales.
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Accelerating particles to speeds infinitesimally close to the speed of light?
I'm in a freshmen level physics class now, so I don't know much, but something I heard today intrigued me. My TA was talking about how at the research facility he worked at, they were able to ...
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Why do neutrons repel each other?
I can understand why 2 protons will repel each other, because they're both positive. But there isn't a neutral charge is there? So why do neutrons repel (do they even or Have I been misinformed?)
...
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ATLAS Higgs Interpretation
I came across this abstract, and I am curious as to what the ATLAS Team has actually discovered:
Abstract Motivated by the result of the Higgs boson candidates at LEP with a mass of about ...
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What are the details around the origin of the string theory?
It is well-known even among the lay public (thanks to popular books) that string theory first arose in the field of strong interactions where certain scattering amplitudes had properties that could be ...
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Higgs Boson mass in Electron volts?
Im no physics genius here, I was just interested in the Higgs Boson so I was reading this article : How the Discovery of the Higgs Boson Could Break Physics
I came across this
Furthermore, ...
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Why is stringless supergravity not considered by many to be a candidate theory of quantum gravity?
This paper seems to show that $d=4, N=8$ supergravity is finite. Yet the paper only has three citations in spires, and I certainly haven't heard talk of a new candidate theory of gravity.
Why ...
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Mathematics of AdS/CFT
To date, what is the most mathematically precise formulation of the AdS/CFT correspondence, and what are the most robust tests of the conjecture?
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3answers
3k views
Why you need a graviton when you have the higgs boson?
Since I studied General Relativity I had this question running on my mind. As I see it (just taking lectures of Quantum Field Theory right now)
"Why you need a gauge boson for gravity when the higgs ...
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987 views
What are the alternatives to the Higgs mechanism?
Can someone summarize, with references if possible, all of the alternatives to the simplest model (that requires only a single scalar Higgs field with the Mexican Hat potential) of spontaneous ...
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434 views
Hawking radiation and quark confinement
The simple picture of Hawking radiation is that a pair-antiparticle pair is produced near the event horizon, then one falls into the black hole while the other escapes. Suppose the particles are ...
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127 views
What is the 'bump' near $M_{\mu\mu}\approx 30\text{ GeV}$
In this (attached) Summer 2011 plot from CMS (twiki page), they have a plot of the dimuon invariant mass spectrum across 3 orders of magnitude in energy. There seems to be a 'bump' near ...
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287 views
What does the latest $B_s^0\rightarrow \mu^+\mu^-$ results mean for SUSY?
A paper from the LHCb collaboration just came out last week, stating basically that the $B_s^0\rightarrow\mu^+\mu^-$ decay matches standard model predictions, and people are already shouting that SUSY ...
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Phase shifts in scattering theory
I have been studying scattering theory in Sakurai's quantum mechanics. The phase shift in scattering theory has been a major conceptual and computational stumbling block for me.
How (if at all) does ...
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762 views
Decay of massless particles
We don't normally consider the possibility that massless particles could undergo radioactive decay. There are elementary arguments that make it sound implausible. (A bunch of the following is ...
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803 views
115 GeV, 170 GeV, and the noncommutative standard model
Several years ago, noncommutative geometry was used to describe the standard model, somehow yielding a prediction of 170 GeV for the mass of the Higgs boson, a prediction which was falsified a few ...
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200 views
Is there any way to distinguish experimentally gauge mediation from gravity mediation in an unambiguous way?
There are lots of models of gravity mediated SUSY breaking with various spectra as well as various general gauge mediation models. Are there any "smoking gun" experimental singnatures that could ...
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How does the Higgs mechanism work?
I'm not a particle physicist, but I did manage to get through the Feynman lectures without getting too lost.
Is there a way to explain how the Higgs field works, in a way that people like me might ...
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What would happen if you put your hand in front of the 7 TeV beam at LHC?
Some speculation here:
http://www.youtube.com/watch?v=_NMqPT6oKJ8
Is there a possibility it would pass 'undetected' through your hand, or is it certain death?
Can you conclude it to be vital, or ...
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Where does matter come from?
I admit, it's been a few years since I've studied physics, but the following question came to me when I was listening to a talk by Lawrence Krauss.
Is there any knowledge of from where matter that ...
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449 views
“Slightly off-shell”?
I'm not new to QFT, yet there are some matters which are quite puzzling to me. I often come across the statement that real particles (the ones we actually measure in experiments, not virtual ones) are ...
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Do anti-photons exist?
I know what anti-matter is and how when it collides with matter both are annihilated. However, what about anti-photons? Are there such things as anti-photons?
I initially thought the idea ...
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2k views
What does the discovery of the Higgs Boson mean for physics?
Will this unite some theories, or cause some other change in physics, and perhaps our undertanding of the universe?
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878 views
What does it mean that the neutral pion is a mixture of quarks?
The quark composition of the neutral pion ($\pi^0$) is $\frac{u\bar{u} - d\bar{d}}{\sqrt{2}}$. What does this actually mean?
I think it's bizarre that a particle doesn't have a definite composition. ...
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813 views
Is there an accepted analogy/conceptual aid for the Higgs field?
Is there an accepted analogy / conceptual aid for the Higgs field?
In Physics there are many accepted conceptual aids such as
* Schrödinger's cat
* Maxwell's Demon
* I'm sure I'm missing ...
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465 views
What are bootstraps?
I've heard occasional mentions of the term "bootstraps" in connection with the S Matrix. I believe it applies to an old approach that was tried in the 1960s, whereby - well I'm not sure - but it ...
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How come neutrons in a nucleus don't decay?
I know outside a nucleus, neutrons are unstable and they have half life of about 15 minutes. But when they are together with protons inside the nucleus, they are stable. How does that happen?
I got ...
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trying to understand Bose-Einstein Condensate (BEC)
I am a computer scientist interested in network theory. I have come across the Bose-Einstein Condensate (BEC) because of its connections to complex networks. What I know about condensation is the ...
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What's the difference between inclusive and exclusive decays?
For example, why is the semileptonic $B$ decay $B \to X\ell\nu$ inclusive?
I can't find any definition of these frequently used terms, strange.
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30 views
Dual Pairs in Four Dimensions
Following the conversation here, I am wondering if anyone knows of an example of dual pair with 4-dimensional N=1 SUSY which relates a non-Abelian gauge theory on one side to a theory with a ...
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704 views
What happens to matter in a standard model with zero Higgs VEV?
Suppose you reset the parameters of the standard model so that the Higgs field average value is zero in the vacuum, what would happen to standard matter?
If the fundamental fermions go from a finite ...
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327 views
Alejandro Rivero's correspondence: diquarks and mesons as superpartners of quarks and leptons
The idea of “hadronic supersymmetry” originated in the mid-1960s and derives from the observation that baryons and mesons have similar Regge slopes, as if antiquarks and diquarks are superpartners. ...
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222 views
What dark matter can AMS currently find (or exclude)?
The rumor mill is running again, this time it's about the AMS experiment (Alpha Magnetic Spectrometer) that's going to make a major announcement soon.
I suppose they are looking for peaks in gamma ...
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232 views
Neutrino Oscillations and Conservation of Momentum
I would like to better understand how neutrino oscillations are consistent with conservation of momentum because I'm encountering some conceptual difficulties when thinking about it. I do have a ...
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547 views
ATLAS and CMS calorimeters
I was reading this interesting recent review on arxiv about particle identification:
Particle Identification
In figure 2, there is an interesting comparison between the CMS and ATLAS calorimeter ...
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What happens in electron-electron collisions?
What are the results of high energy electron electron collisions? Are other particles created?
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168 views
Derivation of the effective potential between a quark and an anti-quark
Typically in particle physics books (not in QFT books!) I have often seen this statement that the potential between a heavy quark and its anti-quark can be "empirically" represented as $V(r) = ...
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259 views
Does the ruling out of TeV scale SUSY breaking disfavor grand unification?
One of the arguments in favor of TeV scale SUSY breaking is that it leads to the appropriate running of the gauge coupling strengths leading to grand unification, i.e. $k_Y = \frac{5}{3}$ instead of ...
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537 views
Cross-section in relativistic limit: Fermi's golden rule still valid?
In order to calculate the cross-section of an interaction process the following formula is often used for first approximations:
$$
\sigma = \frac {2\pi} {\hbar\,v_i} \left| ...
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infrared free QED and Higgsless standard model phenomenology
This is one of those "what if" fantasy world type questions. I like hard sci-fi so please no "well, you changed one thing about the world so now anything goes." :)
What if the Higgs had no vev?
That ...
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Higgs boson and string theory
Assuming Higgs is found at 125 GeV.Is there any direct or indirect consequence on string theory ? Will it be a blow to string theory or models employing string theory ?
...
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305 views
Do current models of particle physics explain the chemical properties of elements/compounds?
I have a particle system of seven protons and seven (or sometimes eight) neutrons (each formed by their appropriate quarks, etc.) bound together in a state that can be macroscopically described as a ...
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597 views
How do $\pi^0$ particles exist?
I have been taught that the $\pi^0$ particle contains either an up quark and an anti-up quark or a down and an anti-down. How can these exist without annihilating?
Also, it is its own antiparticle, ...
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594 views
Why do physicists believe that particles are pointlike?
String theory gives physicists reason to believe that particles are 1-dimensional strings because the theory has a purpose - unifying gravity with the gauge theories.
So why is it that it's popular ...
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494 views
How are Monte Carlo simulations used in experimental high energy physics?
How are Monte Carlo simulations used in experimental high energy physics? Particularly in studying detectors limitations (efficiencies?) and data analysis.
I will appreciate giving a simple example ...
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392 views
Why muonium is unstable?
This question is closely related to my previous question Bound states in QED.
Muonium is a system of electron and anti-muon. This article in wikipedia claims that muonium is unstable.
QUESTION: Why ...
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984 views
Is it pions or gluons that mediate the strong force between nucleons?
From my recent experience teaching high school students I've found that they are taught that the strong force between nucleons is mediated by virtual-pion exchange, whereas between quarks it's gluons. ...
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471 views
Why are “heavier” particles harder to detect than “lighter” ones?
Something I have read multiple times that I've never intuitively understood is that "heavier" particles are harder to detect than "lighter" ones... For example, I quote from Stephen Hawking's "The ...
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224 views
Bound states in QCD: Why only bound states of 2 or 3 quarks and not more?
Why when people/textbooks talk about strong interaction, they talk only about bound states of 2 or 3 quarks to form baryons and mesons?
Does the strong interaction allow bound states of more than 3 ...
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330 views
Could LEP II have discovered a 125GeV Higgs?
LEP II eliminated the Higgs up to 114.5GeV. If it had been run for longer could it have detected a Higgs at 125GeV?
I Googled for this without any luck, though I did find a comment that LEP II topped ...
