# Tag Info

## Hot answers tagged baryogenesis

75

Congratulations on finding a method for baryogenesis that works! Indeed, it's true that if you have a bunch of black holes, then by random chance you'll get an imbalance. And this imbalance will remain even after the black holes evaporate, because the result of the evaporation doesn't depend on the overall baryon number that went into the black hole. Black ...

30

Locality The random walk would be expected to create different (opposing) asymetries in different regions, including regions that are distant enough to not affect each other. If this would be the main cause of asymetry, then we'd expect it to cause a predominance of matter in some areas of the observable universe and a predominance of antimatter in other ...

23

In principle, the number density of photons include all photons, both of cosmic origin (e.g. the cosmic microwave background; CMB) and of astrophysical origin (starlight, gamma rays from gamma-ray bursts, radio waves from quasars, etc.). However, CMB photons outnumber all other types of photons by more than 200:1. The cosmic background radiation The ...

22

Your simulation randomly creates a single particle that is either type 1 or type 2. If these two types are charged, then either of these two creation processes violates conservation of charge. Charge conservation is an absolute law of physics as far as we know, and this includes processes like the formation and evaporation of black holes. The OP clarified ...

14

The matter-antimatter asymmetry requires the three Sakharov conditions to be satisfied. I'll summarise that link's explanation. Unfortunately, your question isn't completely solved. The first condition is that some interactions don't conserve baryon number (I.e. baryons minus antibaryons, baryons being three-quark hadrons such as protons and neutrons). How ...

10

Good question! Regarding (2) baryon number is certainly violated at Planckian energies. If you can make a black hole, you can eat up baryons. Luboš Motl's argument that you linked to is correct in this regard. Whether you can make a believable scenario of quantum gravity driven baryogenesis at the Planck time is up in the air as far as I know. It's the old ...

9

The sphaleron is kind of the opposite of the instanton, and kind of the same. Let's make that statement precise: An instanton is a local minimum of the action that mediates vacuum tunneling (link to an answer of mine how and why instantons do that). The sphaleron sits in-between the vacua, in a certain sense, it is the instanton "in the middle of tunneling":...

8

Short answer: nothing has been seen. Long answer: Questions like this on the experimental limits in particle physics can usually be answered by looking things up in the Particle Data Group's annual Review of Particle Physics. There is a summary online version and an extensive (but free!) print version. EDIT: Here (pdf) is the full section on conservation ...

7

We calculate the free energy (density) for the Higgs field $\phi$ at finite temperature. In the Standard Model, this looks like $\mathcal{F}_{SM}(\phi,T) = -\frac{\pi^2}{90}g_* T^4+V_{SM}(\phi, T) \ ,$ where $g_*$ is the number of degrees of freedom in the SM ($g_*=106.75$). The potential has the form $V_{SM}(\phi,T) = D(T^2-T_0^2)\phi^2 - ET\phi^3+\frac{... 7 To achieve a nonzero baryon asymmetry, one needs to satisfy the so-called Sakharov conditions: Baryon$B$violation C-symmetry violation and CP-symmetry violation Interactions out of thermal equilibrium If at least one of these "asymmetries" or "imbalances" is missing, the total$B$of the Universe will remain zero. The Standard Model preserves$B$... 6 It is a non-perturbative effect because it is 1-loop exact. The triangle diagram is actually the least insightful method to think about this, in my opinion. The core of the matter is the anomaly of the chiral symmetry, which you can also, for example, calculate by the Fujikawa method examining the change of the path integral measure under the chiral ... 5 The interconversion of matter and energy is described by quantum field theory. If you're interested the question What keeps mass from turning into energy? is on this subject. The particular quantum field theory that describes our universe is called the Standard Model, and there are three important symmetries that apply to the standard model - charge ... 5 The LHC depends in large measure on it's huge luminosity for its usefulness. Making anti-proton beams is hard, and making them at high luminosity is harder still. While there are advantages to$p\bar{p}$, they are not overwhelming and the luminosity issue drives all. 4 Every Speck of matter in the world has its anti form basically that we have antimatter whenever we have matter. This is not exact; in theory any form of matter can have its corresponding form of antimatter, but the universe we live in is predominantly made up of matter. This is an experimental observation because when matter meets antimatter there is a ... 4 Yes, you can observe elastic proton-anti-proton scattering. Indeed, the cross section is not all that different from that of elastic proton-proton scattering. The main difference is that$pp$is predominantly elastic at low energy, and dominantly inelastic at high energy, whereas$p\bar{p}$is dominantly inelastic at all energies. Also note that inelastic ... 4 Short answer (we're hung up on terminology): If you use the word "Leptogenesis" exclusively for theories with lepton violating vertices, then "Dirac Leptogenesis" is a misnomer. If you use the word "Leptogenesis" more broadly, to describe theories where leptonic interactions are important for Baryogenesis, then calling it "Dirac Leptogenesis" is OK. Long ... 4 I think your misunderstanding is precisely that you think that$U(1)$gauge symmetry in SM can be associated to any quantum number such as baryon or lepton number. No, it can not. The$U(1)$coming from$SU(3)_C\otimes SU(2)_L\otimes U(1)_Y$is related to a quantum number called hypercharge,$Y$We say that baryon and lepton numbers are symmetries in a '... 4 Matter and antimatter isn't created one at a time at random. To fix your simulation, you'd need to always create an electron at the same time you create a positron. Does adding a black hole break that symmetry? Definitely not. Charge is still conserved - the positron that "falls" into the black hole doesn't just disappear - it alters the charge, angular ... 3 Leaving out numerical factors, we have that $$\mathrm{d}j_A = \mathrm{Tr}(F \wedge F)$$ This already shows that we are dealing with a topological quantity, since the RHS is the second Chern character of the gauge field (or rather, the principal bundle associated to it). Now, there is also the (3D) Chern-Simons form $$\omega = \mathrm{Tr}(F \wedge A - \... 3 Recreating the conditions of the early universe is a popular explanation, not an exact statement of what is happening at the LHC. It was never the primary goal of the LHC to produce anything similar to conditions in the early universe. To whatever extent it does so, that's just a side benefit of the searches for the Higgs boson and supersymmetry. Besides, ... 3 In the Standard Model, the baryon and lepton number are accidental global symmetries. However, they are conserved only at the classical level: quantum corrections do not respect them, i.e., they are anomalous. The interesting thing is that they are violated by exactly the same amount. In terms of currents we write:$$\partial_\mu J_B^\mu=\partial_\mu J_L^\... 3 So, there are several possible ways the universe could be baryon symmetric: A region of the universe where antimatter dominates. There is a problem with this theory, though - 30 years' worth of scientific research has calculated just how far away this type of region would have to be, and from these calculations it is considered very unlikely that any part ... 3 The calculation is actually reasonably simple. Most of the photons in the Universe are CMB photons, and the number density of CMB photons has been measured to exquisite accuracy. There are about$N_\gamma = 4.11\times10^8\,{\rm m}^{-3}$. The mass density of baryons has also been measured, both "directly" via elemental abundances and the Big Bang ... 3 To start, it is important to notice that a statement like "For each x antiquarks, there are x+1 quarks" is vacuous unless you specify the instant at which you are looking at the system. To give an example, if you start with 100 antiquarks for every 101 quark, there will be a time when you'll have 50 for every 51, and finally 0 for every 1. This said, I'd ... 3 Let's look at the expression for the differential decay rate of$X\to f$, where$f$contains an arbitrary number of particles with momenta$\mathbf p_i$and spin$s_i$. This is given by: $$2m_X \text d\Gamma =(2\pi)^4\delta^4(P_X-\sum_i p_i)\vert \mathscr M (X\to f)\vert ^2 \text d \Phi,$$ where the phase space factor$\$\text d \Phi = \prod _i \frac{\text {d}...

3

The comment on the review you indicated can be explained in the following way. Inflation is a period of nearly exponential expansion of the Universe that is required to solve the flatness problem, the horizon problem, ecc.. These cosmological constraints, quite independently on the specific model of inflation (single field inflaton, modified gravity and so ...

3

People do consider the lepton asymmetry, it plays an important role in Leptogenesis. This is the idea that the baryon asymmetry was "born" as a lepton asymmetry, which was transferred to the baryon sector during the EW phase transition. Having said this, the baryon asymmetry is certainly discussed more often. This is because 1) we don't know what the ...

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