Questions tagged [leptogenesis]
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33
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Vacuum Degeneracy of the Standard Model
There are infinite vacua, which are degenerate, in Standard Model (people know this in the context of Sphaleron, Instanton and so on). I'd like to know why there are infinite vacua. I'm glad to ...
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0answers
27 views
Validity of thermal average approximation
I'm following this paper about leptogenesis and heavy sterile neutrinos, and the authors define the thermal average of a general momentum-dependent variable $X(k)$ as:
$$\langle X\rangle=\frac{2}{n_{...
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1answer
43 views
About the recent bounds on the baryon asymmetry
While I'm studying the baryon asymmetry, the ratio of baryons number to the photons number in the universe - some times is called baryon density - $: \eta= n_b/n_\gamma$
I have found many experimental ...
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62 views
B-L violation and Sakharov's first condition
The most common version of Sakharov's first condition that I see is "Baryon number violation." Of course this makes sense because without baryon number violation, you can't start out with a ...
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1answer
35 views
Closed-Time-Path & leptogenesis
I'm trying to reproduce some of the results from this paper by B. Garbrecht but I'm having some difficulties getting his Eq. (110),
$$\mathrm{i} \delta S_{N i j}^{<,>}=\mathrm{i}\delta S_{N i}\...
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9 views
Thermal equilibrium of yukawa couplings and one-flavour approximation in leptogenesis
Considering leptogenesis in the context of type-I seesaw mechanism, we may only use the one-flavour approximation when the dynamics takes place at temperatures larger than $10^12$ GeV, i.e, before the ...
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43 views
Amount CP violation needed
It is widely known that the CP violation provided by the Standard Model ( SM )is insufficient to explain the baryon asymmetry that we observe. However, I never came across any quantitative ...
2
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1answer
93 views
In this example, how can we have CP conservation with C violation?
Consider a simple two-body decay process $X\to Y+Z$ where $X$ is a boson, and $Y,Z$ are fermions. If $C$ is violated, $$\Gamma(X\to Y+Z)\neq \bar{\Gamma}(\bar{X}\to\bar{Y}+\bar{Z}).\tag{1}$$
However, ...
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1answer
59 views
Assumptions for Leptogenesis
In a video by Fermilab's YouTube channel "Can leptogenesis explain why there is something instead of nothing?", host Dr. Lincoln states four assumptions for the theory of leptogenesis. One of them is ...
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3answers
84 views
How does the baryon asymmetry control temperature fluctuations of CMB?
The temperature fluctuations of the Cosmic Microwave Background (CMB) have a sensitive dependence on the quantity of baryon asymmetry of the universe. In fact, analysis of CMB fluctuations is one of ...
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1answer
96 views
Is there a lepton anti-lepton asymmetry?
I dont know is this a stupid question or not but I wanted to ask
We all familiar with the fact that there must be some more baryons w.r.t antibaryons. Since we do not observe any anti-baryons we ...
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3answers
340 views
Can muonic atoms exist?
Would it be possible in the standard model to have atom like systems in which muons (or tauons) take the place of electrons? Why don't we see more of them?
For instance it could be related to some ...
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1answer
130 views
Chemical equilibrium for a $2-2$ scattering and Boltzmann equation in cosmology and astroparticle physics
Definition of chemical equilibrium According to the definition of chemical equilibrium in Wikipedia, it is a situation where the rate of the forward reaction is same as the rate of backward reaction ...
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3answers
120 views
Can the CKM matrix supply the CP asymmetry as required by baryogenesis, in principle?
In the process of Baryogenesis through Leptogenesis from the decay of heavy Majorana neutrinos, the necessary CP violation is perhaps provided only by the CP phases in the PMNS matrix. But the Weak ...
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1answer
155 views
Quantifying the baryon asymmetry requires normalizing the baryon number density w.r.t comoving entropy density or photon density-Why?
This question has been edited a little to clarify the confusion I have.
The matter-antimatter asymmetry of the Universe quantified by the baryon asymmetry as
$$Y_B=\frac{n_B-n_{\bar{B}}}{s}=\frac{n_B}...
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1answer
161 views
Why is the quantum number $\frac{1}{3}B-L_\alpha$ said to conserved in the Standard model rather than $B-L$?
In the standard model, the baryon number $B$ and the lepton number$L$ are conserved perturbatively. However, the B+L quantum number is anomalous and is violated via non-perturbative effects while ...
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3answers
196 views
Number excess of baryons per antibaryon in a comoving volume: Interpreting $Y_{\Delta B}$ in the present epoch
The baryon asymmetry of the Universe is quantified in terms of $$\eta=\frac{n_B-n_{\bar B}}{n_\gamma}|_0= (6.21\pm 0.16)\times 10^{-10}\tag{1}$$ or $$Y_{\Delta B}=\frac{n_B-n_{\bar B}}{s}|_0=(8.75\pm ...
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2answers
260 views
Why does matter-antimatter asymmetry only refer to baryon asymmetry?
Why is the matter-antimatter asymmetry of the Universe quantified by the baryon asymmetry,
$$Y_B=\frac{n_B-n_{\bar{B}}}{s}$$
i.e., the difference in the number densities of baryons $n_B$ and ...
3
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2answers
352 views
How does inflation get rid of initial Baryon asymmetry (if any)?
Why is it said that even if the baryon asymmetry existed as an initial condition, the asymmetry would have been destroyed by inflation. How does inflation get rid of initial Baryon asymmetry (if any)?
...
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0answers
153 views
Consequence of C and CP-violation: What does it ensure and what it does not?
This question is a continuation of one of my earlier posts here and the accepted answer. Consider a two-body hypothetical decay $p^+\to e^+\gamma$ in a quantum field theory (say, a GUT). If the ...
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1answer
688 views
Why are both C and CP violation necessary for baryogenesis?
Sakharov condition states both C and CP violation is necessary for baryogenesis. Now consider, for example, a theory with B-number violating interaction and C-violation. Therefore, if $p\to e^+\gamma$ ...
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2answers
221 views
Understanding the fine-tuning problem related to baryon asymmetry as an initial condition
The reason for not assuming the Baryon asymmetry of the universe as an initial condition is often attributed to the following fine-tuning problem: If the baryon asymmetry had been an initial condition,...
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1answer
232 views
Does Leptogenesis require lepton number violating vertices?
One of the Sakharov condition for Baryogenesis requires Baryon number violating interactions in the theory. However, it is also possible to generate a baryon asymmetry via a lepton asymmetry or ...
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1answer
108 views
Can CP-violation arise due to interference between two tree-level diagrams in a QFT?
In Leptogenesis, CP-asymetry arises due to the interference of the tree-level amplitude $N\rightarrow l_\alpha\phi$ (where $N$ is heavy sterile neutrino, $l_\alpha$ is a lepton flavour, and $\phi$ is ...
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1answer
4k views
Does the number density of photons $n_\gamma\approx 10^8 \:\mathrm m^{-3}$ refer to CMB photons only?
When we talk about the present-day number density of photons ($n_\gamma\approx 10^8 \:\mathrm m^{-3}$) in the universe do we mean the number density of CMB photons? I mean there are other sources of ...
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1answer
594 views
How exactly sphaleron transitions erase initial baryon asymmetry, if any?
The sphaleron interactions in the Standard Model (SM) is $(B-L)$ conserving and $(B+L)$ violating. Each sphaleron transition causes the change in the baryon number $\Delta B$ and the lepton number $\...
2
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1answer
220 views
Phase transition and effect on leptogenesis
What is the effect on leptogenesis in the standard model if the electroweak phase transition is (i) first order and (ii) second order?
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1answer
2k views
Difference between instantons and sphalerons
What is the difference between instantons and sphalerons? If they are different, how do they violate baryon and lepton number in the standard electroweak theory?
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2answers
299 views
Baryogenesis via Leptogenesis
Baryon number is directly violated through electroweak anomaly and so does the Lepton number, for each transition from one vacuum to another. The two violations are of equal amount $\Delta B=\Delta L=...
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4answers
3k views
Temperature of electroweak phase transition
How does one estimate the temperature at which electroweak phase transition (EWPT) occurred? Somewhere I have read it is around 100GeV but the reason was not explained.
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2answers
379 views
Sakharov condition of departure from equilibrium
I have a doubt with the third Sakharov condition which demands a departure from equilibrium. But why is that necessary when both baryon violating interactions and well as CP violation is present in a ...
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1answer
277 views
Singlet neutrinos decaying to Higgs bosons during leptogenesis
(i) The Lagrangian of electroweak model extended with right-chiral singlet neutrinos $N_{iR}$ contains the Yukawa coupling term+ the bare Majorana mass term $$f_{\alpha i}\overline{l_{L\alpha}}\hat\...
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1answer
707 views
Why is baryon or lepton violation in standard model is a non-perturbative effect?
The baryon number B or lepton number L violation in the standard model arise from triangle anomaly. Right? Triangle diagrams are perturbative diagrams. Then why the B or L violation in Standard model ...