Renormalisation of the Fermionic triangle loop

In summary, the conversation discusses the renormalization of a loop diagram in the Standard Model using the Feynman rules. The amplitude is written in terms of external Higgs and loop momenta, and the fermion mass. After evaluating the loop integral functions using dimensional regularization, the expression is found to be divergent. The conversation then mentions the need for counter-terms to make the amplitude finite, and references Srednicki's book for further information.
  • #1
Ramtin123
22
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I am trying to renormalise the following loop diagram in the Standard Model:
Fermionic_triangle.png

Using the Feynman rules, we can write the amplitude as follows:
$$ \Gamma_f \sim - tr \int \frac{i}{\displaystyle{\not}\ell -m_f}
\frac{i^2}{(\displaystyle{\not}\ell+ \displaystyle{\not}k -m_f)^2}
\frac{d^4 \ell}{(2 \pi)^4} $$
where ##k## and ##\ell## are external Higgs and loop momenta, and ##m_f## being the fermion mass. I have ignored the coefficients coming from vertex factors.
After evaluating the loop integral functions using dimensional regularisation, I ended up with the following expression:
$$ \Gamma_f \sim \frac{m_f}{4 \pi^2}
\left( 3\Delta -6\ln \frac{m_f}{\mu} +4
-6 \sqrt{1-4x} \ \ln \frac{1 +\sqrt{1-4x}}{2\sqrt{x}} \right)$$
The loop integral is clearly divergent due to ##\Delta \equiv \ln \pi - \gamma_E + 2/\epsilon## term, when ##\epsilon = 4 -d \to 0##.
Here, ##x \equiv (m_f/k)^2##, ##d## is dimension, ##\mu## regularisation scale, and ##\gamma_E## being Euler-Mascheroni constant.
How should I introduce the counter-terms to make the expression for the amplitude finite?
 
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  • #2
As always in the books.
Check Srednicki.
 
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Likes vanhees71

What is renormalisation in the context of the Fermionic triangle loop?

Renormalisation is a mathematical technique used in quantum field theory to account for the effects of virtual particles in calculations. In the context of the Fermionic triangle loop, it is used to remove divergences and make the calculation of physical observables more accurate.

Why is renormalisation necessary for the Fermionic triangle loop?

The Fermionic triangle loop is a quantum field theory diagram that involves virtual particles, which can lead to divergent integrals when calculated. Renormalisation is necessary to remove these divergences and make the results of the calculation physically meaningful.

What is the process of renormalisation for the Fermionic triangle loop?

The process of renormalisation for the Fermionic triangle loop involves subtracting the divergent terms from the original integral and replacing them with counterterms, which are chosen to cancel out the divergences. This results in a finite and physically meaningful value for the integral.

What are the challenges of renormalisation for the Fermionic triangle loop?

One of the main challenges of renormalisation for the Fermionic triangle loop is choosing the appropriate counterterms to cancel out the divergences. This requires careful calculations and understanding of the underlying theory. Additionally, the process of renormalisation can be time-consuming and computationally intensive.

What are the implications of renormalisation for the Fermionic triangle loop in terms of physical predictions?

Renormalisation plays a crucial role in making accurate physical predictions for the Fermionic triangle loop. Without renormalisation, the results of the calculation would be infinite and meaningless. By removing the divergences, renormalisation allows for more precise predictions of physical observables, which can then be compared to experimental data.

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