# How to perform a integral in momentum space

• LCSphysicist
In summary, the limits of integration in momentum space are determined by the range of values the momentum can take and can be specified by experimental conditions or theoretical calculations. A definite integral in momentum space has specific limits and yields a numerical result, while an indefinite integral represents a general function. To perform a change of variables, appropriate transformation rules should be used to simplify the integral. Numerical methods, such as Monte Carlo integration, can be used to evaluate integrals in momentum space, but analytically performing the integral may also be possible through techniques such as integration by parts or partial fractions. However, in many cases, numerical methods may be a more practical approach.
LCSphysicist
Homework Statement
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Relevant Equations
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I am not sure how does the integral was did here. More preciselly, How to go from the first line to the second line? Shouldn't it be $$\frac{4 \pi}{(2 \pi)^3} \int _{0} ^{\infty} p^2 e^{ip*r}/(2 E_p)$$ ? (x-y is purelly spatial)

There is a ##\cos(\theta)## in the dot product which brings out the ipr and causes the difference in the exponentials when you integrate over ##d(\cos(\theta))##

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## 1. What is momentum space?

Momentum space is a mathematical representation of physical space that describes the motion and momentum of particles. In this space, each point represents a possible momentum state of a particle.

## 2. How is an integral performed in momentum space?

To perform an integral in momentum space, you need to first define the limits of integration, which correspond to the range of possible momentum values. Then, you need to determine the integrand, which is the function that you are integrating. Finally, you can use mathematical techniques such as substitution or integration by parts to solve the integral.

## 3. What is the purpose of performing an integral in momentum space?

Integrals in momentum space are useful in many areas of physics, including quantum mechanics and statistical mechanics. They allow us to calculate important physical quantities such as energy, momentum, and probability distributions.

## 4. What are some common techniques for performing integrals in momentum space?

Some common techniques for performing integrals in momentum space include Fourier transforms, Laplace transforms, and contour integration. These methods allow us to simplify complex integrals and solve them more easily.

## 5. Are there any limitations to performing integrals in momentum space?

Yes, there are some limitations to performing integrals in momentum space. For example, some integrals may not have closed-form solutions and require numerical methods to be solved. Additionally, the choice of limits and integrand can greatly affect the difficulty of the integral.

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