Can there by a theory that is both UV and IR stable?

In summary, the question asks if a theory can have a stable RG fixed point in both the UV and IR, and the answer is yes. A concrete example is ##g\phi^4## theory in 3 dimensions, which has 2 fixed points: the free theory at ##g=0## and an interacting theory at ##g\sim 1/3##. The position of the fixed point may be slightly changed by higher loops. By integrating the beta function, we can see that the UV fixed point corresponds to taking the scale to ##\mu \rightarrow \infty##, while the IR fixed point is reached by sending ##\mu\rightarrow 0##.
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metroplex021
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The question is in the title: is it possible for a theory to be both UV and IR stable? And concrete models would be much appreciated!
 
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If you mean: can a theory have a stable RG fixed point in both the UV and IR, the answer is yes. A concrete example is ##g\phi^4## theory in 3 dimensions. The 1-loop beta function for ##g## is

$$ \beta(g) = \frac{1}{16\pi^2} ( - g + 3 g^2).$$

There are 2 fixed points: the free theory at ##g=0## and an interacting theory at ##g\sim 1/3## (higher loops would be expected to change the position slightly). We can integrate the beta function to get

$$ g(\mu) = \frac{ 16\pi^2 g(\Lambda) }{ 48\pi^2 g(\Lambda) - \frac{\mu}{\Lambda} ( g(\Lambda) -1)}.$$

For fixed ##\Lambda##, we see that taking the scale to ##\mu \rightarrow \infty## sends ##g(\mu) \rightarrow 0##, so this fixed point corresponds to the UV. Similarly, sending ##\mu\rightarrow 0## takes us to ##g(\mu)\rightarrow 1/3##, so this is an IR fixed point (generally known as the Wilson-Fisher fixed point).
 
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1. Can you explain what it means for a theory to be both UV and IR stable?

UV and IR stability refer to the behavior of a theory at both high and low energies, respectively. A theory that is UV stable is able to accurately describe physical phenomena at high energies, while a theory that is IR stable is able to accurately describe physical phenomena at low energies.

2. Why is it important for a theory to be both UV and IR stable?

It is important for a theory to be both UV and IR stable because it allows for a more comprehensive understanding of physical phenomena. A theory that is only stable at one energy range may not accurately describe the behavior of physical systems at other energy ranges, limiting its usefulness in explaining a wide range of phenomena.

3. Is it possible for a theory to be both UV and IR stable?

Yes, it is possible for a theory to be both UV and IR stable. In fact, many well-established theories in physics, such as the Standard Model, are both UV and IR stable. However, finding a theory that is stable at all energy ranges is a challenging task and is an ongoing area of research in theoretical physics.

4. How do scientists test for UV and IR stability in a theory?

To test for UV and IR stability, scientists use a combination of mathematical calculations and experimental evidence. Theoretical calculations can predict the behavior of a theory at different energy ranges, and experiments can be conducted to verify these predictions. If a theory accurately describes physical phenomena at both high and low energies, it is considered to be both UV and IR stable.

5. Are there any drawbacks to a theory being both UV and IR stable?

One potential drawback of a theory being both UV and IR stable is that it may become more complex and less elegant. In order to accurately describe physical phenomena at all energy ranges, a theory may need to incorporate many different concepts and equations, making it more difficult to understand and work with. Additionally, some theories that are both UV and IR stable may still have limitations or inconsistencies, which can make them less useful for certain applications.

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