Is Supersymmetry required by String theory?

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Discussion Overview

The discussion revolves around the role of supersymmetry (SUSY) in string theory, specifically whether it is a necessary component for the theory to be consistent or if string theory can exist without it. The scope includes theoretical implications and interpretations within string theory.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that SUSY is required for the particle spectrum of string theory to be consistent, as its absence could lead to tachyonic particles that are difficult to interpret physically.
  • Another participant argues that non-perturbative formulations of bosonic string-field theory can reinterpret tachyonic states as unstable, suggesting that string theory might not necessarily require SUSY.
  • It is noted that SUSY is the only known method to incorporate fermions into string theory, which are observed in nature, implying a need for SUSY in that context.
  • One participant mentions that the necessity of SUSY may depend on the definitions used for string theory, indicating that a strict definition may affirm its necessity, while a looser definition might allow for string theories without SUSY.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of SUSY in string theory, with some asserting its importance while others suggest it may not be essential under certain definitions or formulations. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

There are limitations regarding the definitions of string theory being used, and the implications of tachyonic states and their interpretations are not fully resolved. The discussion also highlights the dependence on theoretical frameworks and assumptions about the nature of string theory.

TheHeraclitus
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TL;DR
Supersymmetry is often mentioned together with String theory, but do all String theories require it?
From what I understood Supersymmetry means there are more particles than we currently know about and they are predicted by (some/all, I do not know) versions of String theory.
Is it so important to String theory or can it work without SUSY?

Thank you!
 
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Susy is, as far as we know, required for the particle spectrum to be consistent. Without susy you get e.g. tachyonic particles which are hard to interpret as physical particles. So yes.
 
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haushofer said:
Susy is, as far as we know, required for the particle spectrum to be consistent. Without susy you get e.g. tachyonic particles which are hard to interpret as physical particles. So yes.
Non-perturbative formulation of bosonic string-field theory reinterprets tachyonic state as an unstable state, very much like tachyonic Higgs field before symmetry breaking is reinterpreted as an unstable state. By a process of tachyon condenzation the unstable state (local maximum of the potential) settles down into a stable state (local minimum of the potential) and excitations around the stable state are no longer tachyonic. So I would say no.

But we still need susy in string theory because that's the only known way (as fas as I am aware) to incorporate fermions into string theory, and we need fermions because they are observed in nature.
 
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I have seen multiple knowledgeable theoretical physicists state authoritatively that supersymmetry is necessary as a low energy approximation of string theory.

To some extent, however, it boils down to definitions.

If you use a fairly strict definition of string theory or M-theory, then this is probably correct.

If you use a loose definition of string theory that, for example, borrows heavily from its mathematical methods without embracing the entire discipline's canonical form for it, perhaps you could get a stringy theory that doesn't have supersymmetry as a low energy approximation.
 

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