Supersymetry versus Anti Particles?

[shrey07]

What is the difference between an anti particle and a super-partner?

Would SIMPs fall under the supersymmetry theory, or the anti particle theory, or both?

 

[ohwilleke]

SHORT ANSWER

Antiparticles have nothing to do with superpartners.

Antiparticles are real known particles related to non-antimatter particles (and the distinction between what we call regular matter and what we call antimatter is mostly an arbitrary distinction made because our universe has much more regular matter than antimatter in it). Antiparticle differ in charge and parity from regular particles but are otherwise identical to their regular matter counterparts.

Superpartners are a hypothetical kind of particles never observed in real life that are supposed to exist in beyond the Standard Model theories called supersymmetry theories.

The only thing that antimatter particles and superpartner particles have in common is that almost all fundamental particles in the Standard Model have an antimatter counterpart, and almost all fundamental particles in the Standard Model in supersymmetry theories have a superpartner counterpart.

SIMPs have nothing to do with either antiparticles or superpartners. They are a hypothetical kind of dark matter that is not normally expected to arise in most supersymmetry theories.

LONG ANSWER

What is the difference between an anti particle and a super-partner?

An anti-particle is a particle identical to an ordinary versions of a particle, but with opposite electromagnetic charge, strong force color charge (if any), parity (i.e. left-handedness v. right-handedness), and spins of the same magnitude but the opposite sign.

These definitely exist and are observed routinely.

They are the CPT (i.e. charge, parity, time) symmetry conserving mirrors of ordinary particles.

The most well known antiparticle is the positron, which is an anti-electron. It has electromagnetic charge +1, the same mass as an electron, and when it is created (usually in an electron-positron pair) the opposite "direction" spin from its electron partner (i.e. the sum of the spins of the electron-positron pair is zero).

When a new quark is created, a new anti-quark must also be created to keep the total number of quarks minus anti-quarks constant (this quantity is called baryon number). When a lepton (i.e. electron, muon, tau lepton, or neutrino) is created, a new anti-lepton must also be created to keep the total number of leptons minus anti-leptons constant (this quantity is called lepton number).

In the Standard Model, all quarks and leptons have anti-particles, W bosons, and all composite particles made of quarks bound by gluons. There is no observable difference between the properties of a photon or a Higgs boson or a Z boson and its hypothetical antiparticle - they are their own antiparticles. The situation with gluons is a bit more involved.

A superpartner is a concept from supersymmetry theory (a.k.a. SUSY). Supersymmetry theory is an extension of the Standard Model of Particle physics that assumes that there is a special kind of symmetry between fermions (i.e. fundamental particles with spin-1/2 like quarks and leptons) that we normally think of as "matter", and bosons (i.e. fundamental particles with spin-0, spin-1, or spin-2 like photons, gluons, W bosons, Z bosons, Higgs bosons and hypothetical gravitons) which we normally think of as force carrying particles.

Supersymmetry has been popular among theoretical physicists, despite the fact that no affirmative observational evidence supports it, because it would resolve a number of mathematical puzzles found in the Standard Model of Particle Physics, because it is easier to do some kinds of calculations with because it is more symmetric, and because it is widely described by people familiar with string theory as something that should be present as a low energy approximation of any viable version of string theory (although I've never seen a rigorous proof of that conventional wisdom about string theory).

In the most minimal version of SUSY, every fundamental Standard Model fermion has a particle (called a sparticle) which is a spin-0 boson as a counterpart, and every fundamental Standard Model boson has a particle (called a sparticle) which is a spin-1/2 fermion as a counterpart (except the gravitino counterpart to the hypothetical graviton which is spin-3/2).

Supersymmetry theories also, generically, have additional Higgs bosons (usually at least four, two charged, one electrically neutral with even parity but a different mass than the Standard Model Higgs boson and one with odd parity), since supersymmetry theories generally have at least "two Higgs doublets").

Due to particles with identical quantum numbers blending into mixtures of each other and the extra Higgs bosons, the correspondence of sparticles to Standard Model fundamental particles is not quite one to one (most notably the neutralino and the chargino). A list of them can be found, for example, https://gravity.wikia.org/wiki/List_of_particles#Hypothetical_particles.

In non-minimal supersymmetry theories there can be more than one superpartner for each ordinary Standard Model particle, and there can be more than four extra Higgs bosons.

Sparticles have antiparticles of themselves just as their corresponding ordinary particles do.

Superpartners and all extra Higgs bosons are strictly hypothetical. None have ever been observed. There are only masses for which particular types of superpartners are excluded by high energy physics experiments. A collection of those exclusion ranges can be found here. In general, experimental evidence has established that if superpartners and extra Higgs bosons exist at all, that they have masses much greater than their Standard Model particle counterparts (with the possible exception of one electrically neutral extra Higgs boson).

Would SIMPs fall under the supersymmetry theory, or the anti particle theory, or both?

Neither.

A SIMP (strongly interacting massive particle) is a hypothetical dark matter candidate that interacts strongly with other SIMPs but weakly with ordinary matter. It is basically an extreme version of self-interacting dark matter. It is often envisioned that multiple SIMPS combine to form a composite dark matter particle analogous to ordinary matter hadrons such as protons and neutrons (which are composite particles made of quarks bound to each other by gluons).

SIMPS have nothing to do with anti-particles (although they could have anti-particles depending upon the properties assigned to particular versions of these hypothetical particles).

One of the main motivations for SIMP dark matter particles is that they could help resolve problems that more traditional dark matter candidates have had fitting the observational evidence at galaxy scales (like the discrepancy between the theoretically predicted shape of inferred dark matter halos in galaxies with traditional WIMP cold dark matter and the observed dark matter halo shapes that are inferred from how stars in galaxies actually move).

SIMPs are also not a very obvious dark matter candidate in supersymmetry theories.

Instead, the WIMP (weakly interacting massive particle) is the hypothetical dark matter candidate most closely associated with supersymmetry theories.

Supersymmetry theories usually assume that the lightest supersymmetric particle (i.e. the lightest sparticle) a.k.a. LSP, is stable due to "R-parity" conservation (which basically assumes that supersymmetric particles can't decay to ordinary matter) and that this LSP constitutes WIMP dark matter. SUSY theories assume this because, just as in the Standard Model where more massive fundamental particles decay rapidly into lighter fundamental particles, more massive fundamental superpartners are assumed to decay rapidly into less massive superpartners. This would leave only the lightest supersymmetric particles as stable, long lived particles, which is a property that most dark matter candidates need to have to fit observations of phenomena attributed to dark matter.

But all or most of the parameters space of supersymmetric WIMP dark matter candidates from minimal supersymmetry theories (i.e. almost all WIMP candidates with particular masses and other properties) has been ruled out by direct dark matter detection experiments and by other means.

 

[arivero]

Antiparticles have nothing to do with superpartners

Well, perhaps it is about having the same mass.

 

[ohwilleke]

Well, perhaps it is about having the same mass.

Of course, we know based upon observational evidence that superpartners of ordinary particles in supersymmetry theories, if they exist, do not have the same mass as their ordinary matter partners. And that antiparticles have exactly the same masses as their ordinary particle counterparts, by theory, and confirmed by observation to all but very small uncertainties of the same magnitude as the uncertainty of the ordinary particle mass measurements.

So superpartners and antiparticles definitely have different masses if superpartners exist, with some possible exceptions for the superpartners of gravitons and non-Standard Model Higgs bosons, all of which are themselves hypothetical and have never been directly observed.

This is because the most massive fundamental particle is the top quark (at 173 GeV +/-) and bosonic superpartners of quarks are all excluded for masses significantly in excess of 173 GeV, while bosonic superpartners of leptons are likewise excluded for masses in excess of the most massive Standard Model lepton, the tau lepton (which has a mass of about 1.776 GeV).

Likewise, the moss massive known ordinary matter particle that is a boson is the Higgs boson at 125 GeV, and fermionic superpartners of massive Standard Model bosons are all excluded for masses in excess of 125 GeV. Similarly, fermionic superpartners of zero mass Standard Model bosons are excluded for masses in excess of zero (with the arguable exception of the gravitino superpartner of the hypothetical graviton, which isn't strongly bonded.).

 

[arivero]

Of course, we know based upon observational evidence that superpartners of ordinary particles in supersymmetry theories, if they exist, do not have the same mass as their ordinary matter partners. And that antiparticles have exactly the same masses as their ordinary particle counterparts

Yep, it is interesting. It is all about symmetry breaking. SUSY can be broken in a very general way, while CPT can not really be broken deeply, it "breaks" only by going from zero mass to yukawa mass.