I am currently involved in the study of various dark matter models that aim to accommodate both cosmological and collider data simultaneously. **The microscopic world is indeed very connected to cosmology**, and both actually speak with each other.

_{[image credits: Gtsourdinis (CC BY-SA 4.0)]}

In a [**recent article**](http://arxiv.org/abs/1810.07224), I have investigated, together with my collaborators, a specific class of models [**extending the Standard Model of particle physics**](https://steemit.com/science/@lemouth/why-going-beyond-the-standard-model-of-particle-physics). Those models, called **LND models**, feature dark matter, are motivated by the unification of the fundamental interactions and additionally fix several other limitations of the Standard Model, like the [**masses of the neutrinos**](https://steemit.com/science/@lemouth/the-chameleons-of-the-standard-model-neutrinos-in-a-nutshell). In terms of dark matter, they in fact exhibit an option that is generally thought of as non reasonable with respect to existing data. Moreover, although this option is currently allowed by data, the dark matter experiments of the next decade will be able to fully rule it out, together with the future results of the [**Large Hadron Collider**](https://home.cern/topics/large-hadron-collider), the LHC at CERN. ___ ## GOING BEYOND THE STANDARDS: SUPERSYMMETRY ___ Although highly tested for decades, the [**Standard Model of particle physics**](https://steemit.com/steemstem/@lemouth/some-thoughts-about-stem-on-steem-bonus-a-complete-introduction-to-particle-physics) is [**incomplete**](https://steemit.com/science/@lemouth/why-going-beyond-the-standard-model-of-particle-physics) and should be extended. This is the core reason why new phenomena in particle physics are expected: one needs **a solution to the conceptual issues and practical limitations of the Standard Model**. [**Supersymmetry**](https://steemit.com/science/@lemouth/new-phenomena-in-particle-physics-searching-for-our-dear-susy-aka-supersymmetry) consists in one of these, solving several problems of the Standard Model in one shot.

_{[image credits: CERN]}

Supersymmetry is a potential symmetry of nature in which each of the Standard Model particles is connected to partners of different [**spin**](https://en.wikipedia.org/wiki/Spin_(physics)), also known as **superpartners**. I recall that the spin is a property of any particle and consists in its intrinsic [**angular momentum**](https://en.wikipedia.org/wiki/Angular_momentum). I will not spend much time on superymmetry (please see [**here**](https://steemit.com/science/@lemouth/new-phenomena-in-particle-physics-searching-for-our-dear-susy-aka-supersymmetry) for more information), but I will instead solely mention that **the most minimal supersymmetric theory brings already a lot**. Supersymmetry first **stabilizes the Higgs boson with respect to quantum corrections** (the microscopic world is quantum). The masses of the Higgs boson and the mediators of the fundamental interactions are what they are, and this makes the Standard Model very un-natural as its parameters must be tuned up to their 30^th decimal to avoid issues. The presence of the superpartners allows one to automatically kill any issue brought by the corresponding Standard Model particle. Moreover, the lightest superpartner can in general be a potential candidate for explaining the problematics of **dark matter** and many supersymmetric models feature the grand **unification of all fundamental interactions**. ___ ## LND SUPERSYMMETRY: GIVING UP MINIMALITY BUT NOT UNIFICATION ___ Supersymmetry has however not been found so far, so that it may be hiding better than originally thought of. One potential reason is that most searches for supersymmetry assume that it is minimal (all superpartners are those shown below).

![](http://www.steemimg.com/images/2017/01/18/Susy-particles5c57e.jpg) _{[image credits: CERN (but cannot find where anymore)]}

However, **why should nature be minimal**? Whilst **minimality is elegant**, there is no good reason behind it. In [**my work**](http://arxiv.org/abs/1810.07224), we have investigated one supersymmetric option where **one gives up minimality whilst preserving the unification of the fundamental interactions**. It is called LND supersymmetry, as the model particle content is extended by new heavy **Leptons, Neutrinos and Down-type quarks**. Existing data does not allow to extend the model arbitrarily. However, LND supersymmetry offers us a way to do so in a way explaining why we have not observed anything at the LHC, but also why **neutrinos are massive** (that is one of the shortcomings of minimal supersymmetry). And here comes dark matter: LND supersymmetry turns out to be additionally compatible with cosmology. ___ ## LND DARK MATTER ___ Standard cosmology features that the dynamics of the universe is ruled by [**dark matter**](https://steemit.com/steemstem/@lemouth/dark-matter-from-its-origins-to-its-freeze-out).

_{[image credits: Maxwell Hamilton (CC BY 2.0)]}

Dark matter is an **invisible substance that interacts gravitationally**. It explains the circular motion of stars around the galactic centers with [**classical mechanics**](https://en.wikipedia.org/wiki/Classical_mechanics), the properties of the [**cosmic microwave background**](https://arxiv.org/abs/1502.01589) (the radiation left over from the big bang), the [**formation of the large structures in the universe**](https://arxiv.org/abs/astro-ph/0307212) and much more. But **dark matter has not been observed so far**, even if it consists in the most hunted stuff of the universe. LND supersymmetry features **more than 3 neutrinos**, which is necessary to explain the masses of the neutrinos. All of those new neutrinos however have superpartners, so that the lightest of them could potentially be a novel option for dark matter that is weird enough to have escaped detection up to now. ___ ## TAKE-HOME MESSAGE - SNEUTRINO DARK MATTER ___ In the LND model we studied, we have abandoned minimality. It is not only allowed by data but we can also explain why neutrinos are massive. In the LND setup, this is however done in a way preserving the unification of all fundamental interactions. One of the consequent LND novelties is that we can have sneutrino dark matter, where sneutrinos are the supersymmetric partners of the neutrinos. This consists in the main difference with other scenarios: in general, sneutrino dark matter is excluded by the observations. In our work, we have shown that LND sneutrino dark matter is allowed. We can both **reproduce the measured dark matter abundance in the universe and explain why dark matter has not been observed in direct detection experiments and in cosmic rays**. We have also demonstrated that LND sneutrino dark matter will be deeply probed within the next 10 years thanks to the expected advances in dark matter experiments. Another fun fact is that the LND model also features an extra charged lepton (a fat big brother of the electron) that could be more or less easily found at the LHC. In other words, this model is appealing because it provides an explanation to current data and is as well testable on a very short term. In a few words, **it will either be discovered or excluded**. ### STEEMSTEM ### SteemSTEM aims to build a community of science lovers to make Steem a better place for Science Technology Engineering and Mathematics (STEM). We have recently released our [**own app, steemstem.io**](https://www.steemstem.io/#!//@steemstem/it-s-time-for-stem-to-have-its-own-home-on-steem-announcing-steemstem-io) (for which a dev is looked for), and we run a [**witness**](https://steemconnect.com/sign/account_witness_vote?approve=1&witness=stem.witness) and a seed node (seed.steemstem.io:2001) to support the Steem blockchain. More information can be found on the **@steemstem** blog ([**here**](https://www.steemstem.io/#!/@steemstem/steemstem-weekly-update-week-42) for the latest news) and on our [**discord server**](https://discord.gg/Ph2beq). **We are on our way to make Steem a crucial medium for science communication, and it is still time to contribute to this effort!** If you want to support us (and get some incentives for it), this is [**also possible**](https://steemit.com/steemstem/@steemstem/get-incentives-for-promoting-stem-on-steem).