BEYOND THE STANDARD MODEL

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Physics beyond the Standard Model (BSM) refers to the theoretical developments needed to explain the deficiencies of the Standard Model, such as the inability to explain the fundamental parameters of the standard model, the strong CP problem, neutrino oscillations, matter–antimatter asymmetry, and the nature of dark matter and dark energy.[1] Another problem lies within the mathematical framework of the Standard Model itself: the Standard Model is inconsistent with that of general relativity, and one or both theories break down under certain conditions, such as spacetime singularities like the Big Bang and black hole event horizons.

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Theories that lie beyond the Standard Model include various extensions of the standard model through supersymmetry, such as the Minimal Supersymmetric Standard Model (MSSM) and Next-to-Minimal Supersymmetric Standard Model (NMSSM), and entirely novel explanations, such as string theory, M-theory, and extra dimensions. As these theories tend to reproduce the entirety of current phenomena, the question of which theory is the right one, or at least the "best step" towards a Theory of Everything, can only be settled via experiments, and is one of the most active areas of research in both theoretical and experimental physics [1]

 

Gravity

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​The standard model does not explain gravity. The approach of simply adding a graviton to the Standard Model does not recreate what is observed experimentally without other modifications, as yet undiscovered, to the Standard Model. Moreover, the Standard Model is widely considered to be incompatible with the most successful theory of gravity to date, general relativity. [2]

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For the moment, the best option is to include the graviton as a Hypothetical Tensor Boson element.

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Dark Matter​

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The nature of dark matter (DM) is currently one of the most intriguing questions of fundamental physics. Even if the question of dark matter finds its roots in astrophysics and cosmology, it is also actively searched for in particle physics experiments, at colliders as well as in dark matter detection experiments, which aim at discovering dark matter particles.

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The main experimental challenge comes of course from the elusive nature of dark matter. In addition to dark matter, several other cosmological questions remain unanswered, such as the nature of dark energy, the properties of the inflationary period, the existence of phase transitions in the early Universe, and the origin of baryon asymmetry in the Universe. In the context of particle physics, dark matter can be made of one or several new particles, which are expected to be electrically neutral, uncoloured, weakly-interacting and stable. Since the Standard Model (SM) fails at providing a dark matter candidate, it is necessary to consider scenarios beyond the Standard Model, which may in addition have a broad phenomenology at colliders.

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New physics scenarios generally rely on new symmetries which are broken at high energies or extra-dimensions, and as such they can impact the properties of the early Universe, either by the presence of new particles in the primordial thermal bath, or via phase transitions. ​

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Dark Energy

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Cosmological observations tell us the standard model explains about 5% of the energy present in the universe. About 26% should be dark matter, which would behave just like other matter, but which only interacts weakly (if at all) with the Standard Model fields. Yet, the Standard Model does not supply any fundamental particles that are good dark matter candidates. [3]

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Neutrino masses​

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According to the standard model, neutrinos are massless particles. However, neutrino oscillation experiments have shown that neutrinos do have mass. Mass terms for the neutrinos can be added to the standard model by hand, but these lead to new theoretical problems. For example, the mass terms need to be extraordinarily small and it is not clear if the neutrino masses would arise in the same way that the masses of other fundamental particles do in the Standard Model. [5]

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Matter–antimatter asymmetry​

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The universe is made out of mostly matter. However, the standard model predicts that matter and antimatter should have been created in (almost) equal amounts if the initial conditions of the universe did not involve disproportionate matter relative to antimatter. Yet, there is no mechanism in the Standard Model to sufficiently explain this asymmetry.  [5]

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