We examine the minimal supergravity (mSUGRA) model under the assumption that the strong CP problem is solved by the Peccei-Quinn mechanism. In this case, the relic dark matter (DM) abundance consists of three components: i). cold axions, ii). warm axinos from neutralino decay, and iii). cold or warm thermally produced axinos. To sustain a high enough re-heat temperature (T R > ∼ 10 6 GeV) for many baryogenesis mechanisms to function, we find that the bulk of DM should consist of cold axions, while the admixture of cold and warm axinos should be rather slight, with a very light axino of mass ∼ 100 keV. For mSUGRA with mainly axion cold DM (CDM), the most DM-preferred parameter space regions are precisely those which are least preferred in the case of neutralino DM. Thus, rather different SUSY signatures are expected at the LHC in the case of mSUGRA with mainly axion CDM, as compared to mSUGRA with neutralino CDM.
We calculate the relic abundance of thermally produced neutralino cold dark matter in the general 19 parameter supergravity (SUGRA-19) model. A scan over GUT scale parameters reveals that models with a bino-like neutralino typically give rise to a dark matter density Ωχ0 1 h 2 ∼ 1 − 1000, i.e. between 1 and 4 orders of magnitude higher than the measured value. Models with higgsino or wino cold dark matter can yield the correct relic density, but mainly for neutralino masses around 700-1300 GeV. Models with mixed bino-wino or bino-higgsino CDM, or models with dominant co-annihilation or A-resonance annihilation can yield the correct abundance, but such cases are extremely hard to generate using a general scan over GUT scale parameters; this is indicative of high fine-tuning of the relic abundance in these cases. Requiring that mχ0 1 < ∼ 500 GeV (as a rough naturalness requirement) gives rise to a minimal probably dip in parameter space at the measured CDM abundance. For comparison, we also scan over mSUGRA space with four free parameters. Finally, we investigate the Peccei-Quinn augmented MSSM with mixed axion/axino cold dark matter. In this case, the relic abundance agrees more naturally with the measured value. In light of our cumulative results, we conclude that future axion searches should probe much more broadly in axion mass, and deeper into the axion coupling.
Martin has proposed a scenario dubbed "compressed supersymmetry" (SUSY) where the MSSM is the effective field theory between energy scales M weak and M GUT , but with the GUT scale SU (3) gaugino mass M 3 ≪ M 1 or M 2 . As a result, squark and gluino masses are suppressed relative to slepton, chargino and neutralino masses, leading to a compressed sparticle mass spectrum, and where the dark matter relic density in the early universe may be dominantly governed by neutralino annihilation into tt pairs via exchange of a light top squark. We explore the dark matter and collider signals expected from compressed SUSY for two distinct model lines with differing assumptions about GUT scale gaugino mass parameters. For dark matter signals, the compressed squark spectrum leads to an enhancement in direct detection rates compared to models with unified gaugino masses. Meanwhile, neutralino halo annihilation rates to gamma rays and anti-matter are also enhanced relative to related scenarios with unified gaugino masses but, depending on the halo dark matter distribution, may yet be below the sensitivity of indirect searches underway. In the case of collider signals, we compare the rates for the potentially dominant decay modes of thet 1 which may be expected to be produced in cascade decay chains at the LHC:t 1 → c Z 1 andt 1 → bW Z 1 . We examine the extent to which multilepton signal rates are reduced when the two-body decay mode dominates. For the model lines that we examine here, the multi-lepton signals, though reduced, still remain observable at the LHC.
Over almost all of minimal supergravity (mSUGRA or CMSSM) model parameter space, there is a large overabundance of neutralino cold dark matter (CDM). We find that the allowed regions of mSUGRA parameter space which match the measured abundance of CDM in the universe are highly fine-tuned. If instead we invoke the Peccei-Quinn-Weinberg-Wilczek solution to the strong CP problem, then the SUSY CDM may consist of an axion/axino admixture with an axino mass of order the MeV scale, and where mixed axion/axino or mainly axion CDM seems preferred. In this case, fine-tuning of the relic density is typically much lower, showing that axion/axino CDM (aãCDM) is to be preferred in the paradigm model for SUSY phenomenology. For mSUGRA with aãCDM, quite different regions of parameter space are now DM-favored as compared to the case of neutralino DM. Thus, rather different SUSY signatures are expected at the LHC in the case of mSUGRA with aãCDM, as compared to mSUGRA with neutralino CDM.Keywords: Supersymmetry Phenomenology, Supersymmetric Standard Model, Dark Matter, Axions.where Ω = ρ/ρ c is the dark matter density relative to the closure density, and h is the scaled Hubble constant. No particle present in the Standard Model (SM) of particle physics has the correct properties to constitue the CDM, so some form of new physics is needed. It is compelling, however, that candidate CDM particles do emerge naturally from two theories which provide solutions to longstanding problems in particle physics.The first problem-known as the gauge hierarchy problem-arises due to quadratic divergences in the scalar sector of the SM. These divergences lead to scalar masses blowing up to the highest scale in the theory (e.g. in grand unified theories (GUTS), the GUT scale M GU T ≃ 2 × 10 16 GeV), unless an enormous fine-tuning of parameters is invoked. One solution to the gauge hierarchy problem occurs by introducing supersymmetry (SUSY) into the theory. The inclusion of softly broken SUSY leads to a cancellation of quadratic divergences between fermion and boson loops, so that only log divergences remain. The log divergence is soft enough that vastly different scales remain stable within a single effective theory. In SUSY theories, the lightest neutralino emerges as an excellent WIMP CDM candidate. Gravity-mediated SUSY breaking models (supergravity, or SUGRA) contain gravitinos with weak-scale masses. SUGRA models experience tension due to possible overproduction of gravitinos in the early universe, leading to an overabundance of CDM. In addition, gravitinos usually decay during or after Big Bang nucleosynthesis (BBN), and their energetic decay products may disrupt the successful calculations of light element abundances, which otherwise maintain good agreement with observation. This tension in SUGRA models is known as the gravitino problem.The second problem is the strong CP problem [2]. An elegant solution to the strong CP problem was proposed by Peccei and Quinn (PQ) many years ago [3]. The PQ solution automatically predicts the existence of...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.