The dark universe: the interplay of cosmological moduli, axions, and the MSSM

In this work, we introduce two effective field theories which parameterize a light modulus field interacting both with the MSSM ($\phi$MSSM) and with the MSSM combined with an additional supersymmetric DFSZ axion ($\phi$PQMSSM). All two-body decays of the modulus are cataloged and connected to explicit string scenarios, with all model-independent decay widths calculated incorporating mixing and phase-space effects for the first time. Dark matter and dark radiation production are studied in both models for a subset of string scenarios, with comments provided on expectations for the remaining scenarios. Quite generally, we find that many string scenarios with a modulus-driven early matter dominated period overproduce dark matter and/or dark radiation. The overproduction of dark matter may be remedied with a sufficiently large modulus mass, however various consistency conditions show that most scenarios are incompatible with weak-scale supersymmetry and with a DFSZ-type axion, at least without additional model-building. We also study statistical properties of the Peccei-Quinn scale $f_a$ and the derived value of the SUSY $\mu$-term in the string landscape. Here, we find the predicted value of $f_a$ is in the cosmological sweet-spot for axion dark matter, while the predicted higgsino masses are slightly above current LHC bounds. Additionally, we study the predicted nature of viable dark matter candidates in explicit inflationary scenarios in string theory, finding a WIMP in K\"{a}hler inflation and open string axions in fibre inflation to be natural dark matter candidates

The Dark Universe after Reheating in String Inflation

We study the production of dark matter and dark radiation after reheating in string inflation models where the Calabi-Yau has a fibred structure and the visible sector lives on D3 branes. We show how the interplay between different physical constraints from inflation, reheating, supersymmetry breaking and dark radiation, leads to distinct predictions for the nature of dark matter.Comment: 12 pages, 4 figure

Is the magnitude of the Peccei-Quinn scale set by the landscape?

Rather general considerations of the string theory landscape imply a mild statistical draw towards large soft SUSY breaking terms tempered by the requirement of proper electroweak symmetry breaking where SUSY contributions to the weak scale are not too far from m(weak)~ 100 GeV. Such a picture leads to the prediction that m_h~ 125 GeV while most sparticles are beyond current LHC reach. Here we explore the possibility that the magnitude of the Peccei-Quinn (PQ) scale f_a is also set by string landscape considerations within the framework of a compelling SUSY axion model. First, we examine the case where the PQ symmetry arises as an accidental approximate global symmetry from a more fundamental gravity-safe Z(24)^R symmetry and where the SUSY mu parameter arises from a Kim-Nilles operator. The pull towards large soft terms then also pulls the PQ scale as large as possible. Unless this is tempered by rather severe (unknown) cosmological or anthropic bounds on the density of dark matter, then we would expect a far greater abundance of dark matter than is observed. This conclusion cannot be negated by adopting a tiny axion misalignment angle theta_i because WIMPs are also overproduced at large f_a. Hence, we conclude that setting the PQ scale via anthropics is highly unlikely. Instead, requiring soft SUSY breaking terms of order the gravity-mediation scale m_{3/2}~ 10-100 TeV places the mixed axion-neutralino dark matter abundance into the intermediate scale sweet zone where f_a~ 10^{11}-10^{12} GeV. We compare our analysis to the more general case of a generic SUSY DFSZ axion model with uniform selection on theta_i but leading to the measured dark matter abundance: this approach leads to a preference for f_a~ 10^{12} GeV.Comment: 24 pages plus 10 figure

The dark universe after reheating in string inflation

Abstract We study the production of dark matter and dark radiation after reheating in string inflation models where the Calabi-Yau has a fibred structure and the visible sector lives on D3 branes. We show how the interplay between different physical constraints from inflation, reheating, supersymmetry breaking and dark radiation, leads to distinct predictions for the nature of dark matter. In particular, in Fibre Inflation dark matter can only be primordial black holes or an open string QCD axion with an intermediate scale decay constant since WIMPs are always too heavy and ultralight closed string axions cannot behave as fuzzy dark matter due to strong isocurvature bounds. On the other hand, Kähler moduli inflation can allow for non-thermal WIMP dark matter at the TeV-scale

Dark matter and dark radiation from the early universe with a modulus coupled to the PQMSSM

Abstract The supersymmetrized DFSZ axion model is especially compelling in that it contains 1. the SUSY solution to the gauge hierarchy problem, 2. the Peccei-Quinn (PQ) solution to the strong CP problem and 3. the Kim-Nilles solution to the SUSY μ problem. In a string setting, where a discrete R-symmetry ( Z 24 R $${\textbf{Z}}_{24}^R$$ for example) may emerge from the compactification process, a high-quality accidental axion (accion) can emerge from the accidental, approximate remnant global U(1)PQ symmetry where the decay constant f a is linked to the SUSY breaking scale, and is within the cosmological sweet zone. In this setup, one also expects the presence of stringy remnant moduli fields ϕ i . Here, we consider the situation of a single light modulus ϕ coupled to the PQMSSM in the early universe, with mixed axion plus higgsino-like WIMP dark matter. We evaluate dark matter and dark radiation production via nine coupled Boltzmann equations and assess the severity of the cosmological moduli problem (CMP) along with dark matter and dark radiation production rates. We find that typically the light modulus mass should be m ϕ ≳ 104 TeV to avoid the moduli-induced dark matter overproduction problem. If one is able to (anthropically) tune the modulus field amplitude, we find a value of ϕ 0 ≲ 10–7 m P would be required to solve the overall CMP