Searcharxiv⌕ Search

arXiv subjects

John McDonald

Publications and source records attributed to John McDonald.

At least 91 records · Page 5Linked to original sources

Flat Direction Dynamics in a Non-Topological Soliton-Dominated Universe

In hybrid inflation and running mass inflation models it is possible that the inflaton field will fragment into non-topological solitons, resulting in a highly inhomogeneous post-inflation era prior to reheating. In supersymmetric models with a conventional homogeneous post-inflation era, the dynamics of flat direction scalars are determined by cH^{2} corrections to the mass squared terms, coming from the energy density of the Universe combined with Planck-scale suppressed interactions. Here we reconsider the cH^{2} corrections for a Universe dominated by inflatonic non-topological solitons. We show that the dynamics in this case are typically equivalent to the case c = 0, even in the vicinity of the non-topological solitons. Thus Affleck-Dine baryogenesis will proceed as in the original c = 0 Affleck-Dine scenario.

hep-ph↗

Curvaton Potential Terms, Scale-Dependent Perturbation Spectra and Chaotic Initial Conditions

The curvaton scenario predicts an almost scale-invariant spectrum of perturbations in most inflation models. We consider the possibility that renormalisable phi^4 or Planck scale-suppressed non-renormalisable curvaton potential terms may result in an observable deviation from scale-invariance. We show that if the curvaton initially has a large amplitude and if the total number of e-foldings of inflation is less than about 300 then a running blue perturbation spectrum with an observable deviation from scale-invariance is likely. D-term inflation is considered as an example with a potentially low total number of e-foldings of inflation. A secondary role for the curvaton, in which it drives a period of chaotic inflation leading to D-term or other flat potential inflation from an initially chaotic state, is suggested.

hep-ph↗

Two-Field Q-ball Solutions of Supersymmetric Hybrid Inflation

We demonstrate the existence of two-field Q-ball solutions of the scalar field equations of supersymmetric D- and F-term hybrid inflation. The solutions consist of a complex inflaton field together with a real symmetry breaking field. Such inflatonic Q-balls may play a fundamental role in reheating and the post-inflation era of supersymmetric hybrid inflation models.

hep-ph↗

Supersymmetric Curvatons and Phase-Induced Curvaton Fluctuations

We consider the curvaton scenario in the context of supersymmetry (SUSY) with gravity-mediated SUSY breaking. In the case of a large initial curvaton amplitude during inflation and a negative order H^2 correction to the mass squared term after inflation, the curvaton will be close to the minimum of its potential at the end of inflation. In this case the curvaton amplitude fluctuations will be damped due to oscillations around the effective minimum of the curvaton potential, requiring a large expansion rate during inflation in order to account for the observed energy density perturbations, in conflict with cosmic microwave background constraints. Here we introduce a new curvaton scenario, the phase-induced curvaton scenario, in which de Sitter fluctuations of the phase of a complex SUSY curvaton field induce an amplitude fluctuation which is unsuppressed even in the presence of a negative order H^2 correction and large initial curvaton amplitude. This scenario is closely related to the Affleck-Dine mechanism and a curvaton asymmetry is naturally generated in conjunction with the energy density perturbations. Cosmological energy density perturbations can be explained with an expansion rate H ~ 10^12 GeV during inflation.

hep-ph↗

F-Term Hybrid Inflation, the η-problem and Extra Dimensions

F-term hybrid inflation models in the context of supergravity generically have corrections to the inflaton mass squared of the order of H^{2} (the η-problem). In addition they have a problem with large deviations of the spectrum of density perturbations from scale-invariance due to non-renormalizable corrections to the superpotential. Here we show that an increase of the expansion rate at large energy densities relative to that in conventional d=4 cosmology, as suggested by the single brane Randall-Sundrum scenario with an uncompactified extra dimension, can naturally solve the ηproblem. This requires that the d=5 Planck mass satisfies M_{5} < 10^{16} GeV. In addition, the scale-invariance of the density perturbation spectrum can be generally protected from Planck-suppressed superpotential corrections if M_{5} < 10^{10} \GeV

hep-ph↗

Right-Handed Sneutrinos as Curvatons

We consider the possibility that a right-handed sneutrino can serve as the source of energy density perturbations leading to structure formation in cosmology. The cosmological evolution of a coherently oscillating condensate of right-handed sneutrinos is studied for the case where reheating after inflation is due to perturbative inflaton decays. For the case of Dirac neutrinos, it is shown that some suppression of Planck scale-suppressed corrections to the right-handed neutrino superpotential is necessary. cH^2 corrections to the sneutrino mass squared term must also be suppressed during inflation (|c| < 0.1), in which case, depending on the magnitude of |c| during inflation, a significantly blue (if c > 0) or red (if c < 0) perturbation spectrum is possible. R-parity must also be broken in order to ensure that the Universe is not overclosed by LSPs from the late decay (at temperatures 1-10 MeV) of the right-handed sneutrino condensate. The resulting expansion rate during inflation can be significantly smaller than in conventional supersymmetric inflation models (as low as 10^6 GeV is possible). For the case of Majorana neutrinos, a more severe suppression of Planck-suppressed superpotential corrections is required. In addition, the Majorana sneutrino condensate is likely to be thermalised before it can dominate the energy density, which would exclude the Majorana right-handed sneutrino as a curvaton.

hep-ph↗

Growth of Inflaton Perturbations and the Post-Inflation Era in Supersymmetric Hybrid Inflation Models

It has been shown that hybrid inflation may end with the formation of non-topological solitons of inflaton field. As a first step towards a fully realistic picture of the post-inflation era and reheating in supersymmetric hybrid inflation models, we study the classical scalar field equations of a supersymmetric hybrid inflation model using a semi-analytical ansatz for the spatial dependence of the fields. Using the minimal D-term inflation model as an example, the inflaton field is evolved using the full 1-loop effective potential from the slow-rolling era to the U(1)_{FI} symmetry-breaking phase transition. Spatial perturbations of the inflaton corresponding to quantum fluctuations are introduced for the case where there is spatially coherent U(1)_{FI} symmetry breaking. The maximal growth of the dominant perturbation is found to depend only on the ratio of superpotential coupling λto the gauge coupling g. The inflaton condensate fragments to non-topological solitons for λ/g > 0.09. Possible consequences of non-topological soliton formation in fully realistic SUSY hybrid inflation models are discussed.

hep-ph↗

Inflaton Condensate Fragmentation in Hybrid Inflation Models

Inflation ends with the formation of a Bose condensate of inflatons. We show that in hybrid inflation models this condensate is typically unstable with respect to spatial perturbations and can fragment to condensate lumps. The case of D-term inflation is considered as an example and it is shown that fragmentation occurs if λ> 0.2g, where λis the superpotential coupling and g is the U(1)_{FI} gauge coupling. Condensate fragmentation can result in an effective enhancement of inflaton annihilations over decays as the main mode of reheating. In the case of D-term inflation models in which the Standard Model fields carry U(1)_{FI} charges, if condensate fragmentation occurs then reheating is dominated by inflaton annihilations, typically resulting in the overproduction of thermal gravitinos. Fragmentation may also have important consequences for SUSY flat direction dynamics and for preheating.

hep-ph↗

Thermally Generated Gauge Singlet Scalars as Self-Interacting Dark Matter

We show that a gauge singlet scalar S, with a coupling to the Higgs doublet of the form lambda_{S} S^{\dagger}S H^{\dagger}H and with the S mass entirely generated by the Higgs expectation value, has a thermally generated relic density Omega_{S} \approx 0.3 if m_{S} \approx (2.9-10.5)(Omega_{S}/0.3)^{1/5}(h/0.7)^{2/5} MeV for Higgs boson masses in the range 115 GeV to 1 TeV. Remarkably, this is very similar to the range (m_{S} = (6.6-15.4)η^{2/3} MeV) required in order for the self-interaction (η/4)(S^{\dagger}S)^{2} to account for self-interacting dark matter when ηis not much smaller than 1. The corresponding coupling is lambda_{S} \approx (2.7 \times 10^{-10} - 3.6 \times 10^{-9})(Omega_{S}/0.3)^{2/5}(h/0.7)^{4/5}, implying that such scalars are very weakly coupled to the Standard Model sector.

hep-ph↗

Non-Thermal Dark Matter, High Energy Cosmic Rays and Late-Decaying Particles From Inflationary Quantum Fluctuations

It has been suggested that the origin of cosmic rays above the GZK limit might be explained by the decay of particles, X, with mass of the order of 10^{12} GeV. Generation of heavy particles from inflationary quantum fluctuations is a prime candidate for the origin of the decaying X particles. It has also been suggested that the problem of non-singular galactic halos might be explained if dark matter originates non-thermally from the decay of particles, Y, such that there is a free-streaming length of the order of 0.1Mpc. Here we explore the possibility that quantum fluctuations might account for the Y particles as well as the X particles. For the case of non-thermal WIMP dark matter with unsuppressed weak interactions we find that there is a general problem with deuterium photo-dissociation, disfavouring WIMP dark matter candidates. For the case of more general dark matter particles, which may have little or no interaction with conventional matter, we discuss the conditions under which X and Y scalars or fermions can account for non-thermal dark matter and cosmic rays. For the case where X and Y scalars are simultaneously produced, we show that galactic halos are likely to have a dynamically significant component of X scalar cold dark matter in addition to the dominant non-thermal dark matter component.

hep-ph↗

Q-ball Evolution, B-ball Baryogenesis and the f_{B} Problem

We consider some of the issues surrounding the formation and evolution of Q-balls in the MSSM and its extensions. The ratio of the baryon number packed into Q-balls to that outside, f_{B}, plays a fundamental role in determining the relationship of dark matter to the baryon number in the Universe at present. The final value of f_{B} will depend upon the details of the formation of Q-balls from the collapse of the Affleck-Dine condensate and upon the subsequent evolution of the ensemble of Q-balls. We discuss the implications for neutralino dark matter in the gravity-mediated scenario and show that a light neutralino is necessary in most cases to account for the baryon to dark matter ratio, with an NMSSM singlino LSP of mass m_χ \lae 20 \GeV being a favoured candidate.

hep-ph↗

Dynamical Cosmological Constant from A Very Recent Phase Transition

Observation indicates that the expansion of the Universe is accelerating and favours a dynamical cosmological constant, Λ(t). We consider the possibility that this is due to a scalar field which has undergone a very recent phase transition. We study a simple class of model, corresponding to a ϕ^4 potential with a time-dependent mass squared term. For the models considered the phase transition occurs at a red shift z \leq 1.2. The evolution of the equation of state ω_ϕ and energy density ρ_ϕ with time is distinct from existing dynamical Λmodels based on slowly rolling fields, with ω_ϕ and ρ_ϕ rapidly changing in a characteristic way following the transition. The ϕenergy density is composed of a time-dependent vacuum energy and coherently oscillating condensate component with a negative pressure. The condensate component will collapse to form non-topological soliton lumps, 'ϕ-axitons', which smoothly populate the Universe.

hep-ph↗

Naturally Large Cosmological Neutrino Asymmetries in the MSSM

A large neutrino asymmetry is an interesting possibility for cosmology, which can have significant observable consequences for nucleosynthesis and the cosmic microwave background. However, although it is a possibility, there is no obvious reason to expect the neutrino asymmetry to be observably large. Here we note that if the baryon asymmetry originates via the Affleck-Dine mechanism along a d=4 flat direction of the MSSM scalar potential and if the lepton asymmetry originates via Affleck-Dine leptogenesis along a d=6 direction, corresponding to the lowest dimension directions conserving R-parity, then the ratio n_{L}/n_{B} is naturally in the range 10^{8}-10^{9}. As a result, a potentially observable neutrino asymmetry is correlated with a baryon asymmetry of the order of 10^{-10}.

hep-ph↗

Inflationary Affleck-Dine Scalar Dynamics and Isocurvature Perturbations

We consider the evolution of the Affleck-Dine scalar during D-term and F-term inflation and solve the combined slow-roll equations of motion. We show that for a typical case, where both the Affleck-Dine scalar and inflaton initially have large values, in D-term inflation the Affleck-Dine scalar is driven to a fixed value, with only a very slight dependence on the number of e-foldings. As a result, there is a definite prediction for the ratio of the baryonic isocurvature perturbation to the adiabatic perturbation. In minimal (d=4) Affleck-Dine baryogenesis the relative isocurvature contribution to the CMB angular power spectrum amplitude is predicted to be in the range $0.01-0.1$, which can account for present large-scale structure observations and should be observable by PLANCK. In a very general case, scale-invariance of the adiabatic perturbations from the Affleck-Dine scalar imposes a lower bound of about 0.01 for d=4. For d=6 the isocurvature perturbation may just be observable, although this is less certain. We also consider F-term inflation and show that the magnitude of the baryonic isocurvature perturbation is fixed by the value of $H$ during inflation. For typical values of $H$ the isocurvature perturbation could be close to present observational limits.

hep-ph↗

Reheating Temperature and Inflaton Mass Bounds from Thermalization After Inflation

We consider the conditions for the decay products of perturbative inflaton decay to thermalize. The importance of considering the full spectrum of inflaton decay products in the thermalization process is emphasized. It is shown that the delay between the end of inflaton decay and thermalization allows the thermal gravitino upper bound on the reheating temperature to be raised from 10^{8} GeV to as much as 10^{12} GeV in realistic inflation models. Requiring that thermalization occurs before nucleosynthesis imposes an upper bound on the inflaton mass as a function of the reheating temperature, m_{S} < 10^{10} (T_{R}/1 GeV)^{7/9} GeV. It is also shown that even in realistic inflation models with relatively large reheating temperatures, it is non-trivial to have thermalization before the electroweak phase transition temperature. Therefore the thermal history of the Universe is very sensitive to details of the inflation model.

hep-ph↗

Symmetry Non-Restoration via Order 10^{-10} B and L Asymmetries

It has been observed that a large lepton asymmetry, n_{L}/s \approx 0.1, can prevent the Higgs expectation value from going to zero at high temperature, resulting in the non-restoration of the SU(2)XU(1) gauge symmetry and other symmetries. This could allow for the elimination of domain walls and other dangerous topological defects. Here we show that if the reheating temperature after inflation, T_{R}, is sufficiently low then symmetry non-restoration will occur with an asymmetry of the order of the observed baryon asymmetry, n_{B}/s \approx 10^{-10}. For this to occur T_{R} \leq 1 GeV is necessary. Remarkably, this happens to be the reheating temperature expected in Affleck-Dine baryogenesis along a d=6 flat direction of the MSSM. As an example, we show that this can neatly solve the Z_{3} domain wall problem of the NMSSM.

hep-ph↗

The Dynamics of Affleck-Dine Condensate Collapse

In the MSSM, cosmological scalar field condensates formed along flat directions of the scalar potential (Affleck-Dine condensates) are typically unstable with respect to formation of Q-balls, a type of non-topological soliton. We consider the dynamical evolution of the Affleck-Dine condensate in the MSSM. We discuss the creation and linear growth, in F- and D-term inflation models, of the quantum seed perturbations which in the non-linear regime catalyse the collapse of the condensate to non-topological soliton lumps. We study numerically the evolution of the collapsing condensate lumps and show that the solitons initially formed are not in general Q-balls, but Q-axitons, a pseudo-breather which can have very different properties from Q-balls of the same charge. We calculate the energy and charge radiated from a spherically symmetric condensate lump as it evolves into a Q-axiton. We also discuss the implications for baryogenesis and dark matter.

hep-ph↗