arXiv subjects

John McDonald

Publications and source records attributed to John McDonald.

At least 73 records · Page 4Linked to original sources

arXiv2010

Cosmological evolution of scalar fields and gravitino dark matter in gauge mediation at low reheating temperatures

We consider the dynamics of the supersymmetry-breaking scalar field and the production of dark matter gravitinos via its decay in a gauge-mediated supersymmetry breaking model with metastable vacuum. We find that the scalar field amplitude and gravitino density are extremely sensitive to the parameters of the hidden sector. For the case of an O'Raifeartaigh sector, we show that the observed dark matter density can be explained by gravitinos even for low reheating temperatures T_{R} < 10 GeV. Such low reheating temperatures may be implied by detection of the NLSP at the LHC if its thermal freeze-out density is in conflict with BBN.

hep-ph↗

arXiv2009

Gauge singlet scalar as inflaton and thermal relic dark matter

We show that, by adding a gauge singlet scalar S to the standard model which is nonminimally coupled to gravity, S can act both as the inflaton and as thermal relic dark matter. We obtain the allowed region of the (m_s, m_h) parameter space which gives a spectral index in agreement with observational bounds and also produces the observed dark matter density while not violating vacuum stability or nonperturbativity constraints. We show that, in contrast to the case of Higgs inflation, once quantum corrections are included the spectral index is significantly larger than the classical value (n = 0.966 for N = 60) for all allowed values of the Higgs mass m_h. The range of Higgs mass compatible with the constraints is 145 GeV < m_h < 170 GeV. The S mass lies in the range 45 GeV < ms < 1 TeV for the case of a real S scalar with large quartic self-coupling lambdas, with a smaller upper bound for smaller lambdas. A region of the parameter space is accessible to direct searches at the LHC via h-->SS, while future direct dark matter searches should be able to significantly constrain the model.

hep-ph↗

arXiv2009

Enhanced Dark Matter Annihilation Rate for Positron and Electron Excesses from Q-ball Decay

We show that Q-ball decay in Affleck-Dine baryogenesis models can account for dark matter when the annihilation cross-section is sufficiently enhanced to explain the positron and electron excesses observed by PAMELA, ATIC and PPB-BETS. For Affleck-Dine baryogenesis along a d = 6 flat direction, the reheating temperature is approximately 30 GeV and the Q-ball decay temperature is in the range 10-100 MeV. The LSPs produced by Q-ball decay annihilate down to the observed dark matter density if the cross-section is enhanced by a factor ~ 10^3 relative to the thermal relic cross-section.

hep-ph↗

arXiv2009

keV Warm Dark Matter via the Supersymmetric Higgs Portal

Warm dark matter (WDM) may resolve the possible conflict between observed galaxy halos and the halos produced in cold dark matter (CDM) simulations. Here we present an extension of MSSM to include WDM by adding a gauge singlet fermion, \barχ, with a portal-like coupling to the MSSM Higgs doublets. This model has the property that the dark matter is {\it necessarily warm}. In the case where M_{\barχ} is mainly due to electroweak symmetry breaking, the \barχ mass is completely determined by its relic density and the reheating temperature, T_R. For 10^2 GeV < T_{R} < 10^{5} GeV$, the range allowed by \bar{chi} production via thermal Higgs annihilation, the \barχ mass is in the range 0.3-4 keV, precisely the range required for WDM. The primordial phase-space density, Q, can directly account for that observed in dwarf spheroidal galaxies, Q \approx 5 x 10^{6}(eV/cm^3)/(km/s)^3,, when the reheating temperature is in the range T_R \approx 10-100 TeV, in which case M_{\barχ} \approx 0.45 keV. The free-streaming length is in the range 0.3-4 Mpc, which can be small enough to alleviate the problems of overproduction of galaxy substructure and low angular momentum of CDM simulations.

hep-ph↗

arXiv2009

Space-Dependent Step Features: Transient Breakdown of Slow-roll, Homogeneity and Isotropy During Inflation

A step feature in the inflaton potential can model a transient breakdown of slow-roll inflation. Here we generalize the step feature to include space-dependence, allowing it also to model a breakdown of homogeneity and isotropy. The space-dependent inflaton potential generates a classical curvature perturbation mode characterized by the wavenumber of the step inhomogeneity. For inhomogeneities small compared with the horizon at the step, space-dependence has a small effect on the curvature perturbation. Therefore the smoothly oscillating quantum power spectrum predicted by the homogeneous step is robust with respect to sub-horizon space-dependence. For inhomogeneities equal to or greater than the horizon at the step, the space-dependent classical mode can dominate, producing a curvature perturbation in which modes of wavenumber determined by the step inhomogeneity are superimposed on the oscillating power spectrum. Generation of a space-dependent step feature may therefore provide a mechanism to introduce primordial anisotropy into the curvature perturbation. Space-dependence also modifies the quantum fluctuations, in particular via resonance-like features coming from mode coupling to amplified superhorizon modes. However these effects are small relative to the classical modes.

astro-ph↗

arXiv2009

Cosmological Constraints on Unparticles as Continuous Mass Scalars

We study the cosmological constraints on unparticle interactions and the temperature of the Universe for the case where unparticle states can be modelled as continuous mass particles with lifetime > 1s. By considering thermal background quark decay to continuous mass scalars via a scalar operator of dimension d_{U}, we show that the condition that the Universe is not dominated by scalars at nucleosynthesis imposes a lower bound on the scale of the interaction of the unparticle sector, with M_{U} > 20-2600 TeV for Λ_{U} > 1 \TeV$, 1.1 < d_{U} < 2.0 and 2 < d_{BZ} < 4. The existence of a long-lived scalar sector also imposes an upper bound on the temperature of the Universe during radiation-domination, which can be as low as a TeV for M_{U} close to its lower bound.

hep-ph↗

arXiv2008

Supersymmetric inflation and baryogenesis via Extra-Flat directions of the MSSM

One interpretation of proton stability is the existence of extra-flat directions of the MSSM, in particular $u^{c}u^{c}d^{c}e^{c}$ and $QQQL$, where the operators lifting the potential are suppressed by a mass scale $Λ$ which is much larger than the Planck mass, $ Λ\gae 10^{26} \GeV$. Using D-term hybrid inflation as an example, we show that such flat directions can serve as the inflaton in SUSY inflation models. The resulting model is a minimal version of D-term inflation which requires the smallest number of additional fields. In the case where $Q$-balls form from the extra-flat direction condensate after inflation, successful Affleck-Dine baryogenesis is possible if the suppression mass scale is $\gae 10^{31}-10^{35} \GeV$. In this case the reheating temperature from $Q$-ball decay is in the range $3-100 \GeV$, while observable baryon isocurvature perturbations and non-thermal dark matter are possible. In the case of extra-flat directions with a large $t$ squark component, there no $Q$-ball formation and reheating is via conventional condensate decay. In this case the reheating temperature is in the range $1-100 \TeV$, naturally evading thermal gravitino overproduction while allowing sphaleron erasure of any large B-L asymmetry.

hep-ph↗

arXiv2008

Unparticles: Interpretation and Cosmology

We discuss the physical interpretation of unparticles and review the constraints from cosmology. Unparticles may be understood in terms of confined states of a strongly-coupled scale-invariant theory, where scale-invariance implies that the confined states have continuous masses. This picture is consistent with the observation that unparticle operators can be represented in terms of continuous mass fields. Finite results in scattering processes are obtained by compensating the infinite number of unparticle final states with an infinitesimal coupling per unparticle. As a result, unparticles are stable with respect to decay or annihilation to Standard Model particles, implying a one-way flow of energy from the Standard Model sector to the unparticle sector. The qualitative properties of unparticles, which result from their continuous mass nature, are unchanged in the case where scale-invariance is broken by a mass gap. Unparticles with a mass gap can evade constraints from astrophysical and 5th force considerations, in which case cosmology provides the strongest constraints.

hep-ph↗

arXiv2008

Z_2-Singlino Dark Matter in a Portal-Like Extension of the Minimal Supersymmetric Standard Model

We propose a Z_2-stabilised singlino (\barχ) as a dark matter candidate in extended and R-parity violating versions of the supersymmetric standard model. \barχ interacts with visible matter via a heavy messenger field S, which results in a supersymmetric version of the Higgs portal interaction. The relic abundance of \barχ can account for cold dark matter if the messenger mass satisfies M_S \lsim 10^{4} GeV. Our model can be implemented in many realistic supersymmetric models such as the NMSSM and nMSSM.

hep-ph↗

arXiv2008

Supergravity and Two-Field Inflation Effects in Right-Handed Sneutrino-Modified D-term Inflation

We extend previous work on the minimal D-term inflation model modified by Right-Handed (RH) sneutrino fields to include additional inflaton-sector SUGRA corrections and two-field inflation effects. We show that SUGRA corrections simultaneously allow n_{s} to be within 3-year WMAP limits and the cosmic string contribution to the CMB power spectrum to be less than 5%. For gauge coupling g < 1, the CMB contribution from cosmic strings is predicted to be at least 1% while the spectral index is predicted to be less than 0.968 for a CMB string contribution less than 5%. Treating the inflaton-RH sneutrino system as a two-field inflation model, we show that the time-dependence of the RH sneutrino field strongly modifies the single-field results for values of RH sneutrino mass m_Φ > 0.1 H. The running spectral index is α= -0.0002 when m_Φ < 0.1 H but increases to positive values as m_Φ/H increases, with α> 0.008 for m_Φ > 1.0 H.

hep-ph↗

arXiv2008

Type-II Seesaw at Collider, Lepton Asymmetry and Singlet Scalar Dark Matter

We propose an extension of the standard model with a B-L global symmetry that is broken softly at the TeV scale. The neutrinos acquire masses through a type-II seesaw while the lepton (L) asymmetry arises in the {\it singlet sector} but without B-L violation. The model has the virtue that the scale of L-number violation ($Λ$) giving rise to neutrino masses is independent of the scale of leptogenesis ($Λ'$). As a result the model can explain {\it neutrino masses, singlet scalar dark matter and leptogenesis at the TeV scale}. The stability of the dark matter is ensured by a surviving $Z_2$ symmetry, which could be lifted at the Planck scale and thereby allowing Planck scale-suppressed decay of singlet scalar dark matter particles of mass $\approx 3$ MeV to $e^+ e^-$ pairs in the Galactic halo. The model also predicts a few hundred GeV doubly charged scalar and a long lived charged fermion, whose decay can be studied at Large Hadron Collider (LHC) and International Linear Collider (ILC).

hep-ph↗

arXiv2007

RH Sneutrino Condensate CDM and the Baryon-to-Dark Matter Ratio

The similarity of the observed mass densities of baryons and cold dark matter may be a sign they have a related origin. The baryon-to-dark matter ratio can be understood in the MSSM with right-handed (RH) neutrinos if CDM is due to a d = 4 flat direction condensate of very weakly coupled RH sneutrino LSPs and the baryon asymmetry is generated by Affleck-Dine leptogenesis along a d = 4 (H_{u}L)^2 flat direction. Observable signatures of the model include CDM and baryon isocurvature perturbations and distinctive long-lived NLSP phenomenology.

hep-ph↗

arXiv2007

Gauge Singlet Scalars as Cold Dark Matter

In light of recent interest in minimal extensions of the Standard Model and gauge singlet scalar cold dark matter, we provide an arXiv preprint of the paper, published as Phys.Rev. D50 (1994) 3637, which presented the first detailed analysis of gauge singlet scalar cold dark matter.

hep-ph↗

arXiv2006

Right-Handed Sneutrino Condensate Cold Dark Matter and the Baryon-to-Dark Matter Ratio

The similarity of the observed densities of baryons and cold dark matter suggests that they have a common or related origin. This can be understood in the context of the MSSM with right-handed (RH) sneutrinos if cold dark matter is due to a d = 4 flat direction condensate of very weakly coupled RH sneutrino LSPs and the baryon asymmetry is generated by Affleck-Dine leptogenesis along the d = 4 (H_{u}L)^{2} flat direction. The correct density of RH sneutrino dark matter is obtained if the reheating temperature is in the range 10^{6}-10^{8} GeV. A cold dark matter isocurvature perturbation close to present observational bounds is likely in the case of inflation driven by a D-term or by an F-term with suppressed Hubble corrections to the A-terms. An observable baryon isocurvature perturbation is also possible in the case of D-term inflation models.

hep-ph↗

arXiv2006

Supergravity Modification of D-term Hybrid Inflation: Solving the Cosmic String and Spectral Index Problems via a Right-Handed Sneutrino

Supergravity corrections due to the energy density of a right-handed sneutrino can generate a negative mass squared for the inflaton, flattening the inflaton potential and reducing the spectral index and inflaton energy density. For the case of D-term hybrid inflation, we show that the spectral index can be lowered from the conventional value n = 0.98 to a value within the range allowed by the latest WMAP analysis, n = 0.951^{+0.015}_{-0.019}. The modified energy density is consistent with non-observation of cosmic strings in the CMB if n < 0.946. The WMAP lower bound on the spectral index implies that the D-term cosmic string contribution may be very close present CMB limits, contributing at least 5% to the CMB multipoles.

hep-ph↗

arXiv2006

F-Term Inflation Q-Balls

A general analysis of Q-ball solutions of the supersymmetric F-term hybrid inflation field equations is given. The solutions consist of a complex inflaton field and a real symmetry breaking field, with a conserved global charge associated with the inflaton. It is shown that the Q-ball solutions for any value of the superpotential coupling, κ, may be obtained from those with κ= 1 by rescaling the space coordinates. The complete range of Q-ball solutions for the case κ= 1 is given, from which all possible F-term inflation Q-balls can be obtained. The possible role of F-term inflation Q-balls in cosmology is discussed.

hep-th↗

arXiv2005

Simulations of the End of Supersymmetric Hybrid Inflation and Non-Topological Soliton Formation

We present two- and three-dimensional simulations of the growth of quantum fluctuations of the scalar fields in supersymmetric hybrid inflation models. For a natural range of couplings, sub-horizon quantum fluctuations undergo rapid growth due to scalar field dynamics, resulting in the formation of quasi-stable non-topological solitons (inflaton condensate lumps) which dominate the post-inflation era.

hep-ph↗

arXiv2004

Conditions for a Successful Right-Handed Majorana Sneutrino Curvaton

We consider the conditions which must be satisfied for a Majorana RH sneutrino, a massive right-handed (RH) sneutrino associated with the see-saw mechanism of Majorana neutrino masses, to play the role of the curvaton. Planck-scale suppressed non-renormalizable terms in the RH neutrino superpotential must be eliminated to a high order if the RH sneutrino curvaton is to dominate the energy density before it decays, which can be achieved via an R-symmetry which is broken to R-parity by the Giudice-Maseiro mechanism. In order to satisfy the thermalization constraint, one RH neutrino mass eigenstate must have small Yukawa couplings to the Higgs and lepton doublets, corresponding to a lightest neutrino mass m_{nu_{1}} < 10^{-3} eV. A time-dependent lepton asymmetry will be induced in the RH sneutrino condensate by the Affleck-Dine mechanism driven by SUSY breaking B-terms associated with the RH neutrino masses. Requiring that the resulting baryon asymmetry and isocurvature perturbations are acceptably small imposes an upper bound on the RH neutrino mass. We show that a scenario consistent with all constraints is obtained for a RH neutrino mass in the range 10^{2} - 10^{4} GeV when the RH sneutrino decay temperature is greater than 100 GeV and lightest neutrino mass m_{nu_{1}} approx 10^{-3} GeV. Larger RH neutrino masses are possible for smaller m_{nu_{1}}. The resulting scenario is generally consistent with a solution of the cosmic string problem of D-term inflation.

hep-ph↗