arXiv subjects

Kari Enqvist

Publications and source records attributed to Kari Enqvist.

At least 91 records · Page 5Linked to original sources

arXiv2002

Baryogenesis in models with large extra dimensions

We describe how difficult it is to realise baryogenesis in models where the fundamental scale in nature is as low as TeV. The problem becomes even more challenging if we assume that there are only {\it two} extra compact spatial dimensions, because thermal history of such a Universe is strongly constrained by various cosmological and astrophysical bounds which translate the maximal temperature of the Universe which must not exceed $\sim {\cal O}(10)$MeV. This simply reiterates that the observed baryon asymmetry must be synthesised just above the nucleosynthesis scale. In this talk we address how to construct a simple model which can overcome this challenge.

hep-ph↗

arXiv2001

Open and closed CDM isocurvature models contrasted with the CMB data

We consider pure isocurvature cold dark matter models in the case of open and closed universe. We allow for a large spectral tilt and scan the 6-dimensional parameter space for the best fit to the COBE, Boomerang, and Maxima-1 data. Taking into account constraints from large-scale structure and big bang nucleosynthesis, we find a best fit with $χ^2 = 121$, which is to be compared to $χ^2 = 44$ of a flat adiabatic reference model. Hence the current data strongly disfavour pure isocurvature perturbations.

astro-ph↗

arXiv2001

Constraints on brane and bulk ideal fluid in Randall-Sundrum cosmologies

We investigate constraints for including bulk and brane matter in the Randall- Sundrum model. In static configurations with two zero thickness branes, we find that no realistic brane matter is possible. We also consider the possibility that the radion has stabilized by dissipating its energy into the bulk in the form of some unspecified matter, and find the Randall-Sundrum cosmological solutions in the presence of bulk ideal fluid. We discover that the metric is necessarily in a static configuration. We also discover that there is only one allowed equation of state for the bulk fluid, $p=ρ$, corresponding to the stiff ideal fluid. We find the corresponding brane cosmologies and compare them with the Friedmann-Robertson-Walker model.

hep-th↗

arXiv2001

Possible astrophysical signatures of heavy stable neutral relics in supergravity models

We consider heavy stable neutral particles in the context of supergravity and show that a gravitationally suppressed inflaton decay can produce such particles in cosmologically interesting abundances within a wide mass range $10^3 {\rm GeV} \leq m_X \leq 10^{11} {\rm GeV}$. In gravity-mediated supersymmetry breaking models, a heavy particle can decay into its superpartner and a photon-photino pair or a gravitino. Such decays only change the identity of a possible dark matter candidate. However, for $10^3 {\rm GeV} \leq m_X \leq 10^7 {\rm GeV}$, astrophysical bounds from gamma-ray background and photodissociation of light elements can be more stringent than the overclosure bound, thus ruling out the particle as a dark matter candidate.

hep-ph↗

arXiv2001

Baryogenesis in theories with large extra spatial dimensions

We describe a simple and predictive scenario for baryogenesis in theories with large extra dimensions which resembles Affleck-Dine baryogenesis. The Affleck-Dine field is a complex scalar field carrying a $U(1)_χ$ charge which is dynamically broken after the end of inflation. This generates an excess of $χ$ over $\bar χ$, which then decays into Standard Model fermions to produce an excess of baryons over anti-baryons. Our model is very constrained because the Affleck-Dine field has to be sufficiently flat during inflation. It is also a source for density fluctuations which can be tested in the coming satellite and balloon experiments.

hep-ph↗

arXiv2001

Hubble Law and Brane Matter after Ekpyrosis

We study brane matter in the ekpyrotic scenario and observe that in order to obtain standard gravity on the visible brane, the tension of the visible brane should be positive. If the sizes of both the fifth dimension and the Calabi-Yau threefold are fixed, the Israel junction conditions do not allow time-dependent brane matter. Relaxing this constraint, it is possible to obtain approximately standard cosmology on the visible brane, with small corrections due to possible time-dependence of the Calabi-Yau threefold.

hep-th↗

arXiv2001

g-2 of the muon in SUSY Models with Gauge Multiplets in the Bulk of Extra-Dimensions

We analyze the supersymmetric contributions to the anomalous magnetic moment of the muon (a_μ) in the framework of pure and gaugino-assisted anomaly mediation models, and gaugino mediation models. In the last two models the gauge multiplets propagate in the higher dimensional bulk, providing a natural mechanism for solving the problem of negative squared slepton masses present in the pure anomaly mediation models. In the light of the new BNL results for a_μ, we found that the pure and gaugino-assisted anomaly mediation models are almost excluded by the BNL constraints at 2σlevel when combined with CLEO constraints on b->sg at 90 % of C.L. In contrast, the gaugino mediation models provide extensive regions in the SUSY parameter space where both of these constraints are satisfied.

hep-ph↗

arXiv2000

Creation of large spatial fluctuations in neutrino asymmetry by neutrino oscillations

We consider active-sterile neutrino oscillations in the early universe in an inhomogeneous isocurvature background. We show that very small initial baryonic seed-inhomogeneities can trigger a growth of very large amplitude spatial fluctuations in lepton asymmetry. Domains of varying asymmetry are observed to persist for a long time despite dissipative effects. The space dependent asymmetry profiles give rise to MSW-resonances within the domain boundaries, enhancing dramatically the equilibration of the sterile neutrino species. According to our one-dimensional toy-model, the effect is so strong that almost the entire parameter space where exponential growth of asymmetry occurs would be ruled out by nucleosynthesis.

hep-ph↗

arXiv2000

Limits on isocurvature fluctuations from Boomerang and MAXIMA

We present the constraints on isocurvature fluctuations for a flat universe implied by the Boomerang and Maxima-1 data on the anisotropy of the cosmic microwave background. Because the new data defines the shape of the angular power spectrum in the region of the first acoustic peaks much more clearly than earlier data, even a tilted pure isocurvature model is now ruled out. However, a mixed model with a sizable isocurvature contribution remains allowed. We consider primordial fluctuations with different spectral indices for the adiabatic and isocurvature perturbations, and find that the 95% C.L. upper limit to the isocurvature contribution to the low multipoles is $α\leq 0.63$. The upper limit to the contribution in the $ł\sim 200$ region is $α_{200} \leq 0.13$.

astro-ph↗

arXiv2000

Recent progress in Affleck-Dine baryogenesis

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. I discuss the creation and growth of the quantum seed fluctuations which catalyse the collapse of the condensate. In D-term inflation models, the fluctuations of squark fields in the flat directions also give rise to isocurvature density fluctuations stored in the Affleck-Dine condensate. After the condensate breaks up, these can be perturbations in the baryon number, or, in the case where the present neutralino density comes directly from B-ball decay, perturbations in the number of dark matter neutralinos. The latter case results in a large enhancement of the isocurvature perturbation, which should be observable by PLANCK.

hep-ph↗

arXiv2000

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↗

arXiv1999

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↗

arXiv1999

Constraining Isocurvature Fluctuations with the Planck Surveyor

We consider the detection possibilities of isocurvature fluctuations in the future CMB satellite experiments MAP and Planck for different cosmological reference models. We present a simultaneous 10 parameter fit (8 for the case of open model) to determine the correlations between the cosmological parameters, including isocurvature cold dark matter contribution to the anisotropy. Assuming that polarization information can be fully exploited, we find that an isocurvature perturbation can be detected by the Planck Surveyor if the ratio of the initial isocurvature and adiabatic perturbation amplitude is larger than 0.07. In the absence of polarization data, the signal from isocurvature perturbations can be confused with tensor perturbations or early reionization effects, and the limit is larger by almost an order of magnitude.

astro-ph↗

arXiv1999

On chaoticity of the amplification of the neutrino asymmetry in the early universe

We consider numerically the growth of neutrino asymmetry in active-sterile neutrino oscillations in the early universe. It is shown that the final sign of the asymmetry can be highly sensitive to small variations of the oscillation parameters. We find regions which are completely or partially chaotic, but also regions where the sign remains very robust. The consequences for atmospheric neutrino oscillations and primordial nucleosynthesis are then discussed. In the completely chaotic region the predicted He(4)-abundance has an inherent arbitrariness ΔY \simeq 0.01.

hep-ph↗

arXiv1999

Testing B-ball cosmology with the CMB

In D-term inflation models, the fluctuations of squark fields in the flat directions give rise to isocurvature density fluctuations stored in the Affleck-Dine condensate. After the condensate breaks up in B-balls, these can be perturbations in the baryon number, or, in the case where the present neutralino density comes directly from B-ball decay, perturbations in the number of dark matter neutralinos. The latter case results in a large enhancement of the isocurvature perturbation. In this case, the requirement that the deviation of the adiabatic perturbations from scale invariance due to the Affleck-Dine field is not too large imposes a lower bound on the magnitude of the isocurvature fluctuation of about $10^{-2}$ times the adiabatic perturbation. This should be observable by MAP and PLANCK.

hep-ph↗

arXiv1999

Supersymmetric D-term Inflation and B-ball Baryogenesis

We consider the B-ball cosmology of the MSSM in the context of D-term inflation models where the reheating temperature is determined by the Affleck-Dine mechanism to be of the order of 1 GeV. We show that such a low reheating temperature can arise quite naturally as the result of a symmetry which is required to maintain the flatness of the inflaton potential. In this case the B-balls will decay well after the freeze-out temperature of the LSP, allowing baryons and cold dark matter to originate primarily from B-ball decays.

hep-ph↗

arXiv1998

Observable Isocurvature Fluctuations from the Affleck-Dine Condensate

In D-term inflation models, Affleck-Dine baryogenesis produces isocurvature density fluctuations. These can be perturbations in the baryon number, or, in the case where the present neutralino density comes directly from B-ball decay, perturbations in the number of dark matter neutralinos. The latter case results in a large enhancement of the isocurvature perturbation. The requirement that the deviation of the adiabatic perturbations from scale invariance due to the Affleck-Dine field is not too large then imposes a lower bound on the magnitude of the isocurvature fluctuation of about $10^{-2}$ times the adiabatic perturbation. This should be observable by MAP and PLANCK.

hep-ph↗

arXiv1998

B-ball Baryogenesis and the Baryon to Dark Matter Ratio

We demonstrate that B-ball decay in the MSSM can naturally solve the puzzle of why the densities of baryons and dark matter in the Universe are similar. This requires that the B-balls survive thermalization and decay below the freeze-out temperature of the neutralino LSP, typically 1-10GeV. It is shown that this can happen if the baryon asymmetry originates from a squark condensate along the d=6 u^{c}d^{c}d^{c} D-flat direction of the MSSM scalar potential. For this to work the reheating temperature after inflation must be no greater than 10^3-10^5 GeV.

hep-ph↗