Cosmology
Our group mainly works in the interphase between particle physics and cosmology. Our research topics include the dark matter and dark energy problems and baryogenesis problem, cosmic inflation and inhomogeneous cosmologies. Group currently consists of two permanent staff members, one postdoctoral researcher and five PhD-students.
Contact person: Kimmo Kainulainen
- Group members
Senior researchers- Kimmo Kainulainen, professor
- Sami Nurmi, university lecturer
- Mindaugas Karciauskas, postdoctoral researcher
- Pyry M. Rahkila, doctoral student
- Henri Jukkala, doctoral student
- Olli Koskivaara, doctoral student
- Laura Laulumaa, doctoral student
- Juuso Leskinen, doctoral student
- Niyati Venkatesan
- Recent research
Our recent work includes studies of electroweak baryogenesis and dark matter in models featuring extended scalar sectors to the SM providing portal to dark sector. We also worked out novel isocurvature constraints on very weakly coupled portal dark matter models, impelled by inflation.
- Dark Matter »
The work on DM model building has to be supplemented by a careful evaluation of constraints coming from particle physics experiments as well as from cosmological observations. This way one may hope to identify models that are both theoretically appealing and observationally viable. One theoretical motivation for extending the Standard Model of particle physics, apart from getting DM, is to obtain the coupling constant unification. We have shown this to be possible in the particular minimal walking technicolor context (Figures at right), in a model that also provides a natural DM candidate. Models with extended scalar sectors became very popular after the discovery of the Higgs boson. We have participated in this research from beginning [15,3,5,8,9,11]. Recently we have shown that inflation places interesting, rather generic lower limits on the coupling between the dark and the standard model sectors in models which are essentially completely decoupled from the SM sector [5].
- Dark Energy »
We have studied alternative solutions for the DE problem from the above mentioned aspects. On one hand we have considered Scalar-Tensor-modifications of GR motivated by large extra dimensions. We have also carefully analyzed the solar system constraints on the so called f(R)-gravity models. On the other hand, we are interested in cosmological models with large scale inhomogeneities as well as in modelling propagation of light through a stochastic distribution of different scale inhomogeneities.
- Baryogenesis and quantum transport theory »
Equally puzzling as are the dark matter and dark energy problems, is the question of the origin of the matter in the Universe; why is there only matter and not at all antimatter? In our group we study the properties of the finite-temperature electroweak phase transition in extensions of the Standard Model (SM) and test these models for a succesfull baryogenesis in the electroweak scale. We also study different realizations of leptogenesis mechanism for the same effect. This work is accompanied by a strong effort to develop quantum transport equations, that can accurately describe the complicated out-of-equilibrium physics involving C- and CP-violation and quantum (de)coherences. - Inflation »
Inflation is deeply rooted in the standard model of cosmology, the main reason being its succesful prediction of the primordial density fluctuation spectrum. Our group has a long record of research on this front. Recently we have studied the evolution of the Higgs and other scalar fields both during inflation and reheating accounting for their non-minimal couplings to space-time curvature. We derive novel constraints on the SM and its extensions from vacuum stability [14] and from limits to isocurvature perturbations, which may originate from primordial condensates of scalars different from the inflaton field [5, 23]. In particular we constrain scalar DM models with weakly coupled hidden sectors in this way, systematically accounting for the initial conditions set by inflation [1]. Our research on gravitational particle production at reheating revealed novel opportunities to use the isocurvature DM bounds in constraining the mass scales and curvature couplings of weakly coupled spectator scalars [4]. Other active topics of our research include inflationary generation of magnetic fields and direct observational imprints of spectator scalars, or moduli fields.
- Model building: simple UV-complete models? »
Just as DM the BG-problem poses clear challenge to model building. The observed value of Higgs boson suggests that SM may be an UV complete theory on its own right. However, the DM and BG-problems still remain unsolved. It is therefore of interest to try to find low energy extension of SM that would be UV-complete and explain the origin of DM and the matter antimatter asymmetry. We have studied these problems in the context of singlet (S), two-Higgs doublet (2HD) and combined 2HD+S-extensions of the SM (see in particular [11] and [15]). It turns out to be very difficult to explain both the DM and baryon asymmetry in any simple model. Yet, a possible, and intriguing way out might be that baryogenesis was seeded by a CP-violation in the Dark sector.
- Dark Matter »
- Recent publications »
[1] Sami Nurmi, Tommi Tenkanen and Kimmo Tuominen,Inflationary Imprints on Dark Matter, JCAP 1511 (2015) 11, 001, arXiv:1506.04048.
[2] Kari Enqvist, Sami Nurmi, Stanislav Rusak and David Weir, Lattice Calculation of the Decay of Primordial Higgs Condensate, JCAP 1602 (2016) no.02, 057, arXiv:1506.06895 [astro-ph.CO].
[3] Kimmo Kainulainen, Kimmo Tuominen, Ville Vaskonen, Self-interacting dark matter and cosmology of a light scalar mediator, Phys.Rev. D93 (2016) no.1, 015016, arXiv:1507.04931.
[4] Tommi Markkanen and Sami Nurmi, Isocurvature constraints on gravitational particle production at reheating, arXiv:1512.07288.
[5] Kimmo Kainulainen, Sami Nurmi, Tommi Tenkanen, Kimmo Tuominen and Ville Vaskonen, Isocurvature Constraints on Portal Couplings, JCAP 1606 (2016) no.06, 022, arXiv:1601.07733.
[6] Vera-Maria Enckell, Kari Enqvist and Sami Nurmi, Observational signatures of Higgs inflation, JCAP 1607 (2016) no.07, 047, arXiv:1603.07572.
[7] Mindaugas Karčiauskas, Dynamical Analysis of Anisotropic Inflation, Mod.Phys.Lett. A31 (2016) no.21, 1640002 arXiv:1604.00269.
[8] Matti Heikinheimo, Tommi Tenkanen, Kimmo Tuominen and Ville Vaskonen, Observational Constraints on Decoupled Hidden Sectors, Phys.Rev. D94 (2016) no.6, 063506, arXiv:1604.02401.
[9] Tommi Tenkanen and Ville Vaskonen, Reheating the Standard Model from a hidden sector, Phys.Rev. D94 (2016) no.8, 083516, arXiv:1606.00192.
[10] Tommi Tenkanen, Kimmo Tuominen and Ville Vaskonen, A Strong Electroweak Phase Transition from the Inflaton Field, JCAP 1609 (2016) no.09, 037, arXiv:1606.06063.
[11] Tommi Alanne, Kimmo Kainulainen, Kimmo Tuominen and Ville Vaskonen, Baryogenesis in the two doublet and inert singlet extension of the Standard Model, JCAP 1608 (2016) no.08, 057, arXiv:1607.03303.
[12] Kari Enqvist, Mindaugas Karciauskas, Oleg Lebedev, Stanislav Rusak and Marco Zatta, Postinflationary vacuum instability and Higgs-inflaton couplings, JCAP 1611 (2016) 025, arXiv:1608.08848.
[13] Matti Herranen, Andreas Hohenegger, Asgeir Osland and Anders Tranberg, Quantum corrections to inflation: the importance of RG-running and choosing the optimal RG-scale, Phys. Rev. D95 (2017) no.2, 023525 (2017), arXiv:1608.08906.
- Other selected publications »
[14] Matti Herranen, Tommi Markkanen, Sami Nurmi and Arttu Rajantie, Spacetime curvature and Higgs stability after inflation, Phys.Rev.Lett. 115 (2015) 241301, arXiv:1506.04065.
[15] James M. Cline, Kimmo Kainulainen, Pat Scott and Christoph Weniger, Update on scalar singlet dark matter, Phys.Rev. D88 (2013) 055025, Phys.Rev. D92 (2015) 3, 039906.
[16] Christian Fidler, Matti Herranen, Kimmo Kainulainen and Pyry M. Rahkila, Flavoured quantum Boltzmann equations from cQPA, JHEP 1202 (2012) 065.
[17] Kimmo Kainulainen and Valerio Marra, Accurate Modeling of Weak Lensing with the sGL Method, Phys. Rev. D83 (2011) 023009.
[18] Matti Herranen, Kimmo Kainulainen and Pyry M. Rahkila, Towards a kinetic theory for fermions with quantum coherence, Nucl. Phys. B810 (2009), 389-426.
[19] Kimmo Kainulainen, Johanna Piilonen, Vappu Reijonen and Daniel Sunhede, Spherically symmetric spacetimes in F(R) gravity theories, Phys. Rev. D76:024020 (2007).
[20] Kimmo Kainulainen and Daniel Sunhede, Dark energy, scalar tensor gravity and large extra dimensions, Phys. Rev. D73:083510 (2006).
[21] James M. Cline, Michael Joyce and Kimmo Kainulainen, Supersymmetric Electroweak Baryogenesis, JHEP 0007:018:2000, Erratum ibid [hep-ph/0110031].
[22] Michael Joyce, Kimmo Kainulainen and Tomislav Prokopec, First principle derivation of semiclassical force for electroweak baryogenesis, JHEP 0106:031 (2001).
[23] Kari Enqvist, Tuukka Meriniemi and Sami Nurmi, Generation of the Higgs Condensate and Its Decay after Inflation, JCAP 1310 (2013) 057.