Research
Stellar evolution with physics beyond the Standard Model
Stellar evolution and structure arise from various particle and nuclear processes, so stars can be used as a laboratory of fundamental physics.
Intermediate-mass stars with ~10Msun deviate from the red giant branch and form a loop in the Hertzsprung-Russell diagram during central He burning.
This blue loop is sensitive to input physics and thus can be used as a probe of exotic physics. In our study, we focus on the neutrino magnetic moment (NMM). They enhance the energy loss rates to change the stellar evolutionary path. We find that
the blue loop is eliminated when the effect of the NMM is too large. Stars in the blue loops are
observed as classical Cepheid variables and blue giants in reality, so the elimination can be used to constrain the NMM.
We conclude that the upper limit of the NMM is 2×10-10µB, where µB is the Bohr magneton.
The additional energy loss also affects the structure of low-mass stars. We find that, when the NMM is ~5×10-12µB,
the surface lithium abundance in red clump stars can be enhanced because of more efficient internal mixing. On the other hand, recent spectropic observations
of red clump stars revealed that the estimated lithium abundance is significantly higher than the standard stellar models.
Our results imply that exotic energy losses may mitigate the discrepancy between the observations and theoretical models.
References:
K. Mori, T. J. Moriya, T. Takiwaki, K. Kotake, S. Horiuchi and S. I. Blinnikov, 2023, The Astrophysical Journal, 943, 12.
K. Mori, T. Takiwaki and K. Kotate, 2022, Physical Review D, 105, 023020.
K. Mori, M. Kusakabe, A. B. Balantekin, T. Kajino and M. A. Famiano, 2021, Monthly Notices of the Royal Astronomical Society, 503, 2746. (Codes and inlists are available)
K. Mori, A. B. Balantekin, T. Kajino and M. A. Famiano, 2020, The Astrophysical Journal, 898, 163.
K. Mori and K. Nomoto, 2020, Symmetry, 12, 404.
Type Ia supernova
Type Ia supernovae (SNe Ia) are thought
to be a thermonuclear explosion of a white dwarf (WD). It is famous
that they are used as a standard candle in cosmology. In addition to
that, they produce a large amount of Fe group elements and play an
important role in the galactic chemical evolution. However, their
progenitor is not well understood. In one scenario called
single-degenerate, it is attributed to accretion on a WD whose mass is
approaching the Chandrasekhar limit. In the other scenario called
double-degenerate, it is thought to be a WD-WD binary merger. I aim to
reveal the nature of the progenitor and SN Ia explosion itself from the
point of view of nucleosynthesis.
Ignition of SNe Ia is caused by the
12C+12C reaction,
although its low-energy cross sections are not known. If there are
resonances in the low-energy region, the reaction rates will be
enhanced. I investigated the effects of such resonances on WD-WD
mergers, and found that they tend to collapse into a neutron star due
to the enhanced reaction rates.
References:
K. Mori, 2021, Publications of the Astronomical Society of Japan, 73, 1382.
K. Mori, T. Suzuki, M. Honma, M. A. Famiano, T, Kajino, M. Kusakabe and A. B. Balantekin, 2020, The Astrophysical Journal, 904, 29.
K. Mori, M. A. Famiano, T. Kajino, M. Kusakabe and X. Tang, 2019,
Monthly Notices of the Royal Astronomical Society, 482, L70.
K. Mori, M. A. Famiano, T. Kajino, T. Suzuki, P. Garnavich, G. J.
Mathews, R. Diehl, S. -C. Leung and K. Nomoto, 2018, The Astrophysical
Journal, 863, 176.
K. Mori, M. A. Famiano, T. Kajino, T. Suzuki, J. Hidaka, M. Honma, K.
Iwamoto, K. Nomoto and T. Otsuka, 2016, The Astrophysical Journal, 833,
179.
Core-collapse supernova
Massive stars end their life as core-collapse supernovae. The extreme environment in supernovae offers an oppotunity to probe physics beyond the Standard Model.
In particular, heavy axion-like particles (ALPs) that couple with photons may be produced in the supernova core and work as an additional heating source. We implemented ALPs in a supernova simulation code and discussed their effect on supernova dynamics.
We find that ALPs with the mass of ~100 MeV can heat the stalled shock and lead to successful explosion even in one-dimansional models. The explosion energy reaches ~1052 erg in some models, which exceeds the typical values for observed events.
References:
K. Mori, T. Takiwaki, K. Kotake and S. Horiuchi, 2022, Physical Review D, 105, 063009.
Big Bang nucleosynthesis
In Big Bang nucleosynthesis (BBN), light
elements including H, He and Li are produced.
Predictions from BBN theories and astronomical observations of
primordial abundances are consistent excluding 7Li, so it is thought
that BBN is "well-understood". Therefore, it is possible to use BBN as
a probe of beyond-standard physics in the early Universe. I studied the
effect of quark mass variations on BBN, and confined them by comparing the theoretical prediction with
precise measurements of primordial D abundances. In addition,
it was found that there is a parameter region in which the
primordial Li abundance is reduced significantly.
References:
K. Mori and M. Kusakabe, 2019, Physical Review D, 99, 083013.