Exploring Ultralight Scalar Assistance inSterile Neutrino Dark Matter:
Cold Spectrum and Unusual X/Gamma-ray Signatures
Yuxuan He（何雨轩）Peking University
2023.12.5@KASHIWA DARK MATTERSYMPOSIUM 2023
JCAP 09 (2023) 047 2305.08095,
YXH , Jia Liu, Xiaolin Ma and Xiao-Ping Wang

Introduction• Sterile neutrino dark matter• Dodelson-Widrow (DW) mechanism• Mixing induced Gamma/X ray signals

S. Dodelson and L. M. Widrow 1994

K. Abazajian et. al. 1705.01837

Introduction• WDM constraints
Sterile neutrino produced in DW mechanism have thermal
distribution, there are stringent constraints on light DM. DW
I. Zelko et. al 2205.09777
sterile neutrino DM mass need
• Alternative production mechanisms of sterile neutrino dark
matter
Shi-Fuller mechanism
X. Shi and G. M. Fuller. 9810076
A. Kusenko et. al. 1006.1731
GUT-scale scenario
Higgs production mechanism K. Petraki and A. Kusenko, 0711.4646
A. Berlin and D. Hooper, 1610.03849
Ultralight Scalar assistant production

Ultralight Scalar Assistance production mechanism• Basic idea
Consider a time dependent mixing angle
time dependent

Induced by couple to ultralight back ground scalar fieldmixing angle takes large value at early universe
Sin θ
But tiny at today
time dependent
φ field

Ultralight Scalar Assistance production mechansim• Model set up
Begin with following LagrangianAfter diagonalization
We get field dependent mixing angle

Ultralight scalar obeying EOM

Ultralight Scalar Assistance production mechanism• Production driven by ultralight scalar

Ultralight Scalar Assistance production mechanism• Constraints on parameter space• Long range force between DM mediated byultralight scalar
H. Davoudiasl et. al, 1804.01098
S. C. F. Morris et. al., 1304.2196• mixing term induced dark matter decay• We choose parameter space

Cold Spectrum• Energy spectrum of DW sterile neutrino
The effective mixing angle isNeglect tiny terms
withsterile neutrino takes thermal distribution

Cold Spectrum• Colder spectrum due to time dependent mixing angle
When production during oscillation
approximately
the distribution given bySpectrum suppressed in large y• Colder spectrum due to entropy injection

Cold Spectrum• Even more cool spectrum
scalar coupling changed tothen
Previous argument give
AndSterile neutrino DM can befurther cold

Cold Spectrum• Transfer function and constraints
Can be fit with thWDM
P. Bode, J. P. Ostriker, and N. Turok. 2001

uThe DW mechanism
mass should larger
92keVLess constrainedUnusual X/Gamma-ray Signatures• Today‘s scalar field takes tiny value• The local scalar field is also relied on density dependent
potential
Which have stationary field value

And scalar field oscillate around its stationary value

Unusual X/Gamma-ray Signatures• Density dependence of scalar field• The scalar field will saturated atmaximalwithUnusual X/Gamma-ray Signatures• Density dependent mixing angle• Unusual density dependent flux

Unusual X/Gamma-ray Signatures• Constraints from X/Gamma-ray observations

Conclusion• Scalar assistant mechanism for sterile neutrino DM
production can relax X/Gamma ray constraints• This mechanism can successfully provide a colder dark
matter spectrum compared with DW mechanism• With sterile neutrino scalar coupling, there are detectable
X/Gamma ray signals with density dependent feature.

Thank You

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• Boltzmann eq

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• Effects that cool the spectrum• Transfer function of thWDM

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