New Cosmological Data Presents 𝜈 Opportunities

Joel Meyers

SMU

Mitchell Conference

5-23-2024

Image Credits: PICO; ATLAS; Hahn, Abel; Caltech-JPL

History of the Universe

2

Image Credit: NASA

Cosmological Measurement of Neutrino Mass

• DESI BAO, combined with CMB data, now allows for tightest yet constraint on sum of neutrino masses

​

​

​

​

• Uncertainty is approaching level necessary for detection of minimum mass implied by flavor oscillations

3

DESI (2024)

​

​

Negative Neutrino Mass?

• Measurements actually favor negative neutrino mass

​

​

​

​

• This measurement disfavors the minimal mass for the normal hierarchy (58 meV) at 99% confidence

​

4

Craig, Green, JM, Rajendran (2024)

​

​

Cosmic Neutrino Background

5

Cosmic Neutrino Background

6

Image Credit: Symmetry Magazine

Cosmic neutrinos are light thermal relics from the early universe

C𝜈B makes up significant fraction of radiation energy density at early times

Massive neutrinos act like hot dark matter affecting structure growth at more recent times

Cosmic Neutrino Background -

Instantaneous Decoupling Model

7

Cosmic neutrinos decoupled from the thermal plasma around 1 MeV, and were then diluted relative to photons by electron-positron annihilation

Cosmic neutrino background makes up a significant fraction of the energy density prior to recombination

Image Credit: Baumann

Cosmic Neutrino Background -

Precision Model

The energy density of the cosmic neutrino background can be calculated precisely, including the effects of non-instantaneous weak decoupling

8

Neutrino Differential Visibility

Escudero Abenza (2020); Akita, Yamaguchi (2020); Froustey, Pitrou, Volpe (2020);

Bennett, et al (2021); Bond, Fuller, Grohs, JM, Wilson (2024)

Massive Cosmic Neutrinos

Cosmic neutrino background provides an abundance of non-relativistic neutrinos

​

​

Cosmology is sensitive to the gravitational effects of the cosmic neutrino background, allowing a measurement of a sum of neutrino masses

​

9

Super-Kamiokande (1999); Sudbury Neutrino Observatory (2001); CMB-S4 (2016)

​

​

Massive Neutrinos Suppress Matter Clustering

The large velocities of cosmic neutrinos causes them to free stream out of potential wells and suppress the growth of structure on scales smaller than their free-streaming length

10

Suppression of matter clustering due to massive neutrinos

(A_s, Ω_mh², Ω_bh², H₀ fixed)

Hu, Eisenstein, Tegmark (1998); Cooray (1999); Abazajian, et al (2011);

Green, JM (2021); Gerbino, Grohs, Lattanzi, et al (2022)

​

​

Cosmological Probes of Neutrino Mass

11

Value of Cosmological Neutrino Mass Measurement

Particle Physics

• Absolute neutrino mass scale sets a target for complementary lab-based searches for neutrino mass

Astrophysics

• Multiple probes of matter power allow neutrino mass to be disentangled from nonlinear and baryonic effects

Cosmology

• Provides end-to-end test of cosmic history and is sensitive to new massive species (including gravitinos)

12

Cosmology Excluded

0𝜈𝛽𝛽 Excluded

Inverted

Normal

Green, JM (2021); Gerbino, Grohs, Lattanzi, et al (2022)

​

​

Measuring Clustering with Cosmological Surveys

• Galaxy number density, galaxy weak lensing, counts of galaxy clusters, and weak lensing of the cosmic microwave background (among other probes) are sensitive to the clustering of matter across a wide range of scales and redshifts
• CMB lensing provides an unbiased measurement of integrated matter clustering in the linear regime

13

Green, JM (2021)

​

​

Sensitivity regimes of various probes of clustering

Unlensed CMB Polarization

14

Unlensed E

Unlensed B

𝝓

Image Credit: Guzman

​

​

5°✕5° simulated maps

Lensed CMB Polarization

15

Lensed E

Lensed B

𝝓

Image Credit: Guzman

​

​

5°✕5° simulated maps

CMB Lensing Reconstruction

16

Planck (2018)

​

​

40𝜎 observation

Neutrino Mass with CMB Lensing

17

Measuring suppression of clustering with CMB-S4 lensing

Planck (2018); CMB-S4 (2016); Green, JM (2021)

​

​

CMB Measurements of the Primordial Amplitude

• Measurements of the CMB power spectra at ℓ>30 tightly constrain the combination A_se^-2𝜏, while polarization at ℓ<20 is sensitive to 𝜏²
• Large scale polarization is most easily measured with a CMB satellite or balloon-borne CMB experiment

18

Planck (2018); Figure Credit: Reichardt (2015)

​

​

Planck 2018:

Matter Density with Baryon Acoustic Oscillations

• Spectroscopic galaxy surveys such as DESI precisely measure the expansion history using Baryon Acoustic Oscillations (BAO) as a standard ruler
• This provides a precise determination of the matter density, essential for a calibration of the amplitude of the matter power spectrum

19

DESI (2024)

​

​

Current Measurement

• Planck + ACT Lensing + DESI BAO measurements favor negative neutrino mass

​

​

​

​

• This measurement disfavors the minimal mass for the normal hierarchy (58 meV) at 99% confidence

​

20

Craig, Green, JM, Rajendran (2024)

​

​

Possible Explanations

21

Optical Depth Systematic

• The best-fit value of the optical depth has evolved over time
• A shift much larger than the statistical error on 𝜏 would be required to explain inference of negative neutrino mass

22

Craig, Green, JM, Rajendran (2024)

​

​

Matter Density Systematic

• The preference for negative neutrino mass could be explained by a shift to the matter density
• Measurements of matter density have remained roughly consistent over time

23

Craig, Green, JM, Rajendran (2024)

​

​

New Physics?

24

Massive neutrinos do not cluster like cold dark matter

Dark matter clustering is suppressed in presence of free-streaming neutrinos

Craig, Green, JM, Rajendran (2024)

​

​

Neutrinos become non-relativistic at high redshift

New Physics for Vanishing Neutrino Mass

• Neutrino decay

​

• Neutrino annihilation

​

• Neutrino cooling or heating

​

• Time-varying mass

25

Craig, Green, JM, Rajendran (2024)

​

​

New Physics for Negative “Neutrino Mass”

• New long-range force for dark matter

​

​

• Primordial trispectrum that mimics CMB lensing

26

Enhancement from long-range force on dark matter

Craig, Green, JM, Rajendran (2024)

​

​

Conclusion

27

Conclusion

28

Image Credits: Planck; BEBC/CERN; Springel, et al; Alvarez, Kaehler, Abel

Particle Physics

Cosmology

Astrophysics

New Insights

29

Thank You!

Backup Slides

30

Improved Lensing Measurement with Small Correlated Against Large Estimator (SCALE)

31

CMB-S4

Simons Observatory

Chan, Hlozek, JM, van Engelen (2023)

​

​

BBN and New Physics in the Neutrino Sector

​

​

The precision with which we can measure primordial light element abundances (especially deuterium and Helium-4) allows us to use BBN as a powerful probe of new physics

​

This becomes an even sharper test when combined with CMB constraints

32

Fischler, JM (2010); Lague, JM (2020);

Bond, Fuller, Grohs, JM, Wilson (2024);

Yeh, Shelton, Fields, Olive (2022)