WHAT I THINK ABOUT WHEN I THINK ABOUT DARK MATTER

Transcription

1 WHAT I THINK ABOUT WHEN I THINK ABOUT DARK MATTER MASS 2015, Odense, May 2015 Ray Volkas School of Physics The University of Melbourne

2 Apologies to Raymond Carver and Haruki Murakami J

3 Part 1: An approach to the dark matter mass scale in asymmetric dark matter models. Part 2: A new DM direct detection experiment in the southern hemisphere.

4 Part 1: The dark matter mass scale in asymmetric dark matter models.

5 I will follow a line of thinking about the nature of dark matter that makes sense to me: asymmetric dark matter (ADM) Take home points: Ø Visible and dark mass density coincidence Ø Visible mass density from baryogen. and QCD Ø ADM connects VM and DM number densities Ø Seemingly no choice: DM is a dark baryon of a dark QCD to get DM mass density correct Ø Grand unified visible & dark sectors

6 What do we know about DM? DM ' 5 VM It looks cold, but may be a little bit warm or just chilled. Galactic and sub-galactic anomalies exist (core vs cusp, satellites, too big to fail ). Effectively collisionless on extra-galactic scales (but very recent claim of DM self-int. at cluster scales). Forms spheroidal haloes.

7 What DM is not: hot relic, e.g. ordinary neutrinos. What DM does not do: Ø Accumulate in neutron stars, form BHs and eat the stars. Ø Drastically affect stellar evolution. Ø Get produced at 7&8 TeV pp collisions. Ø Etc. How DM teases us: DAMA, CoGeNT, SuperCDMS, LUX, etc. 130 GeV line, 3.5 kev line, PAMELA, Hooperon. Probably will think of new and unusual ways in the future. J

8 Let me obsess about: DM ' 5 VM m D n D ' 5 m V n V proton mass Λ QCD Baryon-antibaryon asymmetry n B n B n s

9 m D n D ' 5 m V n V Obvious hint: n D n V m D m V = m p ' GeV The WIMP miracle, by contrast, has (usually) m D m V = m p ' GeV n D n V The miracle is that this works for non-rel, thermal freeze-out with weak-scale DM annihilation cross-section.

10 One person s miracle may be another s coincidence! Anybody s BSM theory. Includes WIMP theories. Includes my theories. Includes your theories. Theory built on the foundations of reality. Unique example: Standard Model.

11 Look at n D n V first. Only sensible choice: asymmetric DM. Dark baryons, dark antibaryons. Dark baryo genesis. Review: K.Petraki and RV, IJMP A28 (2013) ; Conserved baryon-number-like quantum number during chemical equilibrium between visible and dark sectors => the related number densities. Allows, not mandates, DM to be: multi-component, self-interacting, come with dark radiation,

12 Case 1: Baryon-symmetric universe Dodelson and Widrow: PRL 64 (1990) 340 Davoudiasl et al: PRL 105 (2010) Bell, Petraki, Shoemaker, RV: PRD 84 (2011) Conserved: B con (B L) V B D Cheung, Zurek: PRD 84 (2011) von Harling, Petraki, RV: JCAP 1205 (2012) 021 others see for full reference list. Broken: B bro (B L) V + B D At early times and high temperatures: B bro violated but B con strictly conserved. At late times and low temperatures, B V and B D are separately conserved ensures stability of protons and DM. Generate B bro asymmetry using dynamics obeying Sakharov conditions. Then ((B L) V )= (B D )= (B bro )/2 where =(n n)/s The B-L number of VM is secretly cancelled by the DM!

13 Simultaneous creation of correlated asymmetries. Pangenesis Cogenesis ((B L) V )= (B bro )/2 Stabilising (B D )= (Bconserved bro )/2 (baryon) number VISIBLE SECTOR DARK SECTOR

14 Case 2: visible to dark reprocessing Initially, (B-L) V is broken but B D is not. asymmetry created here During the chemical equilibration, some non-trivial combination of (B-L) V and B D is conserved. The sectors subsequently decouple. ((B L) V ) 6= 0 VISIBLE SECTOR shared s.t. ((B L) V ) (B D ) (B D ) 6= 0 DARK SECTOR

15 Case 3: dark to visible reprocessing Initially, B D is broken but (B-L) V is not. During the chemical equilibration, some non-trivial combination of (B-L) V and B D is conserved. asymmetry created here The sectors subsequently decouple. ((B L) V ) 6= 0 VISIBLE SECTOR shared s.t. ((B L) V ) (B D ) (B D ) 6= 0 DARK SECTOR

16 Asymmetry generation Creating an asymmetry (Sakharov 1967): 1. Violation of particle number conservation 2. C and CP violation 3. Out-of-equilibrium process 1. Obvious Rate i! f( B = b) 6= Rate ī! f( B = b) Rate i! f( B = b) 6= Rate f! i( B = b)

17 Common general mechanisms: Out-of-equilibrium decays of heavy particles: (! x 1 x 2...) 6= (! x 1 x 2...) Affleck-Dine: production of charged scalar condensate through time-dep. phase. Supersymmetry, uses flat directions. First-order phase transition: nucleation of bubbles of true vacuum, sphalerons, CP-violating collisions with bubble walls. Out-of-equilibrium scattering: DM particles scatter/coannihilate with SM particles at a different rate from DM antiparticles. NEW! Baldes, Bell, Petraki, RV: PRL 113 (2014) 18, and Baldes, Bell, Millar, Petraki, RV: JCAP 1411 (2014) 11, 041 Asymmetric thermal production (asymmetric freeze-in): DM and anti-dm never in thermal equilibrium; slowly produced at different rates. Spontaneous genesis: Sakharov conditions presuppose CPT invariance. Expanding universe induces effective CPT violation. Asymmetry generation in eq. without C, CP violation.

18 There are many models, many variations, many possible phenomenological and observational consequences; won t review them here. Instead I want to focus on the second issue: the origin of (dark matter) mass. This is a neglected topic in the ADM literature. For ADM to be really compelling, we need a theory for both DM number density (easy) and DM mass (harder). Origin of mass? No, not the Higgs

19 Origin of visible (i.e. nucleon) mass is QCD. The up and down quark masses, from the Higgs, are a few MeV; nothing to do with proton mass. The strong coupling constant becomes large at about 200 MeV: the QCD confinement scale, Λ QCD. If the DM mass scale is really similar to the proton mass, then the reason may be a dark QCD. Image credit: Siegfried Bethke

20 Why might there be a dark QCD with a similar confinement scale to visible QCD? Maybe dark matter is grand unified with ordinary matter.

21 An obvious starting point is the mirror matter model : [ SU(3) SU(2) U(1) ] V [ SU(3) SU(2) U(1) ] D Vß à D discrete symmetry Foot; RV; Berezhiani, Bento, Comelli, Mohapatra, Villante; H.-J. He et al If the discrete sym. is unbroken: SU(3) V and SU(3) D running couplings exactly the same, so m D = m V = m p (mirror nuclei). Need n D 5n V. Symmetric microphysics, asymmetric macrophysics.

22 Follow similar starting point but different development here. G V x G D with Vß à D and G V =G D =SU(5), SO(10), Grand-unified hidden-sector dark matter G V breaks to the SM. S.J. Lonsdale and RRV, arxiv: , PRD D90 (2014) S.J. Lonsdale, arxiv: Have G D break differently, but contain an unbroken SU(3) D. Asymmetric symmetry breaking

23 One example: SU(5) V x SU(5) D <24> 0 <10> 0 SU(3) D xsu(2) D SU(3) V xsu(2) V xu(1) V Doublet from 5* SU(3) V xu(1) Q m q,v m q,d Different quark and dark quark mass thresholds => different running Doublet from 45 SU(3) D

24 Asymmetric symmetry breaking 1 $ 2, 1 $ 2 1=visible, 2=dark V = ( v 2 ) 2 + ( v 2 ) 2 +,, apple, apple,, > 0 +apple apple ( v 2 v 2 ) 2 Φ sector nonzero χ sector nonzero either Φ 1 or Φ 2 zero either χ 1 or χ 2 zero If Φ 1 0 then χ 1 =0 etc. h 1 i = v, h 2 i =0 h 1 i =0, h 2 i = v

25 L H GeVL Non-susy Need at least one very light dark quark to form the DM baryon. 5 massive 1 light 100 target area massive 5 light m H GeVL dark quark mass Greater # of massive dark quarks => faster running of dark QCD coupling => higher dark confinement scale

26 For SU(5) x SU(5), the slightly different running for QCD and dark QCD must be due to different quark and dark quark mass thresholds. For SO(10) x SO(10), it can also be due to different symmetry breaking cascades in the two sectors. For example: SO(10) V à SU(5) V à SU(3) V SO(10) D à SO(8) D à SU(3) V

27 40 Α 1 35 U SU 2 SU 5 20 SU 3 SO 8 15 SU 3 GeV Susy case

28 Susy case M GeV Log 10 M I GeV D V SU(3) V and SU(4) D above intermediate scale M I

29 No complete model yet constructed: Ø Asymmetry generation mechanism Ø Chemical reprocessing b/w VM and DM Ø Annihilate symmetric part of dark plasma Ø Solve all GUT pheno problems Ø Understand dark hadron sector Simple alternative, giving up on grand unification: Just SMß à SM with asymmetric sym. breaking. Ø Different quark/dark quark mass thresholds. Ø Don t have hierarchy problem, no susy needed. Ø No ad hoc elements needed as gauge coupling constant unification not required. (S. Lonsdale, RV, under development. This is a variation on other broken mirror models considered by various authors see earlier list.)

30 Summary of Part 1: DM and VM may be closely related and have a common micro- and macrophysical origin: asymmetric DM, interesting phenomenology possible. Need a theory of why DM mass ~ few GeV. If DM is part of a hidden gauge theory, what becomes of grand unification? One possibility is GxG with asymmetric symmetry breaking: dark QCD à DM mass. Successful parameter space does exist. Of course, life is simpler without grand unification or susy: broken mirror model using asymmetric symmetry breaking, with full dynamics, being constructed.

31 Part 2: A new dark matter direct detection experiment in the southern hemisphere. The following slides are courtesy of my colleague Elisabetta Barberio, who is leading the project.

32 Basic idea: Test dark matter interpretation of DAMA/Libra annual modulation signal by having identical high radio purity NaI crystal detectors in Gran Sasso and Stawell Gold Mine, Australia. Summer/winter systematic effects OPPOSITE in phase in the two hemispheres. Dark matter effects have SAME phase.

33 SABRE: Sodium iodide with Ac2ve Background REjec2on Dual- linked experiment: one part in Gran Sasso (Italy) and one in Stawell (Australia) Developing and tes2ng low background NaI(Tl) scin2lla2ng crystals that exceed the radio- purity of DAMA/LIBRA (driven by F. Calaprice - Princeton). > NO ONE SUCCEEDED TO DO THIS. A well- shielded ac2ve veto to reduce internal and external background New low background and high QE PMTs and low radioac2vity copper housing U, Th < μbq/kg Current SABRE Collabora9on Princeton University (Led by Frank Calaprice) main driver; University of Houston, PNNL, Gran Sasso Na2onal Lab, Milano University; Roma la Sapienza University, University of Melbourne, Australian Na2onal University.

34 DAMA/LIBRA Energy spectrum DAMA/LIBRA signal region: 2-6 kev. Background from 40 K decay? 13 ppb K in DAMA crystals. Single hit spectrum Eur. Phs. C (2008)

35 ACTIVE VETO Goal: lower background, lower threshold, and higher sensi2vity than DAMA. DAMA/LIBRA signal region: 2-6 kev. Background from 40 K decay? 13 ppb K in DAMA crystals. Ultra-high purity NaI(Tl) detector + Active veto detector

36 Tes2ng Dama 25 Kg of these new crystals+ac2ve veto can test DAMA/Libra in 3 years

37 Possible configura2on of Sabre veto with Shielding Cylinder: 1.5 m x 1.5 m ~2 tons LAB scin2llator inch PMTs Reflector in inner surface Expected: 0.22 p.e./kev Shielding: 20-25cm steel Water filled chamber.

38 Australian Site Stawell gold mine ~240 km west of Melbourne, will host the first ready to be used underground laboratory in the Southern hemisphere. Stawell Underground Physics Laboratory (SUPL)

39 Australian Site Near the Grampians Na2onal Park

40 Stawell Gold Mine Decline gold mine mine, 1.6 km deep, with many caverns. All sites served with electricity, op2cal fibre, reached by car/truck.

41 Stawell Gold Mine The background radiation measurements are performed in 2 different locations that can be ventilated, at 730 m, 880 m and 1.02 km

42 Stawell Mine 1km We chose a site at 1.02km underground, ~3 km water equivalent (similar to Gran Sasso).

43 Stawell Mine 1km A new tunnel will be excavated

44 Underground lab A delega2on of Italian scien2sts, including Antonio Masiero (INFN Vice President) & Stefano Ragazzi (LNGS Director) visited the site. The new lab will also house scien2fic experiments from different fields e.g. astrophysics, biology, geosciences and engineering. It will be very similar to Boulby or Canfranc in size. The design is ongoing with the help of Gran Sasso and Boulby. Funding of AUD 3.5m from the Sate Government of Victoria and the Australian Federal Government has been secured. Cavern excava2on and clean room construc2on will start later this year, to be completed end Addi2onal funding is being sought.

45 Underground labs with Crystals DAMA Sabre KIMS Sabre DM Ice

46 Stawell Time line Sabre Lab proposed Funding secured (Jan) Extra funding (May) Start construc2on (Aug) Facility ready (Nov- Dec) Detector goes in NaI(Tl) crystal growth study (small crystal) Proof of concept (Gran Sasso) First Large crystal growth Large crystal detector tested/ operated in DS veto SABRE veto vessel (Melbourne) Large Array (>50kg) of NaI(Tl) detectors in opera2on

47 Outlook Hunting for Dark Matter is difficult. Direct detection experiment are challenging and many results are contradictory, depending on the technology. The DAMA/LIBRA modulation is still a mystery. A new dual North-South Hemisphere crystal experiment may settle the issue. End of 2016 the first underground physics lab in the Southern Hemisphere will be operational. After that