Small scale structure and composite dark sectors. Sean Tulin

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1 Small scale structure and composite dark sectors Sean Tulin

2 Outline Motivation Astrophysics (small scale structure) ST & Haibo Yu (Physics Reports, to appear soon) Minimal dark baryons: SU(2) + one flavor Anthony Francis, R. Jamie Hudspith, Randy Lewis, ST (work in progress)

3 Motivation: Hidden sectors Bottom-up approach to DM: Introduce O(1) new DM fields χ (SM singlet) Why is DM stable? If all renormalizable interactions are allowed. DM would rapidly decay to SM particles

4 Motivation: Hidden sectors Bottom-up approach to DM: Introduce O(1) new DM fields χ Why is DM stable? Lesson from SM: stability = symmetry e - stable due to local U(1) symmetry p stable due to accidental U(1) from nonabelian symmetry Mass scale need not be weak scale. Can be light (< 1 GeV) provided couplings to SM are small

5 Motivation: Hidden sectors Abelian dark force from dark U(1) gauge symmetry: DM + weakly-coupled dark photon Charge conservation stabilizes DM Even if dark photon has mass (spontaneous breaking) Dark photon can be light (sub-gev) Rich phenomenology Indirect/direct detection Collider searches for new gauge bosons Astrophysical probes of structure Arkani-Hamed et al. (2009); Pospelov et al (2009); Forneggo et al. (2011). See Matt Reece s talk Alexander et al. [Dark sectors report] (2016) Feng et al. (2009); Buckley & Fox (2009); ST, Yu, Zurek (2013)

6 Motivation: Hidden sectors Composite DM from non-abelian gauge symmetry Lightest baryon is stable DM due to accidental symmetry (like proton)

7 N F What are DM baryons? For SU(N c ) with N F light fundamental fermions: N c Dark glueballs (no baryons) e.g. Forestell et al. (2016) 1 Dark ρ (J=1) Anthony Francis, R. Jamie Hudspith, Randy Lewis, ST Dark Ω (J=3/2) (J=2) 2 Dark π (J=0) Lewis, Pica, Sannino (2011) Dark nucleons (QCD-like) Bai and Schwaller (2014) Stealth scalar baryons Appelquist et al. [LSD] (2015) Apologies for incomplete references

8 What are DM baryons? Many unknowns: Gauge group: SU(N), SO(N), Sp(N), Number of colors N c Number of flavors N F Representations of dark quarks Masses of dark quarks Chiral or heavy flavor limit? Confinement scale Λ DM Couplings to SM (hidden sector=assume small)

9 What guidance do we have? Stability DM baryons are stable Dark glueballs can also be cosmologically long-lived Minimality

10 What guidance do we have? Relic density If DM baryons annihilate to lighter dark mesons (which decay to SM) then dark baryon mass fixed to be: DM can have a dark baryon asymmetry (asymmetric dark matter) Nussinov (1984) then can have: Other freeze-out mechanisms can also be interesting/relevant Hochberg et al. (2014)

11 What guidance do we have? Stability Minimality Relic density Astrophysical small scale structure Astrophysics can probe hidden sector even if it is completely decoupled from SM

12 Small scale structure issues Astrophysical constraints on DM halos are at odds with collisionless DM predictions Motivates theories with DM self-interactions What is the evidence? What are the implications for composite dark sectors?

13 Beyond the collisionless paradigm Cold collisionless DM N-body simulations (DM-only) predict cuspy density profiles (NFW) No scattering Self-interacting DM (SIDM) DM particles self-scatter elastically in halos Density profiles become shallower (cored profiles) Spergel & Steinhardt (2000) DM density Self-scattering Dark matter self-interactions X X Radius Particles get scattered out of dense halo centers X X

14 Beyond the collisionless paradigm Dark matter and dark forces DM self-interactions can affect distribution of mass inside DM halos through scattering Galaxy Cuspy halo with no interactions Halo with self-interactions (cored profile)

15 Beyond the collisionless paradigm No scattering No scattering DM density Self-scattering Circular velocity Self-scattering Radius Particles get scattered out of dense halo centers Radius Rotation curves reduced (apparent mass deficit in inner halo) Motivation: ΛCDM has small scale structures issues (potentially!) Core-cusp problem/mass deficit problem Moore (1994), Flores & Primack (1994)

16 Core-cusp problem: Inner halo: ρ dm (r) r α Theory prediction: Observations: α 1 (cusp/nfw profile) α 0 (core) Mass deficit problem: Inner halos have less DM mass than predicted from CDM Small scale issues are prevalent in observations: DM-dominated disk galaxies in the field Rotation curves (Dwarf and low surface brightness galaxies) Milky Way satellites Stellar velocity dispersion Massive clusters Stellar dispersion + lensing

17 Rotation curves in spiral galaxies NFW profile SIDM profile Tulin & Yu (in prep); Data from Oh et al [LITTLE THINGS] (2015) Circular velocity (DM + stars + gas): Unknowns: Stellar mass-to-light ratio Mass deficit problem: NFW profile fit to V circ at large radii predicts too-large V circ at small radii

18 Core-cusp problem in Milky Way satellites Two stellar subpopulations are test masses in DM gravitational potential Walker & Penarrubia (2011) Velocity dispersion

19 Mass deficit in massive clusters Cluster Abell 2667 (Hubble Space Telescope)

20 Mass deficit in massive clusters Weak lensing Strong lensing Radius Stellar kinematics in BCG (brightest cluster galaxy) Cluster Abell 2667 (Hubble Space Telescope) Multiple measurements to map dark matter halo in clusters Newman et al (2012)

21 Cored density profile for one cluster Stellar kinematics within brightest central elliptical galaxy Kaplinghat, ST, Yu (2015) Strong and weak gravitational lensing NFW fit to lensing only Baryons

22 Cores seem to be (fairly) ubiquitous Milky Way satellite galaxies Dwarf and low surface brightness galaxies in the field (Rotation curves) Massive clusters Explanations: 1. Failure of DM theory (need to go beyond collisionless CDM) 2. Failure in DM-only simulations to describe real halos in DM+baryons Universe 3. Failure from other systematics in interpreting observations

23 Cores seem to be (fairly) ubiquitous Milky Way satellite galaxies Dwarf and low surface brightness galaxies in the field (Rotation curves) Massive clusters Explanations: 1. Failure of DM theory (need to go beyond collisionless CDM) 2. Failure in DM-only simulations to describe real halos in DM+baryons Universe Very actively debated in the literature! 3. Failure from other systematics in interpreting observations

24 Self-interacting dark matter What scattering cross section value is needed? Rate equation: Figure-of-merit: Typical cross section required to solve small scale anomalies Astrophysics points to dark physics at the MeV-GeV scale But doesn t say how it couples to SM

25 N-body simulation for dwarf galaxy with self-interactions Elbert et al. (2015) Shape of halo depends on cross section (σ/m) σ/m cm 2 /g Form kpc core in dwarf galaxies σ/m < 0.5 Cores too small σ/m >> 50 Gravothermal collapse (Cuspier than NFW)

26 Questions What cross sections are preferred in different astrophysical systems? Fit SIDM halos to dataset of 12 disk galaxies + 6 clusters Get best-fit cross section for each system Kaplinghat, ST, Yu (2015) What are the particle physics implications?

27 Each system is complementary Dwarf galaxy Spiral galaxy Cluster of galaxies Low energies (v/c ~ 10-4 ) Medium energies (v/c ~ 10-3 ) High energies (v/c ~ 10-2 ) Cross section depends on scattering energy. Different size dark matter halos have different velocities.

28 Each system is complementary Dwarf galaxy Spiral galaxy Cluster of galaxies Low energies (v/c ~ 10-4 ) Medium energies (v/c ~ 10-3 ) Like a different particle physics collider with a different beam energy Tevatron (Fermilab) High energies (v/c ~ 10-2 ) TRIUMF LHC (CERN)

29 Cross section for each system Assumption: self-interactions solve small scale issues Galaxies: σ/m 1 few cm 2 /g Clusters: σ/m 0.1 cm 2 /g Average cross section Dwarfs LSB galaxies Clusters Average DM velocity in halo Kaplinghat, ST, Yu (2015)

30 Cross section for each system Assumption: self-interactions solve small scale issues Mock data from simulations with 1 cm 2 /g (to get systematics) Average cross section Dwarfs LSB galaxies Clusters Dark U(1) gauge boson Average DM velocity in halo Kaplinghat, ST, Yu (2015)

31 Particle physics of self-interactions Summary: preferred cross sections Cross section is large Cross section is velocity-dependent Self-interactions for WIMPs? Way too small (and constant for non-relativistic scattering)

32 Proof-of-principle Nucleon self-interactions are in the right ballpark for what is needed for SIDM to work σ(np np)/m p ENDF data Large magnitude and velocity-dependent at non-relativistic energies

33 Self-interactions for composite DM Low-energy cross section σ = 4πa 2 a = scattering length m = DM mass If dimensionful parameters set by confinement scale i.e., then gives right σ/m on dwarf scales

34 Self-interactions for composite DM Require velocity-dependent cross section Naïve condition: Scattering cross section transitions to being velocity dependent when Since v << 1 (DM non-relativistic), require More specifically: Want σ/m to transition at v/c Expect ma 10 3 may provide good fit to galaxies and clusters.

35 Self-interactions for composite DM Either m or a (or both) must be much larger than naïve scaling with Λ DM. Large DM mass (m >> Λ DM ): Heavy flavor dark quarks Example: SU(N) + heavy adjoint fermion (gluino) DM = glueballino (one gluino + glue) m gluino 1 TeV Λ DM 10 MeV Boddy et al. (2014)

36 Self-interactions for composite DM Large scattering length (a >> Λ DM -1 ): Example: nucleon-like DM Cline et al. (2013) Elastic n-p scattering is enhanced due to weaklybound deuteron Note: Fall off at v c/(ma) 5000 km/s Clusters require 0.1 at 1500 km/s E.g. make m DM 10m p with fixed scattering length a

37 Summary If self-interactions solve astrophysical small scale structure anomalies Preferred cross sections Large cross section requires Λ DM < 100 MeV Velocity dependence: Heavy flavors Large scattering length

38 A minimal theory of DM baryons Anthony Francis, R. Jamie Hudspith, Randy Lewis, ST (work in progress) Dark QCD-like theory with N c =2 & N F = 1 Fundamental fermion that is SM singlet

39 Model: SU(2) + N F flavors i i i ij j i i One weird feature of N c =2: Can put quarks and antiquarks in unified multiplet Enlarged chiral symmetry U(N F ) L x U(N F ) R U(2N F ) = SU(2N F ) x U(1) A Chiral symmetry breaking: SU(2N F ) Sp(2N F ) N F =2: 5 Goldstones (baryonic pions) Lewis, Pica, Sannino (2011) N F =1: 0 Goldstones since SU(2) = Sp(2) Unbroken global SU(2) B One would-be Goldstone from U(1) A (gets large mass from anomaly)

40 What is the lightest baryon? Two quark wave function (NR quark model) Ψ = ψ color x ψ spin x ψ spatial antisym x sym (S=1) x sym (L=0) J=1 baryonic mesons Triplet under SU(2) B

41 One flavor SU(2) dark matter Lightest states: Baryonic J=1 triplet ρ=(ρ +, ρ 0, ρ - ) Singlet pseudoscalar state η Superscript = SU(2) B isospin Zeroth order question: Which state is lighter? (In QCD: m ρ <m η ) Relic density story: If m ρ >m η, can have ρρ η η SM

42 Pseudoscalar correlator (connected + disconnected diagrams) Vector correlator Chiral limit Anthony Francis, R. Jamie Hudspith, Randy Lewis, ST (work in progress)

43 Pseudoscalar correlator (disconnected only) Pseudoscalar correlator (connected only) Chiral limit Anthony Francis, R. Jamie Hudspith, Randy Lewis, ST (work in progress)

44 Pseudoscalar mass (disconnected only) Pseudoscalar mass (connected only) Chiral limit Is it plateauing to a constant? (mass from the U(1) A ) Looks like an unphysical Goldstone boson

45 Pseudoscalar mass (connected + disconnected diagrams) Vector mass Chiral limit Anthony Francis, R. Jamie Hudspith, Randy Lewis, ST (work in progress)

46 Conclusions Work in progress: Chiral limit? What is the DM phenomenology? Tentative result: m ρ >m η

47 Backup slides

48 Baryonic astrophysics Does including baryons in simulations solve small scale structure issues?

49 Feedback from AGN in clusters Martizzi et al (2012) N-body simulations with baryons Schaller et al (2014) Feedback leads to a core from initial NFW halo Feedback does not form dark matter cores

50 Feedback from supernovae N-body simulations with self-interactions and baryons CDM+Baryons CDM-only SIDM+Baryons Fry et al. (2015) SIDM-only Vogelsberger et al. (2014) σ/m=10 cm 2 /g σ/m=2 cm 2 /g Bursty star formation (High density threshold for star formation) Smooth star formation (Low density threshold)

51 Diversity problem: challenge for feedback Oman et al (2015) Rotation curve-ology: V max = max velocity Observational proxy for halo mass Central density slope of rising rotation curve Core radius break in slope from rising to flat Similar V max halos can have very different core sizes and central densities Some rotation curves are perfectly consistent with CDM

52 Outliers with large cores Oman et al (2015) Even bursty prescriptions have trouble making cores > few kpc. Example: IC 2574 DM mass deficit within 5 kpc greater than total mass in stars Bursty sims