Synergizing Screening Mechanisms on Different Scales

Transcription

1 Synergizing Screening Mechanisms on Different Scales Jeremy Sakstein University of Pennsylvania Probing the dark sector and general relativity at all scales CERN 17 th August 2017

2 Or. What should astrophysical tests of gravity mean to you? Jeremy Sakstein University of Pennsylvania Probing the dark sector and general relativity at all scales CERN 17 th August 2017

3 Two views of MG 1) Strong field: Want UV modifications of gravity Higher-order operators Typically satisfy SS bounds Look for deviations from GR in strong field regime

4 Two views of MG 2) Cosmologists: Want IR modifications of gravity Relevant for cosmology but ruled out by SS bounds Use screening mechanisms to hide modifications in SS Natural suppression of deviations Don t need to tune parameters

5 Screening mechanisms Non-linear effects decouple cosmological scales from the solar system solar system astrophysics cosmology screened partially screened unscreened

6 Some inconvenient truths about screening mechanisms Highly-non-linear field equations Can t use PPN Well-posedness? Do we care (EFT)? Two-body/low symmetry systems? Need novel tests Complex modelling for laboratory tests Novel astrophysical probes

7 Astrophysical probes - mildly screened regime Cepheid stars Dwarf stars Galaxy clusters White dwarf stars Black holes Neutron stars

8 The problem with MG Newtonian limit of GR: r 2 N =4 G F N = r N Modified gravity new scalar graviton: r 2 =8 G F 5 = r F 5 F N =2 2 solar system: 2 2 < 10 5 (Shapiro time-delay effect, Cassini)

9 Screening mechanisms Two options: r 2 + F 2,...)=8 G + V 0 ( ) Non-Poisson kinetic terms Vainshtein screening Kill off the source no scalar gradient chameleon/symmetron/f(r)

10 Chameleon screening Add a scalar potential: r 2 =8 G + V ( ), Get these to cancel out dynamically

11 Chameleon/Symmetron/f(R) R r 2 =0 r s r 2 =8 G

12 Chameleon/Symmetron/f(R) R r 2 =0 r s r 2 =8 G

13 Vainshtein screening Change kinetic terms e.g. cubic galileon: apple 1 r 2 d dr 2 r r2 c 3 r 02 =8 G Poisson term Galileon term Coupling to matter (crossover scale r c )

14 Vainshtein Mechanism We can integrate this once: - Vainshtein radius

15 Vainshtein screening

16 Vainshtein screening is generic DGP braneworld gravity Covariant galileons Massive gravity Massive bi-gravity VERY generic scalar-tensor theories with three D.O.F Horndeski Beyond Horndeski breaks down inside objects

17 ( PPN = 1) Unscreened Screened

18 Vainshtein breaking in beyond Horndeski Inside objects: F grav = GM(r) r 2 + 1G 4 d 2 M(r) dr 2

19 VERY important parameter THE ALPHA PARAMETERS E.g. for the simplest case (one new scalar d.o.f): T (t) : c 2 T =1+ T speed of gravitational waves,. K (t) : kinetic term of scalar field. B (t) : `braiding mixing of scalar + metric kinetic terms. M (t) = 1 H d ln M 2 (t) dt : running of effective Planck mass. H (t) : disformal symmetries of the metric. Credit: Tessa Baker

20 VERY important parameter 5 functions that control linear cosmology (EFT of DE) NR probes combinations of three of them: 1 = 4 H 2 c 2 T (1 + B) H 1 Constraining these constrains cosmology!

21 Outline of this talk Chameleon/symmetron/f(R) Cepheid stars Vainshtein/galileons supermassive black holes Beyond Horndeski dwarf + neutron stars

22 Chameleon/symmetron/f(R) Two parameters: r s - strength of fifth-force r 2 =8 G (fully unscreened) - self-screening parameter (f R0 =2 0 /3) object is unscreened if

23 Astrophysical screening main-sequence post-ms dwarf galaxy Need void dwarfs due to environmental screening

24 Complication: environmental screening Can only use unscreened dwarf galaxies in voids! Screening map of SDSS data: Cabre et al. 2012

25 Chameleon stars MESA 2 2 =1/3 A new and powerful tool to compare with observations

26 Testing chameleons using stars Parameters probed using distance indicators Need a formula to relate observational data to distances

27 Test using distance indicators Main idea: Distances measurements assume theory of gravity Different methods should agree Compare distances to unscreened galaxies E.g. Luminosity distance: d 2 L = L 4 F

28 Cepheids Period-luminosity relation T / G 1/2 Cares about gravity: d d = 0.3 G G

29 Tip of the red giant branch Peak luminosity is fixed - standard candle Set by nuclear physics - independent of gravity

30 Distance indicators

31 New constraints Jain, Vikram, JS (2012) Excluded f(r)

32 Burrage, JS 16 The big picture V e = 4+n n + M pl = = M Pl M n =1 Astrophysics can t do better than this

33 Negative n is also a chameleon! = ev Chameleon relevant for cosmology F (R)lives here

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35 Symmetron/Chameleon/f(R)/photon coupling 0 Eȯ. t-wash µ = ev Atom Interferometry V e = µ2 2 1 µ 2 M 2 s Astrophysics

36 Galileons Self-acceleration (DE but does not solve CC) Nice UV properties Massive gravity Braneworld models Hard to test due to Vainshtein screening

37 Hui & Nicolis 12 No hair theorem Black holes described by mass and spin only! No galileon charge Q so BH does not feel galileon force Matter has Q = M Matter and BH fall at different rates Violation of the strong equivalence principle

38 Hui & Nicolis 12 Eötvös experiments with black holes

39 Galaxy clusters: nature s leaning towers BH

40 NFW, c=5 M = M Virgo Cluster (km/s) 2 /kpc r V ndgp Newtonian Galileon (r c = 500 Mpc) Galileon (r c = 6000 Mpc) -- RMS Cosmological self-accelerating

41 Offset Offset kpc ρ = 0.05M pc -3, M 200 = M ρ = 0.1M pc -3, M 200 = M -- ρ = 0.1M pc -3, M 200 = 2x10 14 M Mpc

42 M 87 JS, Jain, Heyl, Hui APJL 17 /(1000 km) -1 self-acceleration LLR M 87 /Mpc 3 = 6M p /r 2 c 1/3

43 Future tests This is one galaxy! More galaxies SDSS, DES, Euclid + X-ray/Radio Morphological distortions Missing SMBHs!

44 Tests of beyond Horndeski Unscreened Screened

45 Tests of beyond Horndeski F grav = GM(r) r 2 + 1G 4 d 2 M(r) dr < 1 < 1 Gravity weaker than GR! No stable stellar configurations Saito et al. 2015

46 Dwarf stars - a new test of gravity Red dwarf

47 Dwarf stars - a new test of gravity Perfect tests: Chemically and structurally homogeneous Equation of state is well-known Lots of interest in low mass objects (KEPLER, GAIA)

48 Low mass M-R Red dwarf Brown dwarf MMHB

49 Red dwarfs MMHB Hydrogen burning when core is hot and dense enough Gravity weaker Core cooler and less dense at fixed mass Higher MMHB

50 Red dwarfs MMHB Stable burning when production balances loss L HB = L e : M MMHB =0.08 ( 1 ) ( 1 = 0) M Proton burning EOS + theory of gravity

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52 New constraint Lowest mass star is Gl 886 C M = ± M ) 1 < JS, PRL (2015)

53 Neutron stars Mass Sun Radius few km Mass, spin, charge, quadrupole moment,, hair! Relativistic: v/c 1

54 Testing GR with neutron stars Angular velocity! No rotation mass-radius relation O(! ) moment of inertia O(! 2 ) tidal Love number/quadrupole moment

55 Babichev,, JS 16 Can we test Vainshtein with this? Larger maximum mass Devil is in the detail Most massive NS observed Larger radii

56 Equation of state is unknown!

57 Breu, Rezzolla 16 Need EOS-independent tests Moment of inertia

58 We can do this for BH

59 Modifications are larger than the scatter

60 Credit: Alessandra Bounanno This measurement is 10 years away! Need specific systems to decouple spin-orbit coupling Complication: rotation effects scalar at O(! 2 ) but not O(! ). Lose integrability.

61 Summary novel astrophysical probes Chameleons/symmetrons/f(R): Test using distance indicators Astrophysical region nearly saturated Vainshtein: SMBHs normal branch in trouble Can push to self-accelerating with future surveys Beyond Horndeski: Directly constrains cosmology Dwarf and neutron stars promising probes