STAR: Space-Time Asymmetry Research

Transcription

1 STAR: Space-Time Asymmetry Research Testing Lorentz invariance in Low-earth orbit Shally Saraf for the Stanford STAR team October 14,

2 STAR Concept Science 1) Lorentz Invariance Violations 2) Velocity boost c dependence Kennedy-Thorndike Experiment 3) >100x state of the art Lipa, et. al. Prospects for an advanced Kennedy-Thorndike experiment in low Earth orbit arxiv: v1[gr-qc] Science & Technology on Small Satellites Education driven International collaborations Education 1) Graduate & Undergraduate 2) 3-5 year projects 3) Student led tasks Technology 1) Capable small satellite bus 180 kg, 185 W, secondary payload 2) Advanced frequency standards 3) Precision thermal control 2

3 STAR Collaboration Collaborating Institutions Main Contributions ALL Science and EP&O Ames Research Center PM, SE, I&T, and SM&A KACST Spacecraft and Launch Stanford University PI and Instruments to TRL 4 German Space Agency et al Instruments, Flight Clock JILA Instruments to TRL 4 Industrial Partner Flight Instrument Germany German Aerospace Center (DLR) ZARM & Bremen University Humboldt University, Berlin University of Konstanz Kingdom of Saudi Arabia King Abdulaziz City for Science and Technology (KACST) United States NASA Ames Research Center (ARC) Stanford University Joint Institute for Laboratory Astrophysics (JILA) University of California-Davis Industrial partner 3

4 STAR Quad Chart SCIENCE What is the nature of space-time? Is space isotropic? Is the speed of light isotropic? If not, what is its direction and location dependency? Payload to Optical cavities K enclosure I 2 clocks 2 Laser-based comparator BATC is payload consultant Mission design Circular sun-synchronous 650 km circular orbit 180 kg,150 W Launch year lifetime Class D Mission Management NASA Ames: PM, SE, SMA, Mission Operations Stanford: Science and Payload KACST: Spacecraft and Launch DLR: Payload Design & I 2 Clock ALL: Science & EPO 4

5 STAR Technology Advanced frequency standards Optical cavities Molecular clocks f f Hz nano Kelvin thermal control Thermal shields Control algorithms Optical thermometry T F T Inner shield Outer shield F Inner shield Outer shield STAR requires exquisite frequency standards and environmental control, order of magnitude better than current state-of-the-art 5

6 Measuring LIV HOW DOES ONE MEASURE CHANGES IN c? (1) By comparing the length of a rod (measured by light beam) to the rate of a ticking clock rod clock KT coefficient (function v INSTR ) (2) By comparing the length of two rods perpendicular to one another (both measured with a light beam) rod 1 rod 2 MM coefficient (function INSTR ) 6

7 STAR Conceptual Diagram 7

8 Why Measure c Invariance? Colladay and Kostelecky (1997) The natural scale for a fundamental theory including gravity is governed by the Planck mass M P, which is about 17 orders of magnitude greater than the electroweak scale m W associated with the standard model. This suggests that observable experimental signals from a fundamental theory might be expected to be suppressed by some power of the ratio: r m M W P ~ The STAR sensitivity could close the gap! 8

9 Kinematic approach to LIV Considers only light beams and ideal rods, clocks: If a laboratory is assumed to be moving at a velocity v relative to a preferred frame, the speed of light as a function of the angle relative to the velocity vector is given by c( )/c = 1 + (1/2 - b + )(v/c) 2 sin 2 + (b - a - 1) (v/c) 2 where a is the time dilation parameter, b is the Lorentz contraction parameter, and tests for transverse contraction. (SR: a = -1/2; b = 1/2; = 0) Michelson-Morley : -dependent term Kennedy-Thorndike : -independent term - Mansouri and Sexl (1977) Simple but incomplete! 9

10 Lorentz violations in the SME Subset of Lorentz and CPT violating Standard Model Extension (SME) - Colladay and Kostelecky Considers small violations that are potential remnants of Planck-scale physics - subset considers Lorentz-violating quantum electrodynamics - restricting to photon sector and renormalizable terms - reduces to Maxwell equations plus two Lorentz-violating terms: - one term CPT-odd(breaking), the other CPT-even(preserving) - CPT-odd term known to be very small from radio galaxy polarization data - CPT-even term less well-known Model has analogy with electrodynamics in a homogeneous anisotropic medium - has links to Mansouri and Sexl kinematics, and relates to THεμ -19 free parameters, 10 constrained by astrophysical observations - Optical cavities sensitive to other 9 parameters - Kostelecky and Mewes, 2002 Extended: Kostelecky & Mewes,

11 MM and KT as subsets of the SME highly simplified example (K&M 2009): rods and clocks have effective metrics with Lorentz violating parameters: c clock, c rod obtain b + - 1/2 = 7/12(c rod ) 00 a - b +1 = - 7/12(c rod ) 00-5/12 (c clock ) 00 (MM style) KT style) => KT measurements don t reduce to MM measurements except in special cases => MM and KT relate to the fermion sector (?) 11

12 LV species-dependent fields (experiments need to specify species involved) Turns out, precision length control of cavities is very hard and bulky. Can we use two narrow transitions and do KT? 12

13 First modern MM experiment Brillet and Hall, PRL

14 Improved MM experiment Crossed-cavity MM experiment Peters,

15 The problem with g What about Horizontal Accelerations? Horizontal expect a reduction but Observed Sensitivity ~ 1 x (Tilt effect linear in angle) Better? Airy Points? Vertical Max Sensitivity but Symmetry reduction ~200 x (Tilt effects only quadratic) There may be better cavity support ideas? 15

16 Frequency/acceleration sensitivity 10 MHz/ ms -2 a = 0.11 * L khz/ms khz/ms -2 a = 0.577* L a L 16

17 STAR mission characteristics ESPA compatible secondary payload on an EELV launch Circular sun-synchronous ~ 650 km orbit Launch year mission lifetime 17 17

18 Orbital Motion Sun Earth Sun-synchronous orbital motion of STAR instruments 18

19 STAR KT-Style measurement 19

20 Modern KT style test configuration clock based on length standard clock based on atomic transition beat measurement with varying laboratory velocity 20

21 Why KT in Space? Kennedy-Thorndike signal enhancement Signal modulated at satellite orbital variation ~1.5 hr Signal modulated at orbital velocity differences 7 km/s Diurnal Earth rotation signal < hr Yearly Earth orbital motion signal at hr Disturbance reduction Microgravity Seismic quietness Relaxed stress due to self weight Far away from time dependent gravity gradient noises KT Improvement in Space: Faster signal modulation 4 ( 16) Higher velocity modulation 20 to 30 Other considerations ~ 1 to 3 Net Overall Advantage

22 KT History KT coefficient History of KT measurements R.J. Kennedy E.M. Thorndike STAR Year 22

23 STAR schedule, cost and status Schedule Cost Three-year development Two-year operations Payload: ~ $ 50M Total Mission: ~ $140M Concept first proposed as a MOO 2008 SMEX Second proposal submitted in Review pointed out some weaknesses Science, TRL levels Current efforts: Bring instrument to TRL 5 Using internal resources Contributions from partners Mitigate weaknesses of 2011 proposal 23

24 STAR Optical Setup & Noise Budget Error Source KT MM Optical Cavity thermal expansion (0.1microK temp. stability, 10 9 CTE) Optical Cavity mirror thermal noise (loss < 10 6 ) Optical Cavity residual gas pressure Optical Cavity shot noise (locking) Optical Cavity satellite spin rate stability (Δω/ω < 0.025) Optical Cavity satellite pointing knowledge (0.5 deg) Total Molecular Clock N/A Frequency Shifter (comparator) Total Error at measurement frequency with 2 clocks Total Random Error after 2 year integration time (Δc/c) MARGIN 30% 70% 24

25 Optical cavity Key optical cavity parameters: L/L < at orbit and harmonics with 2 years of data L/L < at twice spin period with 2 years of data ULE cavity block (4 cavities@ 45 deg) Derived requirements: Expansion coefficient: < 10-9 per K Operating temperature: within 1 mk of expansion null (~ 15 C nom) External strain attenuation: > Stiffness: L/L < 10-9 per g, 3-axis Implied material: ULE glass Optical couplers Support structure Thermo- Mechanical isolators 25

26 Iodine Reference Vortrag > Autor > Dokumentname > Datum 26

27 Atomic reference Next steps: set up of a compact Iodine standard multi-pass cell baseplate made of Zerodur (for space- qualification and pointing stability) Using s.q. AI-Technology (HTWG Konstanz / EADS Astrium) Investigate resonantly enhanced interaction in a short cell (Stanford) Vortrag > Autor > Dokumentname > Datum 27

28 State of the art: Iodine vs. cavity Thermal noise floor of cavities STAR Orbital period Vortrag > Autor > Dokumentname > Datum 28

29 Thermal enclosure Main Requirements: Thermal stability Stress attenuation Launch and space compatible Thermal performance: Cavity L/L < (2 yr data) at: - orbital period and harmonics - twice spin period Derived requirements (2 yr average): Thermal stability of 10-8 K at orbit Thermal gradient ~ 10-9 K/cm at orbit Maintain cavities temperature to 1 mk Multi-can structure 29

30 Thermal modeling of enclosure 30

31 Strain attenuation model - FEA Estimated strain attenuation: > 10 3 per can Extrapolating to entire enclosure: > Exceeds requirement by x

32 Fundamental frequencies The first mode of the assembly was found to be 77 Hz First lateral mode: 77.6 Hz First axial mode: 93.9 Hz 32

33 Optical Coupling System Laser, Optical Bench Absolute Reference Length Reference Optical Fiber Function Box Laser, Optical Bench Absolute Reference Thermally Stabilized Fiber Conduit Control Electronics 33

34 STAR mission characteristics ESPA compatible secondary payload on an EELV launch Circular sun-synchronous ~ 650 km orbit Launch year mission lifetime 34

35 Optical cavity work at Stanford 1550nm 1064nm 35

36 Vibration insensitive optical cavities STRAIN DISTRIBUTION Zero relative displacement at the ends of the optics axis Static Load applied at the points marked on the perimeter 36

37 Iodine MTS setup at Stanford Arie & Byer, line R(56)32-0 is interesting Lock laser to the a 10 HFS Sub-doppler detection Modulation Transfer Spectroscopy (MTS) Natural Linewidth ~ 400KHz Broadened line < 1MHz Investigate narrower lines at ~516nm 37

38 Iodine setup at Stanford 38

39 CUBESAT concept for technology testing Motherboard, CPU, Radio 3U cube sat chassis PDH, counter boards Thermal enclosure for optics Spherical optical cavity Thermal enclosures for cavity Electrical power system w/ batteries (30 W hr) AOM x2 Cobolt nm laser Circulator Iodine cell (2cm long) Optical bench 39

40 ATOMIC REFERENCES FOR KT nominally isotropic systems: I 2, CO, C 2 H 2 etc very narrow linewidths -> excellent frequency stability relaxed environmental control relative to cavities access various LIV coefficients in fermion sector technical issue is making a beat note between two systems Femtosecond frequency combs could bridge the gap. - But to fly a frequency comb on a satellite is still a challenge.. 40

41 Lorentz Symmetry & Lorentz Violations STAR: Search for a Lorentz violation at the level of to A factor of 100 to 300 better than ground experiments Both orientation & velocity dependent violations LORENTZ SYMMETRY & LORENTZ VIOLATIONS Time dilation: equal clocks tick at different rates Length contraction: equal rods have different lengths Lorentz violations would exist outside of a universal preferred reference frame, the only frame in which c is truly isotropic 41

42 Questions? Other possibilities for violations: Birefringence of pulsed light Cosmic rays Spectroscopy of anti-matter Gamma ray dispersion Neutrino oscillations Spin dependent effects Kostelecky, Scientific American,