Download mini-STAR on a small satellite

mini‐STAR
on a small satellite
Iodine vs cavity comparison
in space
J. Lipa
Nice, 2013
NASA Science Plan for 2007-2016:
The #1 astrophysics research objective is to:
“Understand the …nature of gravity”.
The first two Baseline Objectives for Astrophysics are:
1. “Test the validity of Einstein’s GR “
2. “Investigate the nature of space-time through
tests of fundamental symmetries; (e.g., is the
speed of light truly ISOTROPIC?)”
Experimental foundation of Special Relativity:
Robertson, Rev. Mod. Phys. 1949
Kinematic approach to Lorentz violations:
Assumptions:
•
Considers only rods, clocks and light beams:
• Assumes a ‘preferred’ inertial frame in which there are no Lorentz violations
• Considers a moving frame in which violations can occur
Experiment:
a laboratory is 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
If
c()/c = 1 + (1/2 -  + )(v/c)2sin2 + ( -  - 1) (v/c)2

 is the time dilation parameter,  is the length contraction parameter,
and  tests for transverse contraction. (SR:  = -1/2;  = 1/2;  = 0)
where
Analysis:
•
Michelson-Morley : -dependent term
•
Kennedy-Thorndike : -independent term
- Mansouri & Sexl (1977)
- Robertson (1949)
Kennedy- Thorndike Experiment:
Kennedy
mSTAR Mission Objectives
Thorndike
Measure the boost anisotropy of the velocity of light to 10-18
 Derive the KT coefficient to the corresponding resolution, ~ 7x10-10
Science Background
Experiment Description
To perform the KT experiment mSTAR replaces
one of the arms of a MM interferometer with a
molecular transition in iodine as a reference.
By moving to space mSTAR takes advantage of
the much higher orbital velocity and faster cycle
time when compared with ground based
experiments.
mSTAR will gain a factor of 100 improvement
over the best KT measurement to date.
The Kennedy-Thorndike (KT)
experiment tests for a velocity
dependence in the speed of light.
It used a similar interferometer to MM,
but one arm was much longer than the
other. Alternatively, an atomic clock
can be used for one arm.
This makes it sensitive to the distortion
of time with velocity, which could affect
the speed of light.
If an effect is found, it would again
force the rewriting of the laws of
physics and revise our understanding
of the early Universe.
Generation of sinusoidal KT signal
from orbital velocity
Readout Description
As mSTAR orbits the Earth, the velocity of the spacecraft varies with respect to the cosmic microwave
background frame.
If the speed of light has a dependence on the velocity relative to the reference frame, it would cause a change
in the resonant frequency of the high-finesse cavities. This signal would occur as a sinusoid at the orbital
period of mSTAR, TKT above.
History of KT resolution
For the KT experiment mSTAR compares the frequency of one high-finesse cavity with the wavelength of a
laser stabilized to molecular iodine as an absolute frequency or clock reference. Other experiments have
shown atomic transition frequencies to be independent of velocity to very high precision.
Michelson Morley Experiment:
mSTAR MM Objectives: Secondary
Measure the anisotropy of c to 10-17
Derive the MM coefficient to ~ 1.210-11
Derive the generalized coefficients of LIV
• boost independent: < 6x10-17
• boost dependent: ~ 10-13
Readout Description
Compare the resonant frequencies of an
optical cavities with aniodine reference
Signal at 1/2TMM (TMM = 2 – 20 min)
Configuration conceptually similar to MM
A. A. Michelson
E. W. Morley
Lorentz violations in extensions of the Standard Model:
•

•
A general Lorentz-violating extension of the Standard Model (SME) is
being developed by Kostelecky and co-workers

It covers potential violations for photons, fermions and bosonic
components of matter and is more general than, but consistent with
the kinematic approach
•
Because of its general nature, it contains many parameters, so far >120
•
This gives rise to a wide variety of interesting experimental tests, from
light polarization studies of quasars to cavity and clock experiments
to analyses of high energy particle experiments and cosmic rays



•

Any violation observed would be considered a clue to understanding
Planck-scale physics and the details of the Big Bang
STAR will improve estimates ‘classical’ kinematic parameters
& groups of new SME parameters
Photon sector Lorentz violations:
Restricting






Lorentz violations to the photon sector:
- subset considers Lorentz-violating quantum electrodynamics
- restricting to renormalizable terms
- reduces to Maxwell equations plus two Lorentz-violating terms:
- one term CPT-odd, the other CPT-even
- 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 TH model

-19 free parameters, 11 constrained by astrophysical observations

- Optical cavities sensitive to other 8 parameters

- Kostelecky and Mewes, 2002
Frequency shift for a single cavity:
- Kostelecky and Mewes, 2002
More general cavity effects in SME:
Resonant frequency of cavity:
f = nc/2L
L: cavity length, n: mode number, c: velocity of light
Lorentz violations can affect both c and L
 Both photon sector (c) and fermion sector (L) are involved
 Sensitivity to fermion coefficients of violation is material
dependent
 3 extra coefficients for isotropic materials
- Mueller, 2005
Expansion of sine coefficients in data fit:
- Kostelecky and Mewes, 2002
Kinematic approach vs. SME:
•
Kinematic approach is more restricted than the SME approach
•
assumes the existence of a preferred frame, not allowed in the SME
•

mapping onto SME implies that MM type experiments measure photon
and fermion parameters
•
KT experiments measure fermion parameters
•
Kinematic model assumption of ‘universal’ parameters , ,  must be modified
to rod and clock-specific parameters

•

Implies different types of rods and clocks needed to cover the many parameters
involved
Atomic clocks and the SME:
The SME part:
i.e. there are ‘only’ about 35 SME
parameters relevant to an atomic clock
- others involve quarks, gluons, etc.
A component of the clock frequency shift:
Molecular clocks and the SME:
• Molecular clocks not yet studied within the SME
• For lines involving electronic transitions (Iodine), analysis expected
to be similar to atomic clock case
• Pure roto-vibrational transitions (CO) will need some new analysis
- fermion effects change separation of nuclei
• SME coefficients expected to be entirely in the fermion sector
• Sensitivity to coefficients of violation will be species dependent
COBE Cosmic Microwave Background Data (1989)
Detected:
• Uniform microwave background
• Dipole signal from velocity
• Background fluctuations:
‐ Galactic contribution
‐ Deep space contribution
WMAP CMB data (2001)
Planck CMB data (2009)
Planck CMB data analysis (2013)
Upper: the derived quadrupole (temperature range ±35 micro‐K). Lower: the derived octopole (temperature range ±35 micro‐K). Cross and star signs indicate axes of the
quadrupole and octopole, respectively, around which the angular momentum dispersion is maximized.
‐Planck collaboration, arXiv, 1303.5083v1
STAR Geometry and Frequencies:
KT signal: orbit & orbit  Earth
MM signal: 2spin & 2spin  2Earth
•
•
•
 spin = 1/(100 sec)
 orbit = 1/(98 min)
 Earth = 1/(1 yr) Spacecraft spin rate (nominal):
Orbit: 600 km Sun‐sync (nominal):
Earth’s orbital rate:
= 10 mHz
= 0.17 mHz
= 32 nHz
STAR


spin
Earth


orbit
Sun
650 km
1 Au

Earth
Sun-synchronous orbital motion
Sun
Earth
mSTAR Data Analysis Overview:
•
Data analysis goal:
– Estimate fractional change in velocity of light (c/c) as function of velocity (KT) and orientation (MM) in inertial space relative to ‘preferred frame’ to 10–17
•
Two types of analysis:
1. Assume preferred frame is the CMB frame (Primary)
– vCMB = 377 km/sec (relative to the Sun), RA = 11.2 h, dec = –6.4 deg
2. Assume preferred frame is unknown and search in all directions (Secondary)
•
Kinematic data analysis model:
c/c = A (v/c)2 sin2 + B (v/c)2
c : nominal speed of light
v : spacecraft absolute velocity relative to preferred frame
 : angle between cavity and v
A : constant MM parameter to be estimated
B : constant KT parameter to be estimated
mSTAR Science Data Analysis:
•
•
Primary science signals
– KT: Beat frequency between iodine and optical cavity at orbital rate
– MM: Beat frequency between optical cavity and iodine at roll rate x 2
Secondary science signals
– Spacecraft orbit (e.g. from GPS)
 Differentiated to produce time history of spacecraft velocity vector
– Spacecraft attitude (e.g. from star tracker)
• Spin axis orientation • Spin phase
•
Primary analysis approach
– weighted least square fit of KT & MM coefficients (multiplying appropriate time signatures)
– Zero‐frequency offset & expected low frequency drift also simultaneously fit
– Additional fits to detemine groups of SME parameters
•
Secondary approach
– Same as primary, with additional fit parameters defining direction & velocity
of preferred frame
Possible mSTAR cavity design
(GRACE‐FO)
Ltop
Deflection of cavities with acceleration:
worst case lab accelerations: ~ 10-3 ms-2 at 30 Hz vertically
Horizontal
deflection
per ms-2
4 nm
a
0.8 nm/div
-4 nm
a
Vertical
deflection
per ms-2
~ 200 kHz/ms-2
Lbottom
21 nm
0.5 nm/div
25 nm
 Short cavity
 Support near
geometrical center
for CMRR
 Vertical orientation
for symmetry
 DLcavity ~ pm
Iodine Frequency Reference on EBB Level:
25cm
55cm
Spectroscopy Unit,
Braxmaier et al, 2013
Iodine Molecular Clock data
fcw
2fcw
Comparing optical clock
against other RF clocks
Ye, Ma, Hall, PRL 87, 270801, 2001
Cavity thermal control:
Multi‐stage thermal filtering can give excellent control even for an equatorial orbit.
miniSTAR would need less layers for similar control.
Double conical optical cavity within UV-LED footprint
STAR mission characteristics:
 ESPA compatible secondary payload on an EELV launch
 Circular sun‐synchronous ~ 650 km orbit  Launch 2015‐2016
 2‐year mission lifetime
Rendering of STAR spacecraft
Nominal Mission Outline:
Mission duration:
2 years
Orbit:
LEO, 600 km
Inclination:
~98°, sun synchronous, 0600
Spacecraft attitude:
sun pointing spin axis
Spin rate:
1 - 10 mins per revolution
Launch configuration: secondary payload
Launch date:
2017
Communication:
twice per orbit average
Science ops.
Timeline:
Instrument turn-on
Sun acquisition
Pointing stabilization
Spacecraft spin
Thermal stabilization
Beat note acquisition
Beat note and housekeeping readout
Health-check monitoring
Fail-safe recovery (as needed)
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, 2002