Fulvio Ricci - PowerPoint Presentation

Slide1

Fulvio Ricci

Dipartimento di Fisica Università di Roma La Sapienza& INFN Sezione di Roma

Napoli 2 Aprile 2014

Experimental GravitationSlide2

Theoretical motivations

supporting the new deal of experiments in GravitationSlide3

Gravitation and the other fundamental interactions

Fundamental InteractionCrucial years FundamentalconstantNormalized Intensity Gravity1687Gmp2/hc5.1x10-39

Weak nuclear force1934

GFermi (m

pc2

)2

1.03x10

-5

Electromagnetism1864e

2/(4 p

eo

hc)7.3x10

-3 ~ 1/137

Strong nuclear force

1935/1947

a

s

0.119Slide4

The open question

Why the weak force is 1032 times stronger than gravity? This is the hierarchy problem.Many theoretical physicists have devoted significant fractions of their careers to trying to solve this problem:new particles and new forces are needed (supersymmetry, technicolor , little Higgs, etc.) ?gravity is mistaken? Do they exist new unknown dimensions (“extra dimensions”), where the gravity strength leak off?If extra dimensions exist, they could be as big as a millimeter and no experiment would have detected them!In any case Gravity itself would be only way to solve the mistery "seeing" for example these extra dimensions. Slide5

The Dirac large number hypothesis

Electric /Gravity force ratio between an electron and a proton N1 = e2 /(4 p eo G me mp) ~ 2x1039 (Universe horizon ) / (Classical electron radius) ratio

N2 = (c Ho-1

)/[e2 (4

p

eo m

ec2)

-1] ~ 5x10

40 (Ho-1 

is the Hubble time 68 km/s/Mpc ~ 1.4

x 1010 years)

the coupling constants are not…….. any more constant

The two numbers are nearly coincident,

N1≈ N2

and, since the Universe is expanding,

if

this numerical coincidence is ALWAYS verified

G=G(t) or a=

a

(t

) Slide6

Do they change with energy converging to a common value ?

Standard ModelSuper-simmetric ModelStrongWeak

E. M.Strong

Weak

E. M.

Source: David Kaplan

>1O

16 GeV

 not far to the Planck scale where the Gravity is crucialSlide7

Cosmology

The Big Bang associated to the inflationary scenario, a rapide expansion between 10-33 and 10-35 s, at present is the dominant theory of the creation of the universe:Baryongenesis happened in an epoch before inflation, when CP violation mechanism prefer matter to antimatterQuarks and anti-quarks combined at 10-5 s. Nucleosynthesis started at about 3 min.380,000 years neutral atoms started to form and matter and radiation were separated ( decoupling)Slide8

Cosmology and Great Unification Theory

Forces unified Time Length[m]Temperature [GeV]1 GeV  1.2 1013

KIn principio erat verbum

Gravity, Strong, Weak and E. M. forces

0

0

∞

Gravity decoupled

Nuclear, Weak and E.M forces 10-43

[s]

10-35

1019 Strong force

decoupled Weak and Electromagnetic forces

10-35

[

s

]

10-2710

14Weak interaction decoupled

All interaction

splitted

in Nature

10

-11

[

s

]

10

-3

10

2

Present universe

“” “” “”

10

10

[

y

] - 3 10

17

[

s

]

10

2610-12

The Planck Erascale

W.& EM. un. tested

@

LEP&LHCSlide9

Does Cosmology challenge GR?

Experiments in laboratories have confirmed that on Earth GR is valid to extremely high precision. Moreover, peculiarities about the orbits of Mercury (perihelia shift) or pulsars are very well explained with GR. On the other hands Cosmic Microwave Background (CMB) in 1965 confirmed a key prediction of the Big Bang Cosmology. Then, the observation of CMB anisotropies supported the inflationary scenario, i.e. that quantum fluctuations in the microscopic inflationary region, magnified to cosmic size, become the seeds for the growth of structure in the universeHowever, GR alone fails in describing structures as cluster of Galaxies and Galaxies: we need an extra mass, the gravitating dark matter, to stabilize the observed structures. CMB measurements show that just the 4.5 % of the universe content is ordinary matter while we need the 28% of gravitating matter to fit data (dark matter particles interact only through gravity and possibly the weak force).Moreover, the expansion rate of the universe measured by observing the distant galaxies and supernovae push toward the hypothesis of the existence of a

negative pressure (dark energy), related to the vacuum energy: it should contribute to the GR stress-energy tensor causing the accelerating expansion. Slide10

The cosmological standard model

A pure GR approach, as presented and accepted by A. Einstein, is not sufficient to explain the modern cosmological observationsA standard cosmological model has to include dark matter and an expanding universe: the present standard model is LCDM.The model assumes a scale invariance in the spectrum of primordial perturbations and describes a universe without spatial curvature. L is the cosmological constant ( firstly introduced by Einstein and then rejected by himself). It represents the vacuum energy, which would explain the accelerated expansion of the universe and constitute 70% of the energy density contained in it.Slide11

ΛCDM success and….weakness

ΛCDM describe successfully the large scale structure of the Universe and it predicts the existence of the baryon acoustic oscillation feature, the CMB polarization and the statistics of the weak gravitational lensingThe model is based on six parameters, which are estimated by matching the model with the cosmological observations. However, LCDM does not explain the nature of the dark matter and the dark energy field;it is in contrast with other experimental evidences as for example

the central density profile of galaxies, the luminosity of dwarf galaxies: in hydro-dynamical simulations it is almost two orders of magnitude higher than expected for haloes of this mass,- etc., etc,…………………….Slide12

Alternative approaches

L is an energy density in an expanding Universe. As consequence the energy is not conserved in this model, and we are pushed to postulate that the Universe may not be an isolated system, i.e. it should exist a “Dark Side” of the Universe. (The cosmologist J. A. Peackock

is used to say: <<Vacuum should act as a reservoir of unlimited energy, which can supply as much as is required to inflate a given region to any required size at constant energy density.>>)MoND

( and Mond+):

F= m

m(a/ao) a (ao

~10-10 m/s

2 and m(a/a

o)  1 for a/ao

 ∞)

f(R) gravity: family of generalized GR theories, each one with a different assumption on the structure of the Ricci scalar

Tensor-Vector Theories (TeVeS):

equivalent to MoND in the non-relativistic limitString cosmology:

orginated by G. Veneziano, open the door even to a pre-big bang scenarioSlide13

Beyond General Relativity: how to get experimental evidence?

GR experimental proofs are all related to the case of very weak limit In the near future the strong regime will be explored by detecting Gravitational Waves.Gravitational waves may contain direct signatures of the universe’s inflationary period ( see BICEP2!) or of the electroweak phase transition or ultimately may present direct traces of quantum gravity.A complementary approach, emerged as one of the most rapidly growing subfields of modern physics, is to carry on precision laboratory tests of gravity.Laboratory and space-based experiments are designed to test the foundations of General Relativity and to probe theories that predict deviations from General Relativity. The starting point: GR is a complete gauge theory based on the assumption of Einstein Equivalence Principle (EEP)

New physics can be hidden beyond the violation of this assumption Slide14

The Einstein Equivalence Principle (EEP)

Local Lorentz Invariance (LLI): The result of any non-gravitational experiment is independent of the speed of the apparatus (in free fall)Local Position Invariance (LPI): The result of any non-gravitational experiment is independent of where and when it is brought to completion in the Universe.Universality of Free Falling (UFF or WEP): If an uncharged test body is placed at an initial event in space-time and given an initial velocity there, then its subsequent trajectory will be independent of its internal structure and compositionEach experiment, devoted to falsify one of these assumptions, is classified as an effort to search for new physicsSlide15

The way to classify and compare experimental results

The experiments challenging the EEP are compared using two different approaches:Standard Model Extension (SME). This is an approach aimed by the particle physicists. It is the generalization of the usual Standard Model and General Relativity allowing for violations of Lorentz and CPT symmetry. The violation is controlled by a set of coefficients whose values can be determined or constrained by experiment. (Colladay, D., and V. A. Kostelecky ́, 1997, Phys. Rev. D 55, 6760. Colladay, D., and V. A. Kostelecky ́, 1998, Phys. Rev. D 58, 116002.)The Parameterized Post Newtonian (PPN) formalism is an approach aimed by the gravitational physicists. The PN expresses Einstein’s equation of Gravity in terms of the lowest-order deviation from the Newton’s law. In the PPN formalism a set of parameters are defined, in which a general theory of gravity can differ from GR gravity. This theoretical frameworks held in the case of weak field limit (see Will, C. M. Theory and Experiment in Gravitational Physics, University Press, Cambridge, 1993)

The two approaches don’t communicate so well each other !!!Slide16

Summary tables of the SME coefficients

Nine properties tables are provided, listing various features and definitions related to Lorentz violation.4 tables concern the terms in the restriction of the minimal SME to quantum electrodynamics (QED) in Riemann spacetime.2 tables contain information about the matter sector and the gauge and gravity of the minimal SME in Riemann-Cartan spacetime. 1 table summarizes some features of the coefficients for Lorentz violation in the neutrino sector. 2 remaining tables provide information about the operator structure and the spherical coefficients for Lorentz violation in the non-minimal photon sector.V. Alan Kostelecky and Neil Russellin REVIEW OF MODERN PHYSICS, VOLUME 83, JANUARY–MARCH 2011tabulates measured and derived values of coefficients for Lorentz and CPT violation in the standard-model extension.Slide17

The PPN parameters and their physical meaning

The original parametesThe new notation introduced by C. Willa1=7D1+D

2-4g-4; a2=D

2

+z-1; a3

=4b1

-2g-2-z

z

1=z; z

2=2b-2b

2-3g-1; z

3=b

3 - 1

10x=3h-12b+3g+9+3a

1

-2a

2

+2z1

+z2(

x

=0 for GR)

g

,

b

a

i

measure the extent

of preferred frame effects

(

a

i

= 0 -

i

=1,2,3 for GR)

z

i

and

a

3

measure the failure

of conservation of energy,

momentum and angular momentum

.

(

z

i

= 0 -

i

=1,2,3 for GR)Slide18

LLI: what are the implication?

Observer transformation invariance means laws of physics do not depend on the frame orientationParticle transformation is when the particle is moving with respect to a fixed reference frameIf there is a Lorentz violation, physical laws could be different for a moving observer vs. a stationary oneIt has been demonstrated that LLI violation implies CPT violation Slide19

Verifying LLI

The results of various experiments can be interpreted as a local verification the laws of Special Relativity (SR), for example when we checkthe role played by the Lorentz group in relativistic kinematics (the four-momentum conservation).the decay times of elementary particles- In vacuum the light does not travel at a constant speed c in all frames of reference, Regardless of the motion of the source and the observer - The laws of physics have not the same form in all inertial reference systemsConsequence of the SR violation

Extremely well verified in a context of Particle Physics Experiments Slide20

Verifying LLI

c is not any more constant c’ = c + k vthe space-time is not any more isotropicA violation of Lorentz invariance can be described by adding to the "dynamic invariant" additional vector or tensor fields ("background” fields), constant or slowly time-varying, which are coupled directly with the matter

k

< 2 10-9

Measuring the arrival time of pulses

from the binary X ray sourcesSlide21

Current experiments

Limits set from astronomical observationsMeasurements on light from GRB show that the speed of light does not vary with energy.Clock-Comparison ExperimentsStudy of the energy level of nucleons to find anisotropies in their frequenciesQED tests in Penning Traps(g-2) measurement in Electron-Positron and Proton-Antiproton (examined g= ws/wc ~ 2 , i.e. the anomaly wa =|ws-

wc| measured directly, 2.4 x 10-21

me , or for sidereal orientation under consideration of Earth's orientation, 1.6 x10

-21 me

) Muonium spectroscopy

search for deviations in the anomaly frequency of m – anti-

m, direct and for sidereal variations

University of Washington

Spin-polarized torsion pendulum

search for anisotropies with respect

to electron spins

(The octagonal pattern of magnets has an overall spin polarization in the octagon’s plane, defining preferred direction in the space. The whole apparatus is mounted on a turntable and when we turn the LI viol. determine a torque on the balance)Slide22

Verifying LPI

An historical test of GR: the Pound and Rebka experimentGlen Rebka at the lower end of the Jefferson Towers, Harvard UniversityConsequence of LPI violation is that

Gravitational Red-Shift ExperimentsSlide23

Recent LPI limits

(A. Bauch and S. Weyers: PHYSICAL REVIEW D, 65, 081101-R)(David Norris – Phys G -Spring 2007)Four NIST H masers ( Dn/n =2x10-16 1/day compared to Cs clock standards from NIST, Germany, France, and Italy over a period from 1999 to 2006. The variation of frequency correlated with changes in the gravitational potential due to the earth’s orbit was extracted: |a|< 1.4 x 10-6LPI violation implies the change of fundamental physical constants such as for example the fine structure constant.

Measurement of concentration ratio of Sm149 / Sm147 in the Oklo mine (a natural nuclear reactor in Gabon) compared to the expectation on the base of the assumption of the variation of the fission cross-section Slide24

Credit M. Giammarchi

–INFN Milano1S-2S v=2 466 061 413 187 103 (46) HzNatural width: 1.3 Hz

Results achieved on HydrogenD

n/n =

1.5 10-14

Cold beam PRL84 5496 (2000) M. Niering et al

Dn

/n =

10-12 Trapped H

PRL 77 255 (1996) C. Cesar et al

Requires antihydrogen at

mK temperature (laser cooling)

Experimental

CPT

tests



LI tests

D

n

/

n

=

10

-13

GS-HFS measured to 1 mHz:Slide25

Verifying UFF

The violation of UFF can be associated to the any kind of energy content of the sample Internal energy of the sample associate to the interaction

A

UFF

violation

factor associate

to the

interaction A

To evaluate the experimental results we introduce the EÖTVÖS ratio

For a weak violationSlide26

UFF and the nature of the mass

In the case of laboratory experiments the typical main energetic contribution is due to the strong nuclear interactionZ Atomic Number, A Mass Number

=1 ==>> A even, Z odd  = -1 ==>> A even, Z

even =0 ==>> A

odd

For example in the case Al - Pl

(

E

S

/ mc

2)

Pl - (E

S / mc2

)Al

»

2

x 10-3

|

h

S

|

<

5

10

-10

Slide27

The basic instrument of Experimental Gravitation

The torsion Balance 200 years of evolution:G measurementUFF testSearch of LI violationSlide28

Composition dependent experiments;

a couple of original examples1

F

g1

F

in1

F

g2

F

in2

2

g

sun

DICKE

:

torsional

pendulum

8-Body Torsion Pendulum used in the

Eöt

-Wash III Instrument

8-Body Torsion Pendulum used in the

Eöt

-Wash III Instrument

The

torsional

pendulum of

Loránd

von

Eötvös

Slide29

Composition Dependent - II

Free-Fall experimentSlide30

Credit M. Giammarchi

– INFN Milano10-1810-16WEP tests on matter system

10-14

10

-12

10

-10

10

-4

10-6

10-8

10

-2

1700

1900

1800

2000

No direct measurements on gravity effects on antimatter

“Low” precision measurement (1%) will be the first one

Can be done with a beam of Antiatoms flying to a detector!

AEGIS first phase

g

H

L

Composition dependent test –III

Gravity and anti-matterSlide31

1) Produce

ultracold antiprotons (100 mK)2) Accumulate e+3) Form Positronium (Ps) by e+ interaction with porous target4) Laser excite Ps to get Rydberg Ps

5) Form Rydberg cold (100 mK) antihydrogen by

6) Form a beam using an inhomogeneous electric field to accelerate the

Rydberg

antihydrogen7) The beam flies toward the

deflectometer which introduces a spatial modulation in the distribution of the Hbar

arriving on the detector8) Extract g from this modulated distribution

Cold antiprotons

e+

Porous target

Moire’ deflectometer and detector

AEGIS

strategy

Credit M.

Giammarchi

– INFN MilanoSlide32

Composition independent tests:

studying Gravity vs. distanceGeneral relativity (GR) predicts deviations from Newtonian gravity at the several-meter level in the lunar orbit. So millimeter-level measurement precision puts GR to a hard test and those can be obtained by the Lunar Laser Ranging (LLR). Limits on PPN b < 5 10-3

Apollo 15 retroreflector consisting of 300 corner-cube 3.8 cm set in hexagonal array. Apollo 11 mirror

Wenzel LLR station (Germany)

LLR @McDonald Observatory

• Ex. : (

mem)Brane

theory predicts Moon anomalous precession of ~ 1 mm/orbit, in addition to GR geodetic precession

• Now LLR accuracy few mm (thanks to APOLLO station). In the future by

MoonLIGHT 

100 μmSlide33

S

Orbit

equation

in

central

fiel

d

a

u

(

q

)

By

Iincluding

a the

perturbation

effect

due

to

a

Yukawa

potential

to

the

1

/r

2

law

,

we

get

a

perielium

precession

m

Limit

on

l

unar

orbit

precession

<

3

10

-11

for

l

~

10

8

m

Gravity at planetary distances Slide34

Gravity at interplanetary distances - ISlide35

Gravity at interplanetary distances - II

The Pioneer anomaly has been registered on two deep space probes with the best navigation accuracy: Pioneer 10 and 11.The effect is the observed deviation from predicted acceleration after they passe about 3 1012 m ( 20 A.U.) on their trajectories- The two probes are identical. The two trajectories are similar . No trajectory correction via thrusters The spacecrafts are spin stabilized

Launched in 1972 and 1973, the first hint of the effect is dated 1980 and the last contact in 2003 Newer spacecraft have used spin stabilization for some or all of their mission, including both Galileo and Ulysse

. These spacecraft indicate a similar effect, but too faint to be conclusif.

TSlide36

Gravity at interplanetary distances - III

ap=(8.73 + 1.33) 10-10 m/s2

Anderson et al Phys Rev. D 65 (2002) 082004

Doppler observable

f/f

o = 1 – 2v

P/c

vp

– v model

= - ap

(t- t

in)Slide37

Gravity at interplanetary distances - IV

ANDERSON et al. PHYS. REV. D 65 082004 (2002)The 2012 Explanation: thermal recoil forceThe spacecraft is powered by a radioisotope generator (RTG), which can emit heat in a preferred direction determining the opposite movement of the spacecraft.However, all thermal models predict a decrease in the effect with time, which did not appear in the initial analysis.A long effort was needed to recover old thermal data for showing the effective decrease with time

S.G. Turyshev et al. PRL 108, 241101 (2012)Slide38

Limits on PPN parametersSlide39

Gravity at short distance

For solving the hierarchy problem, i.e. the enormity of the difference between the electroweak scale mEW∼103 GeV and the Planck scale MPl=GN−1/2∼1018 GeV, it has been pointed out that one way is to probe the gravity law at distance well below 10 mm. While electroweak interactions have been probed at distances approaching ∼mEW−1, gravitational forces have not remotely been probed at distances ∼MPl−1.Our interpretation of MPl as a fundamental energy scale (where gravitational interactions become strong) is based on the assumption that gravity is unmodified over the 32 orders of magnitude between where it is measured at ∼ 10-3 mm down to the Planck length ∼10−35

m Moreover, small value of the cosmological constant  could be

stabilized by particles of wavelength ~ 0.1 mm (R. Sundrum, J. High Energy Phys,

9907, 001(1999))Slide40

Testing

gravity by means of gravimeters

Use

of

gravimeters

to

measure

the

modulation

of

the

gravity

due

to

the

change

of

the water

level

in

artificial

lakes

a

< 10

-3

for

l

~ 10

m

D

M

g

(

0

)

g

(

z

)

M -

D

M

D

M

Gravimeters in a mine

Gravimeters on a television tower

a

<

10

-4

for

l

~1 kmSlide41

Few classical tests

R.Spero et al., Phys.Rev.Lett. 44, 1645-1648 (1980)< 10-4 for

l from

2 to

5 cm

Fe

Cu

Fe

Cu



Astone

P. et al,

Eur. Phys. Jour. C

5, 651-664, (1998)



Slide42

Beyond

GR ?Slide43

Credit to

S. J. Smullin, Stanford University

25 µm

Gravity below 1 cm

Gold Test Mass

Au/Si Drive Mass

Piezo

Actuator

(+/-

120

µ

m

at

f

0

/3

)

Fiber for interferometer

Cover wafer

Cantilever

Shield wafer

(not shown in zoomed image)

Drive mass

Metallization

Figure Not to Scale

f

0

Andrew A.

Geraci

, Sylvia J.

Smullin

, David M. Weld, John

Chiaverini

, and

Aharon

Kapitulnik

, Phys. Rev. D 78, 022002 (2008)Slide44

Credit to

S. J. Smullin, Stanford UniversityGravity at short distance – II :the fiber interferometer

Laser

Diode

PD

PD

Signal

Reference

Fiber Coupler

Cryostat

Feed-through

Cantilever

Specifications



= 1310 nm

Cantilever end of fiber cleaved

Power striking cantilever ~10



W

Above 1kHz, noise floor ~0.01 Å/√Hz

May subtract/divide Reference

Fiber

Cantilever

Fabry-Perot CavitySlide45

Gravity at short distance III

The Stanford limits set measuring forces in the 10-18 N (atto) range.A long list of limiting noiseThermal noise of the cantileverInterferometer NoiseElectrostatic patchesMagnetic backgroundThen , they have to correct for a bias effect: the

Casimir forceSlide46

The

Casimir effect: the vacuum energy in an e.m. cavity

x

y

z

a

L

The

CASIMIR effect

In a total reflecting. cavity the permitted

e.m

. modes are the

k

z

=

n

p

/a

f

or any value of

k

x

e

k

y

G. Bressi, G. Carugno, R. Onofrio, G. Ruoso: Phys Rev Lett 88,

41804 (2002): primo sistema con piatti metallici

z

y

x

In the case of Stanford they computed the differential

Casimir

force between Au and Si of, allowing to set a limit at a force value 2 x10

-20

N, for

a

=1 and

l

= 20 mm.Slide47

Weighing the vacuum: the gravitational mass of the

e.m. vacuum Towards measuring the Archimedes force of vacuumE.Calloni, M.De Laurentis, R. De Rosa, F. Garufi, L. Rosa, L, Di Fiore,G. Esposito, C.Rovelli, P. Ruggi, F. TafuriarXiv:1401.6940Vacuum energy Gravitational Mass

Space-time curvature

?

The idea is to create a lack of vacuum energy in a volume :

- if

- the vacuum energy gravitates

-then

-this volume floats in the sea of virtual photons around us

Measuring the Archimede force of the Vacuum Slide48

Measuring the Archimedes force of vacuum

Cavity plates transparent  the weight of virtual photons is higherCavity plates reflective  virtual photons will be expelled and the weight decreases.The proposed technique; - take advantage of the high Tc superconducting transition of special mirrors ( from semi- to super- conductors)The floating force per unit surface is extremely tiny, so that we need to modulate the vacuum energy contained in the cavitySlide49

Measuring weak forces

Measuring the effect by modulating at low frequency and exciting the a torsion pendulum at the resonanceMeasuring the effect by using Advanced VIRGO with Tobs= 6 month Slide50

Archimede

and GW detectorsSketch of the optical link. GW-EM: Gravitational wave detector's test masses; AF-IM(EM): Archimedes Force apparatus input(end) mirror; GW-beam: laser beam of the gravitational wave detector. The AF cavity length is 12 meters, compatible with the present Virgo halls.Slide51

Summary of the limits at short distancesSlide52

Summary

of the limits up to 1014 mSlide53

Conclusion

Measurement of fine effects in experimental physics, especially in gravitational experiments, needs high technology and nontrivial methods. New experiments, which are now in progress thanks to the technological development in the various world gravitational centers, will be a successive stage in the knowledge of the nature of the gravitational interaction.Our wish is that the new gravitational laboratory at the department of Physics of the FEDERICO II university can give crucial contributions to unification scenario of all the fundamental interactionsSlide54

Extra slidesSlide55

The hierarchy problem

A hierarchy problem occurs when the fundamental parameters, such as coupling constants or masses are vastly different than the parameters measured by experiment. This can happen because measured parameters are related to the fundamental parameters by a prescription known as renormalization. Hierarchy problems are related to fine-tuning problems. In some cases, it appears that there has been a delicate cancellation between the fundamental quantity and the quantum corrections.Studying the renormalization in hierarchy problems is difficult, because such quantum corrections are usually power-law divergent, which means that the shortest-distance physics are most important.Researchers postulate new physical phenomena that resolve hierarchy problems without fine tuning.