**Geoff Blewitt**, University of Nevada

*Atomic Clocks Monitored to 0.2 ns using Satellite Geodesy*

Satellite geodesy uses the timing of photons from satellites to determine the Earth’s time varying shape, gravity field, and orientation in space, with accuracies of <1 part per billion, or millimeters at the Earth’s surface, and centimeters at satellite altitude. Implicit in mm-level GPS positioning is the modeling of widely separated atomic clocks with sub-ns precision. The precise monitoring of the relative timing phases between widely separated atomic clocks forms the metrological basis of a recently proposed approach to detect topological dark matter of a type that affects fundamental constants. Relative clock time can be updated as often as every second using the current global network of geodetic GPS stations that record data at that rate, though many more geodetic GPS stations record data every 30 seconds. Thus GPS could be used as the world’s largest dark matter detector, potentially sensitive to dark matter structures sweeping through the entire system >100 seconds, corresponding to speeds <500 km s¬-1 relative to the solar system. Here it is shown that relative timing phases can be determined to ~0.2 ns between the global network of atomic clocks at many geodetic GPS stations on the Earth’s surface separated as far as ~12,000 km, plus those aboard the 30 GPS satellites separated as far as ~50,000 km. Available atomic clock types include caesium (Cs), rubidium (Rb), and (on the ground) hydrogen maser (Hm). Achieving sub-ns relative timing precision requires (1) dual-frequency carrier phase data measured at the few mm level, (2) rigorous modeling of many aspects of the Earth system and GPS satellite dynamics, and (3) stochastic estimation of biases in the system. For example, solar radiation pressure from momentum exchange with photons hitting the satellites perturbs orbits at the few-meter level. Imperfect modeling, such as knowledge of the satellite attitude, requires us to estimate orbit acceleration biases as they slowly vary in time. For mm-level positioning applications, clock phases are considered to be unknown biases to be estimated as a white noise process, that is, estimated independently at every data epoch without constraint. By virtue of the common view of satellites simultaneously by multiple ground stations, relative clock time can be determined between all clocks in the entire satellite-ground system by estimating all biases in a global inversion. Since the timing phase between Hm clocks can be accurately extrapolated forward in time, they set the standard by which upper limits can be set on the precision of timing at any specific instant. As a feasibility study, a custom analysis of original raw GPS phase data was designed using the GIPSY OASIS II software (from NASA JPL), processing data from ~40 ground stations of various atomic clock type. An analysis of data from GPS stations that are positioned at the few-millimeter level every day indicates that Hm clock time is determined at to ~0.2 ns. Since the smoothness of Hm clocks is not assumed anywhere in the modeling, and that station clock type has no influence on positioning precision, one can infer that timing at the 0.2 ns level is also the case for less predictable atomic clocks such as Rb and Cs, thus providing a window into possibly different coupling of dark matter with different clock types.

**Kfir Blum**, Institute for Advanced Study

*Comments on the Chiral Lagrangian in an Axion-Like Background*

Axion dark matter that couples to the QCD instanton generates a series of non-renormalizable operators in the chiral Lagrangian. The coefficients of these operators are related through chiral perturbation theory. I discuss the implications of these relations for the spectrum and interactions of the axion, allowing for arbitrary mixing between multiple axion states in the UV. I derive constraints on the relation between the strength of an axion-induced oscillating nucleon EDM and the frequency of the oscillations.

**Robin Cote**, University of Conneticut

*Probing the electron-proton mass ratio variation with AMO systems*

**Andrei Derevianko,** University of Nevada

*Zen and the art of atomic time-keeping (Tutorial on atomic clocks for particle theorists)*

**Vladimir Dzuba**, University of New South Wales

*Search for new physics in atoms: cosmic PNC and variation of alpha.*

We consider pseudo-scalar and pseudo-vector interaction of atomic electrons with hypothetical dark matter particles (e.g., axions). These interactions lead to oscillating atomic parity non-conserving (PNC) amplitudes and/or oscillating electric dipole moments (EDM). In static limit for PNC, existing atomic PNC experiments can be used to constrain time component of the pseudo-vector field.

Possible variation of fundamental constants is suggested by theories unifying gravity with other interactions. Evidence of the space/time variation of the fine structure constant alpha is found in the quasar absorption spectra. Optical transitions in highly charged ions can be used as sensitive tools for studying time variation of alpha in laboratory.

**Valerio Faraoni**, Bishop's University

*f(R) Gravity and Cosmology*

A popular alternative to dark energy in explaining the current acceleration of the universe discovered with type Ia supernovae is modifying gravity at cosmological scales. But this is risky: even when everything is well for cosmology, other fundamental and experimental aspects of gravity must be checked in order for the theory to be viable. The successes of modified gravity and its challenges, which have generated a large body of literature in the past ten years, will be reviewed.

**Andrew Geraci**, University of Nevada

*New methods for detecting short-range forces and gravitational waves using resonant sensors *

New methods for detecting short-range forces and gravitational waves using resonant sensors High-Q resonant sensors enable ultra-sensitive force and field detection. In this talk I will describe three applications of these sensors in searches for new physics. First I will discuss our experiment which uses laser-cooled optically trapped silica microspheres to search for violations of the gravitational inverse square law at micron distances [1]. I will explain how similar sensors could be used for gravitational wave detection at high frequencies [2]. Finally I will describe a new method for detecting short-range spin-dependent forces from axion-like particles based on nuclear magnetic resonance in hyperpolarized Helium-3. The method can potentially improve previous experimental bounds by several orders of magnitude and can probe deep into the theoretically interesting regime for the QCD axion [3].

[1] A.Geraci, S. Papp, and J. Kitching, Phys. Rev. Lett. 105, 101101 (2010), [2] A. Arvanitaki and A. Geraci, Phys. Rev. Lett. 110, 071105 (2013), [3] A. Arvanitaki and A. Geraci, arxiv: 1403.1290 (2014).

**Blayne Heckel**, Washington University

*Probing Gravity and Small Forces with Torsion Balances*

The EotWash group at the University of Washington has developed a set of torsion balance instruments to probe the properties of gravity and to search for new weak forces. Current efforts focus on improved tests of the principle of equivalence, the inverse square law at short distances, and spin-coupled interactions. These experiments and prospects for the future will be discussed.

**Jason Hogan**, Stanford University

*Fundamental physics with atom interferometry*

Precision atom interferometry is poised to become a powerful tool for discovery in fundamental physics. Towards this end, I will describe recent, record-breaking atom interferometry experiments performed in a 10 meter drop tower that demonstrate long-lived quantum superposition states with macroscopic spatial separations. The potential of this type of sensor is only beginning to be realized, and the ongoing march toward higher sensitivity will enable a diverse science impact, including new limits on the equivalence principle, probes of quantum mechanics, and detection of gravitational waves. Gravitational wave astronomy is particularly compelling since it opens up a new window into the universe, collecting information about astrophysical systems and cosmology that is difficult or impossible to acquire by other methods. Atom interferometric gravitational wave detection offers a number of advantages over traditional approaches, including simplified detector geometries, access to conventionally inaccessible frequency ranges, and substantially reduced antenna baselines.

**Marc Kamionkowski**, Johns Hopkins University

*Inflationary Gravitational Waves: Recent Developments and Next Steps*

The recently reported evidence for the cosmic microwave background signature of inflationary gravitational waves is very tantalizing. I will discuss how the measurement is done, the evidence presented by BICEP2, the interpretation, and some of the criticisms of the arguments presented by BICEP2 that the signal is not dust-dominated. I will then review next steps to be taken with future CMB experiments and with galaxy surveys.

**Hidetoshi Katori**, RIKEN

*Frequency comparison of cryogenic optical lattice clocks*

We report frequency comparison of two Sr optical lattice clocks operated at cryogenic temperature to dramatically reduce blackbody radiation shift. After 11 measurements performed over a month, the two cryo-clocks agree to within (-1.1±1.6)×〖10〗^(-18).

Current status of a frequency ratio measurement of Hg/Sr clocks and a remote comparison of cryo-clocks located at Riken and University of Tokyo will be mentioned.

**Mikhail Kozlov**, Petersburg Nuclear Physic Institute

*Spectroscopic constrains on variation of fundamental constants in astrophysics.*

I will discuss present limits on the variation of the fine structure constant and the electron to proton mass ratio from the astrophysical data on the spectra from the interstellar gas medium.

The emphasis will be made on the infrared and microwave spectra. Such spectra may be 2 - 3 orders of magnitude more sensitive to the variation of constants than optical spectra.

**Nathan Leefer**, University of California, Berkeley, Helmholtz Institute Mainz &

**Szymon Pustelny**, Uniwersytet Jagiellonski

*Optical magnetometry - From basics to Global Network of Optical Magnetometer for Exotic physics*

In our talk we seek to present a broad overview of the field of optical magnetometers, starting from basic principles to fundamental limitations to the variety of applications in which they have already found use. We will end with a report on the development of a new worldwide network of synchronized magnetometers that can be used to search for a variety of new physical phenomena (many of which are discussed at this conference!).

**Eli Levenson-Falk**, Stanford University

*Resonant Detection of Short-Range Gravitational Forces*

Some theories predict a short-range component to the gravitational force, typically modeled as a Yukawa modification of the gravitational potential. This force is usually detected by measuring the motion of a mechanical oscillator driven by an external mass. In this talk I will discuss such an apparatus optimized for use in the 10-100 micron distance range. The setup consists of a cantilever-style silicon nitride oscillator suspended above a rotating drive mass. Periodic density variations in the drive mass cause an oscillatory gravitational force on the cantilever, whose position is read out using optical interferometry. In order to drive the cantilever precisely on resonance, it must have a broad resonant peak; however, lower quality factors reduce force sensitivity by reducing the amplitude of oscillation for a given drive force. We solve this problem by implementing an effective damping on the oscillator by use of optical feedback. I will discuss further applications of this feedback technique, as well as improvements to the apparatus and future experiments.

**Mikhail Lukin**, Harvard University

*A quantum network of clocks*

By combining precision metrology and quantum networks, we describe a quantum, cooperative protocol for the operation of a network consisting of geographically remote optical atomic clocks. Using non-local entangled states, we demonstrate an optimal utilization of the global network resources, and show that such a network can be operated near the fundamental limit set by quantum theory yielding an ultra-precise clock signal. Besides serving as a real-time clock for the international time scale, the proposed quantum network also represents a large-scale quantum sensor that can be used to probe the fundamen- tal laws of physics, including relativity and connections between space-time and quantum physics. Prospects for realization of such networks will be discussed.

**Jeremy Mardon**, Stanford University

*Ultra-light hidden photons*

**David Marsh**, Perimeter Institute

*Cosmological Constraints on Ultra-light Axions*

Ultra-light axions (ULAs) with masses in the range 1e-33 eV< m < 1e-18 eV can constitute a novel component of the dark matter, which can be constrained by cosmological observations. ULA dark matter (DM) is produced non-thermally via vacuum realignment in the early universe and is cold. Pressure perturbations, however, manifest a scale in the clustering (also the de Broglie scale). For the range of masses considered this spans the Hubble scale down to sub-galactic scales. In the model-independent adiabatic mode of initial conditions, one can gain strong constraints on ULAs as DM from the CMB and large scale structure (LSS). I will present constraints from Planck and WiggleZ, constraining m~1e-33 eV to 1e-25 eV at the percent level. In the range m\gtrsim 1e-22 eV ULAs may also solve the "small-scale problems" of CDM, and suggest other constraints from LSS and high-z observations, constraining m\lesssim 1e-22 eV to be sub-dominant in DM. Future prospects from CMB lensing, and from Euclid galaxy weak lensing, will make sub-percent constraints out to m~1e-21 eV. Model-dependent couplings between axions and photons provide still other bounds from CMB spectral distortions. Finally, if the inflationary energy scale is high, corresponding to an observable tensor-to-scalar ratio, then CMB isocurvature perturbations provide the strongest constraints on m>1e-24 eV, ruling out ULA dark matter in the simplest inflationary scenarios over the entire range considered, as well as the "anthropic window" for the QCD axion.

**Ekkehard Peik**, Physikalisch-Technische Bundesanstalt

*Atomic Clocks and Tests of Fundamental Physics*

The precision of atomic clocks continues to improve at a rapid pace: While caesium clocks now reach relative systematic uncertainties of a few 10-16, several optical clocks based on different atomic systems are now reported with uncertainties in the 10-18 range. This variety of precise clocks will allow for improved tests of fundamental physics, especially quantitative tests of relativity and searches for variations of constants. Laser-cooled and trapped ions permit the study of strongly forbidden transitions with extremely small natural linewidths and long coherence times. The frequency of the electric octupole transition S1/2 - F7/2 at 467 nm in 171Yb+ with a natural linewidth in the nHz range is remarkably insensitive against external electric and magnetic fields. We evaluate the systematic uncertainty of a frequency standard that is based on this transition as 4*10-18 at present. An even better isolation from external perturbations can be expected for the nuclear transition in 229Th3+ at about 160 nm with an expected linewidth in the mHz range. In order to excite the so far only indirectly observed nuclear transition using electronic bridge processes, we investigate the dense electronic level structure of Th+. Both transitions, in Yb+ and 229Th, are predicted to be highly sensitive to changes in the fine structure constant. I will give an update on limits on variations of constants as obtained from atomic clock comparisons.

**Josef Pradler**, Johns Hopkins University

*Astrophysical and cosmological aspects of feebly-interacting light species*

More often than not, astrophysical probes are superior to direct laboratory tests when considering light, very weekly interacting particles and it takes clever strategies and/or ultra-pure experimental setups for direct tests to be competitive. In this talk, I will review the astrophysical side of the story with a particular focus on dark photons and axion-like particles. I will also present some recent results on the emission process of dark photons with mass below 10 keV from the interior of stars. Compared to previous analyses, limits on dark photons are significantly improved, to the extent that many dedicated experimental searches find themselves inside astrophysically excluded regions. However, constraints on the atomic ionization rate from a solar flux imposed by Dark Matter experiments offer a new test of such states, surpassing even the most stringent astrophysical limits. The model also serves as a prototype scenario for energy injection in the early Universe and I will show how cosmology offers unique sensitivity when laboratory probes are out of reach. Time permitting, I may also briefly comment on very light axions and their cosmology.

**Surjeet Rajendran**, Stanford University

*Axions: Past, Present and Future*

I will review the theoretical motivations for axion and axion-like-particles. I will then discuss bounds on such particles and highlight ways to experimentally probe them.

**Michael Romalis**, Princeton University

*Atomic magnetometers for precision measurements*

Atomic magnetometers have a long history in tests of Standard Model since they provide sensitive constraints on new spin interactions. I will review recent progress in magnetometry using electron and nuclear spins, describe some of the limits set on new physics and discuss ideas for future experiments.

**Jeffrey Sherman**, National Institute of Standards and Technology

*Time and frequency metrology at NIST*

Official U.S. time is currently realized by an ensemble of commercial cesium-beam atomic clocks and hydrogen masers. Cesium-fountain devices presently serve as ultimate frequency references and help to define the SI second. The present quandary is: these microwave-based standards are rapidly becoming outmatched by new optical atomic frequency references---by a factor of 1,000 in stability, and perhaps a factor of 100 in accuracy. I will survey the ongoing optical atomic clock projects at NIST and highlight related work in optical time and frequency measurement and transfer.

**Yevgeny Stadnik**, University of New South Wales

*Axion-induced effects and topological defect dark matter detection schemes*

We discuss new observable effects of axionic dark matter in atoms, molecules and nuclei. We show that the interaction of an axion field, or in general a pseudoscalar field, with the axial-vector current generated by an electron through a derivative-type coupling can give rise to a time-dependent mixing of opposite-parity states in atomic and molecular systems. Likewise, the analogous interaction of an axion field with the axial-vector current generated by a nucleon can give rise to time-dependent mixing of opposite-parity states in nuclear systems. This mixing can induce oscillating electric dipole moments, oscillating parity nonconservation effects and oscillating anapole moments in such systems. By adjusting the energy separation between the opposite-parity states of interest to match the axion mass energy, axion-induced experimental observables can be enhanced by many orders of magnitude. Oscillating atomic electric dipole moments can also be generated by axions through hadronic mechanisms, namely the P,T-violating nucleon-nucleon interaction and through the axion-induced electric dipole moments of valence nucleons, which comprise the nuclei. The axion field is modified by Earth’s gravitational field. The interaction of the spin of either an electron or nucleon with this modified axion field leads to axion-induced observable effects. These effects, which are of the form g • σ, differ from the axion-wind effect, which has the form pa • σ.

We also propose schemes for the detection of topological defect dark matter using pulsars and other luminous extraterrestrial systems via non-gravitational signatures. The dark matter field, which makes up a defect, may interact with standard model particles, including quarks and the photon, resulting in the alteration of their masses. When a topological defect passes through a pulsar, its mass, radius and internal structure may be altered, resulting in a pulsar `quake'. A topological defect may also function as a cosmic dielectric material with a frequency-dependent index of refraction, which would give rise to the time delay of a periodic extraterrestrial light or radio signal, and the dispersion of a light or radio source in a similar manner to an optical lens. The biggest advantage of such astrophysical observations over recently proposed terrestrial detection methods is the much higher probability of a defect been found in the vast volumes of outer space compared with one passing through Earth itself.

References:

(1) Phys. Rev. D 89, 043522 (2014).

(2) arXiv:1404.2723.

(3) arXiv:1405.5337.

**Jason Stalnaker**, Oberlin

*Precision Spectroscopy of Atomic Lithium *

The simplicity of the atomic structure of lithium has long made it a system of theoretical interest. With the development of stabilized optical frequency combs, it is possible to achieve experimental accuracies that provide significant tests of atomic theory calculations as well as a window into nuclear structure. I will discuss an ongoing experimental effort at Oberlin College to measure the energy levels of lithium using a stabilized optical frequency comb.

**Raman Sundrum**, University of Maryland

*Dark Energy and Testing Gravity*

I will review why the mild acceleration of the Universe poses a major puzzle, the Cosmological Constant Problem, for the connection between gravity and matter, suggesting a possible breakdown in the standard general relativistic and field theoretic description. Thus far theorists have failed to provide any very concrete and testable resolution. I will however discuss some simple theoretical ideas that suggest directions for experiments to lead the way.

**Guglielmo Tino**, Istituto Nationale di Fisicia Nucleare

*Precision gravity measurements with cold atom interferometry*

I will discuss experiments we are conducting for precision tests of gravitational physics using cold atom interferometry. In particular, I will report on the measurement of the gravitational constant G with a Rb Raman interferometer, and on experiments based on Bloch oscillations of Sr atoms confined in an optical lattice for gravity measurements at small spatial scales and for testing Einstein equivalence principle.

**Lutz Trahms**, Physikalisch-Technische Bundesanstalt

*Nuclear spin precession of noble gases in ultra low magnetic fields*

In the low energy re¬gime, precision measurements of spin precession have gained increased attention as an alternative pathway to physics beyond the standard model. These measurements aim at the detection of minute frequency changes superimposed on low Larmor frequencies at extremely weak magnetic fields. Such measurements require an effective shielding against the magnetic field of the Earth and other perturbations. For measuring the precession frequency with high precision, a long lifetime of the precessing nuclear magnetization is required, thus the homogeneity of the applied field is a crucial parameter. In addition, criteria are needed that unambiguously distinguish magnetic artifacts from the non-magnetic exotic interactions that we search for. This can be accomplished by the concept of co-magnetometry, i.e., by simultaneous measuring the precession of two nuclear species such as 3He and 129Xe. Yet another kind of co-magnetometry is the use of SQUIDs for monitoring the spin precession. SQUIDs are magnetic field detectors of their own kind, which can measure the oscillating magnetic field generated by the precessing nuclear magnetic moment as well as the magnetic dc background field. In this presentation, I will report on the current state of the art in our lab in measurements of nuclear spin precession of noble gases.