Astrophysical and cosmological aspects of feebly-interacting light species
Josef Pradler Austrian Academy of Sciences
PIRSA:14060027
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Inflationary Gravitational Waves: Recent Developments and Next Steps
Marc Kamionkowski Johns Hopkins University - Department of Physics & Astronomy
PIRSA:14060024 -
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New methods for detecting short-range forces and gravitational waves using resonant sensors
Andrew Geraci University of Nevada Reno
PIRSA:14060019 -
The Exact Renormalization Group and Higher Spin Holography.
Rob Leigh University of Illinois Urbana-Champaign
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Probing Gravity and Small Forces with Torsion Balances
Blayne Heckel University of Washington
PIRSA:14060018 -
Resonant Detection of Short-Range Gravitational Forces
Eli Levenson-Falk University of Southern California
PIRSA:14060046 -
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Astrophysical and cosmological aspects of feebly-interacting light species
Josef Pradler Austrian Academy of Sciences
PIRSA:14060027More 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. -
Cosmological Constraints on Ultra-light Axions
David Marsh King's College London
PIRSA:14060026Ultra-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. -
Axions: Past, Present and Future
Surjeet Rajendran Stanford University
PIRSA:14060025I 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. -
Inflationary Gravitational Waves: Recent Developments and Next Steps
Marc Kamionkowski Johns Hopkins University - Department of Physics & Astronomy
PIRSA:14060024The 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. -
Precision Spectroscopy of Atomic Lithium
Jason Stalnaker Oberlin College
PIRSA:14060022The 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. -
A quantum network of clocks
Mikhail Lukin Harvard University
PIRSA:14060021By 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. -
Dark Energy and Testing Gravity
Raman Sundrum University of Maryland, College Park
PIRSA:14060020I 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. -
New methods for detecting short-range forces and gravitational waves using resonant sensors
Andrew Geraci University of Nevada Reno
PIRSA:14060019High-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). -
The Exact Renormalization Group and Higher Spin Holography.
Rob Leigh University of Illinois Urbana-Champaign
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Probing Gravity and Small Forces with Torsion Balances
Blayne Heckel University of Washington
PIRSA:14060018The 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.
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Resonant Detection of Short-Range Gravitational Forces
Eli Levenson-Falk University of Southern California
PIRSA:14060046Some 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. -
f(R) Gravity and Cosmology
Valerio Faraoni Bishop's University
PIRSA:14060045A 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.