Astrophysics and Cosmology
The largest objects: galaxy clusters
Uri Keshet
The Perseus cluster core (Chandra) with highlighted spiral cold fronts and X-ray cavities.
Galaxy clusters, as the largest virialized objects ever to form in the Universe, link cosmology and astrophysics. These 'island-universe' objects are mainly composed of dark matter and a hot, dilute plasma. Their stability is an open question, as the strong X-ray emission should have naively led to catastrophic cooling and collapse. Over the past decade, mysterious spiral structures were found in practically all clusters. They may be driven by the giant black hole lurking in the center of every cluster, for example through the relativistically hot bubbles it injects into the plasma (figure).
Condensed Matter Theory
Nonequillibrium dynamics
Yevgeny Bar Lev
Spreading of density excitation in a two-dimensional Fermi-Hubbard model
While conventionally condendsed matter theory was moslty concerned with equilibrium or stationary states situations, recent theoretical and experimental progress spurred interest in nonequillibrium. In our group we study various situations of nonequillibrium dynamics, such as transport, quenches and external driving.
High-Energy Physics
Cosmology
Ram Brustein
A new class of cosmic inflation models
The early universe is used as a theoretical laboratory for studying fundamental physics, the laws of gravity and quantum mechanical aspects of matter under extreme conditions. We study models of cosmic inflation in the early universe and dark energy in the late universe and their possible realizations in quantum field theory and string theory models. Our recent research focuses on models of high-scale inflation which produce an observable signal of gravitational waves in the cosmic microwave background.
Biological and Soft Matter Physics
Dynamics of Complex Fluids and Geophysical Flows
Roiy Sayag
Experiment of polymer solution flowing radially under weak friction
The front of a fluid that displaces a less viscous fluid in shear-dominated flows is known to be stable. We show that in predominantly extensional flows on a sphere, a similar front of a strain-rate-softening fluid can become unstable and evolve fingerlike patterns comprised of rifts and tongues. The number of rifts and tongues declines with time and is selected by competition between interfacial hoop stress, geometric stretching, momentum dissipation, and spatial curvature. Our results elucidate fracture dynamics in complex fluids under extension and are applicable to a wide range of systems, including planetary-scale ice shelves as in snowball epochs and icy moons.
Condensed Matter Experimental
Noise in strongly correlated systems
Grzegorz Jung
Normalized spectral density and R(T) for distinct resistivity states
To many physicist the subject of fluctuations appears esoteric and even pointless; spontaneous fluctuations seem nothing but an unwanted evil which only an unwise experimenter would encounter. In reality, noise enables a deep insight into physics of the system. Recently, we have employed noise to discriminate various resistivity states in the ferromagnetic insulating manganite La0.86Ca0.14MnO3. Different states arise due to transitions between local minima of the electronic glass potential landscape. Remarkably, freezing into the glass state is marked by the onset of non-Gaussian noise.
Atomic, Molecular and Optical Physics
Quantum Interferences and Lasing without inversion
Reuben Shuker
Sub-natural-width peak
Quantum-interference-related phenomena have many implications in physics. Quantum interference between two independent quantum channels in three-level systems gives rise to various coherent phenomena, such as electromagnetically induced transparency (EIT), coherent population trapping (CPT), lasing/gain without inversion (LWI/GWI), enhancement of refraction index, sub- and super-luminal light propagation etc. These phenomena open a wide-range perspective for new type of phase-sensitive spectroscopy. An example is the possibility to get sub-natural line widths (see movie).