Sommerfeld Theory Colloquium (ASC)

Sommerfeld Theory Colloquium, Einstein is well known for his rejection of quantum mechanics in the form it emerged from the work of Heisenberg, Born and Schrodinger in 1926. Much less appreciated are the many seminal contributions

he made to quantum theory prior to his �final scientifi�c verdict, that

the theory was at best incomplete. In this talk I present an overview

of Einsteins many conceptual breakthroughs and place them in historical context. I argue that Einstein, much more than Planck, introduced the concept of quantization of energy in atomic mechanics.

Einstein proposed the photon, the fi�rst force-carrying particle discovered for a fundamental interaction, and put forward the notion of wave-particle duality, based on sound statistical arguments 14 years before De Broglies work. He was the fi�rst to recognize the intrinsic

randomness in atomic processes, and introduced the notion of transition probabilities, embodied in the A and B coeffi�cients for atomic emission and absorption. He also preceded Born in suggesting the interpretation of wave fi�elds as probability densities for particles, photons, in the case of the electromagnetic �field. Finally, stimulated by

Bose, he introduced the notion of indistinguishable particles in the

quantum sense and derived the condensed phase of bosons, which is

one of the fundamental states of matter at low temperatures. His

work on quantum statistics in turn directly stimulated Schrodinger

towards his discovery of the wave equation of quantum mechanics. It

was only due to his rejection of the �final theory that he is not generally recognized as the most central �figure in this historic achievement

of human civilization.

Sommerfeld Theory Colloquium, Since the emergence of information theory in the middle of the 20th century, this new scientific field has been deeply entangled with statistical physics, as attested from the beginning by the use of entropy to quantify information content. The talk will explore the major

impact of these transdisciplinary exchanges, with a particular focus on the important new research topic called "compressed sensing". Starting from the observation that interesting signals can be

compressed, and thus are sparse in some representation, compressed sensing aims at acquiring data directly in a compressed way, using

then computational methods to reconstruct the original signal. It

opens the way to faster, less destructive, and more e�ective signal acquisition, with possible applications in many branches of science,

from magnetic resonance imaging to astronomy, tomography, or gene

interaction network reconstruction. The talk will describe the spectacular progress that can be made using various statistical physics

ideas, from spin glass theory to crystal nucleation.

Sommerfeld Theory Colloquium, With the discovery of the Higgs boson and the determination of its mass, the Standard Model is complete and its parameters are now

known and over-constrained. I will review the status and future directions in precision electroweak physics both at high and low en- ergies. There is strong evidence that the Standard Model is correct at the level of quantum corrections, and that in the absence of major conspiracies, any new physics beyond it is either significantly heavier than the electroweak scale or very weakly coupled.

Sommerfeld Theory Colloquium, In this seminar, I shall describe recent work by our group on iden- tifying pockets of gas at high redshift that have undergone mini- mum processing through stars. The chemical composition of such gas still bears the imprints of the first few generations of stars that formed only a few hundred million years after the Big Bang, and thereby gives us clues to the physical properties of these still mys- terious objects which heralded the so-called ‘epoch of reionisation’. Near-pristine gas at high redshift is also the astrophysical environ- ment where the primordial abundance of deuterium can be measured most precisely. I will show how determinations of the cosmic den- sity of baryons from Big-Bang Nucleosynthesis and from the Cosmic Microwave Background have now reached comparable precision, in both cases of order of a few percent. The excellent agreement be- tween these two measures at widely different cosmic epochs places interesting limits on the existence of relativistic particles beyond the standard model of physics.

Sommerfeld Theory Colloquium, Remarkably, a strong candidate for Dark Matter exists within the Standard Model. Theoretical arguments suggest that QCD forces in the flavor-singlet sector may be strong enough that the H-dibaryon is a deeply-bound, compact state which is absolutely stable with a mass < 2mp. This possibility has gotten recent support from lattice QCD studies, which – although not yet at high enough resolution and sensitivity to confront the hypothesis – show a deeper binding than other states. As I will show, reasonable assumptions about the H’s mass and wave function lead to the observed dark matter density and DM-to- (3-quark) baryon ratio. I will discuss why H-DM is not excluded by the various experimental and observational limits, and discuss what its observational signatures would be.

Sommerfeld Theory Colloquium, I will describe the process of how to award Nobel Prizes and then give the history behind this year’s prize.

Sommerfeld Theory Colloquium, The problem of understanding how gravity fits together with other fundamental interactions of matter has been at the forefront of the- oretical research for many decades, leading to the rich framework of string theory and M-theory. In this framework, many fundamen- tal questions are being resolved, but many remain quite mysterious, suggesting that search for novel concepts may be well justified. I review the recent concept of multicritical gravity with Lifshitz-type anisotropic scaling, and its applications in areas ranging from par- ticle phenomenology beyond the standard model to non-relativistic

versions of the holographic AdS/CFT correspondence.

Sommerfeld Theory Colloquium, Absolute temperature, that is the fundamental temperature scale in thermodynamics, is usually bound to be positive. Under special con- ditions, however, negative temperatures - where high-energy states are more occupied than low-energy states - are also possible. In this talk, I will present a negative temperature state for motional degrees of freedom: By tailoring the Bose-Hubbard Hamiltonian we exper- imentally created an attractively interacting ensemble of ultracold bosons, which is stable against collapse for arbitrary atom numbers. In this negative temperature state, the quasi-momentum distribu- tion develops sharp peaks at the upper band edge, revealing thermal equilibrium and bosonic coherence over several lattice sites. Nega- tive temperatures imply negative pressures and open up new param- eter regimes for cold atoms, enabling fundamentally new many-body states and counterintuitive effects such as Carnot engines above unity efficiency. In addition, this system enabled us to study the dynam- ics of the phase transition from Mott insulator to superfluid and to experimentally investigate how fast phase coherence can spread.

Sommerfeld Theory Colloquium

Sommerfeld Theory Colloquium