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Events on Friday, February 28th, 2014

Theory Seminar (High Energy/Cosmology)
Pure Gravity Mediation
Time: 2:00 pm
Place: 5280 Chamberlin Hall
Speaker: Jason Evans, University of Minnesota
Abstract: If low energy supersymmetry is realized in nature, the apparent discovery of a Higgs boson with mass around 125 GeV suggests a supersymmetric mass spectrum in the TeV or multi-TeV range. Multi-TeV scalar masses are a necessary component of supersymmetric models with pure gravity mediation or in any model with strong moduli stabilization. The simplest model of pure gravity mediation contains only two free parameters: the gravitino mass and $tan beta$. Scalar masses are universal at some high energy renormalization scale and gaugino masses are determined through anomalies and depend on the gravitino mass and the gauge couplings. This theory requires a relatively large graviton mass (m_{3/2} gtrsim 300 TeV) and a limited range in tan beta simeq 1.7--2.5. By allowing for non-unversalities in the Higgs soft masses, the allowed range in tan beta is greatly increased which then permits smallers values of m_{3/2} and makes detection of the gluino at the LHC possible. Furthermore, if one adopts a no-scale or partial no-scale structure for the K"ahler manifold, sfermion masses may vanish at the tree level. It is usually assumed that the leading order anomaly mediated contribution to scalar masses appears at 2-loops. However, there are at least two possible sources for 1-loop scalar masses. These may arise if Pauli-Villars fields are introduced as messengers of supersymmetry breaking. We consider the consequences of a spectrum in which the scalar masses associated with the third generation are heavy (order $m_{3/2}$) with 1-loop scalar masses for the first two generations. A similar spectrum is expected to arise in GUT models based on $E_7/SO(10)$ where the first two generations of scalars act as pseudo-Nambu-Goldstone bosons. Explicit breaking of this symmetry by the gauge couplings then generates one-loop masses for the first two generations. In particular, we show that it may be possible to reconcile the $g_mu - 2$ discrepancy with potentially observable scalars and gauginos at the LHC.
Host: Jordi Salvadó Serra
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Physics Department Colloquium
A single Rydberg electron in a Bose-Einstein Condensate
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Prof. Tilman Pfau, University of Stuttgart
Abstract: Electrons attract polarizable atoms via a 1/r^4 potential. For slow electrons the scattering from that potential is purely s-wave and can be described by a Fermi pseudopotential. To study this interaction Rydberg electrons are well suited as they are slow and trapped by the charged nucleus. In the environment of a high pressure discharge Amaldi and Segre, already in 1934 observed a lineshift proportional to the scattering length [1], which was first introduced to explain their findings.
At ultracold temperatures and Rydberg states with medium size principle quantum numbers n, one or two ground state atoms can be trapped in the meanfield potential created by the Rydberg electron, leading to so called ultra-long range Rydberg molecules [2]. These molecules can show a linear Stark effect corresponding to a permanent dipole moment [3], which if seen from a standpoint of traditional molecular physics is surprising.
At higher Rydberg states the spatial extent of the Rydberg electron orbit is increasing. For principal quantum numbers n in the range of 100-200 and typical BEC densities, up to several ten thousand ground state atoms are located inside one Rydberg atom, leading again to a density dependent energy shift of the Rydberg state. This allows, together with the strong van-der-Waals blockade, to excite only one single Rydberg atom in a condensate. We excite a Rydberg electron with n upto 202 in the BEC, the size of which becomes comparable to the size of the BEC. We study their life time in the BEC and the coupling between the electron and phonons in the BEC [3]. So the single electron that we prepare in a quantum gas allows nicely to study the transition from two- to few- to many-body interaction.
As an outlook, the trapping of a full condensate inside a Rydberg atom of high principal quantum number and the imaging of the Rydberg electron's wavefunction by its impact onto the surrounding ultracold cloud seem to be within reach.

[1] E. Amaldi and E. Segre, Nature 133, 141 (1934)

[2] C. H. Greene, et al. PRL. 85, 2458 (2000); V. Bendkowsky et al., Nature 458, 1005 (2009)
[3] W. Li, et al., Science 334, 1110 (2011)
[4] J . B. Balewski, A. T. Krupp, A. Gaj, D. Peter, H. P. Büchler, R. Löw, S. Hofferberth, T. Pfau, Nature 502, 664 (2013)
Host: Saffman
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