Condensed Matter Seminar
This afternoon’s Condensed Matter seminar. Note that Condensed Matter seminars now take place in C36 Physics.
Title: Non-equilibrium phase transition to the polariton optical parametric oscillator regime
Speaker: Dr Kirsty Dunnett, UCL
Venue: C36 Physics
Time: 3pm
Exciton-polaritons are the quasi-particles that form when cavity photons couple strongly to quantum well excitons in semiconductor microcavities. When a pump laser is applied resonantly to the lower polariton dispersion, a phase transition to the polariton optical parametric oscillator regime, with new, macroscopically occupied `signal’ and `idler’ modes, can occur. Keldysh Green’s functions are used to study this phase transition and an effective chemical potential is identified; the phase transition occurs when the effective chemical potential crosses the normal modes [1].
The `signal’ mode occurs near the minimum of the lower polariton dispersion. A simple method to determine the signal momentum is proposed and the predictions compared with numerical integration of the complex Gross-Pitaevskii equations describing the system. At weak pump strengths, the signal momentum is found best by linear response analysis of the three mode description, while at higher pumping, a linear response analysis of the single pump mode gives best agreement with the numerical simulations.
[1] Dunnett and Szymanska, `Keldysh field theory for non-equilibrium condensation in a parametrically pumped polariton system’, PhysRevB.93.195306.
Grainne Wilinson
Congratulations
Congratulations to Helen McAlley who has recently become engaged to Rob Donnelly, love and best wishes for a great future together from everyone in Physics.
Lynne Haley
Bike Racks
Please do not secure your bicycle to the hand rails of the ramp leading to the Physics entrance. This impedes anyone who needs the rail and access for wheelchairs etc. There are bike racks in Bowland college quads and adjacent to the cTap building. See the University sustainability web pages for more information on the cycling policy and storage. If there is a persistent problem Security will remove secured bicycles.
Shonah Ion
Theoretical Particle Cosmology Group Seminar
Date: Tuesday 6th December 2016
Time: 14.00
Location: C36
Physics Mindaugas Karciauskas – University of Jyvaskyla, Finland
Electroweak Vacuum Stability During Preheating
Abstract: With the discovery of the Higgs boson and its mass measurement it became clear that we might be living in a false vacuum state. Although this state is relatively stable, it is not clear how it could have survived destabilising effect of inflation. This can be explained if we realise that the inflaton must unavoidably couple to the Higgs field, providing a huge positive contribution to the effective mass term of the latter. Unfortunately, the same interactions which save electroweak vacuum during inflation play a destabilising role afterwards. In this talk I discuss this scenario and show that there is a window of parameter space which allows a safe transition from inflation into reheating.
John McDonald
Chemistry Seminar
Chemistry at Lancaster Invites you to a seminar on – Wednesday 16th November 14:00-15:00
“Near-Ambient Pressure X-Ray Photoelectron Spectroscopy: An in-situ probe of surface chemistry”
Dr Alex Walton from the school of Chemistry, University of Manchester TBC
http://www.chemistry.manchester.ac.uk/people/staff/profile/?ea=alex.walton&pg=1
All staff and doctoral students welcome. Please RSVP to c.a.cook@lancaster.ac.uk for catering purposes.
Grainne Wilkinson
Theoretical Particle Cosmology Group Seminar
Date: Tuesday 25th October 2016
Time: 14.00
Location: C36
Physics
Jinsu Kim
Korean Institute of Advanced Studies (KIAS), Seoul
Higgs inflation with Higgs portal interactions
Abstract: Amongst various inflationary models, the most phenomenologically interesting model would be the Higgs inflation due to its minimality and the possibility of a connection between low energy physics and high energy physics. In this talk, after a brief introduction of the Higgs inflation in the Standard Model (SM), we discuss whether the Higgs inflation can be realised in the presence of the Higgs portal interactions. In particular, we show that the Higgs portal interactions involving extra dark Higgs field can save generically the original Higgs inflation from the problem of a deep non-SM vacuum in the SM Higgs potential. The effect of Higgs portal interactions may lead to a larger tensor-to-scalar ratio, by adjusting relevant parameters in wide ranges, some region of which can be probed at future colliders.
John McDonald
Observational Astrophysics Seminar
Title: The role of gas flows in driving galaxy evolution: clues from the cold interstellar medium
Speaker: Amelie Saintonge (UCL)
Time: 3pm on 8th November 2016
Venue: Physics C36
Abstract:
Observations of molecular gas in distant galaxies are experiencing a coming-of-age, transitioning from a “discovery” to a “survey” mode. New and upgraded facilities are now making it possible to survey molecular gas efficiently in large galaxy samples, and these observations are proving to be critical in refining our general picture of galaxy evolution. In this talk, I will review recent results from the two largest surveys for molecular gas in normal star-forming galaxies, the redshift z=0 IRAM-30m COLD GASS survey and the redshift z=1-2 IRAM-PdBI PHIBSS survey, and show how they combine to lend strong support in favour of the “equilibrium” model for galaxy evolution, under which most of galaxy evolution is regulated by gas inflows and outflows, and by the efficiency of the star formation process.
Steve Williams
Physics and Isolab weekly updates
Please see below details of scheduled works on the Physics refurbishment and Isolab projects for next week.
Physics scheduled works
Section 2:
• M&E isolations and strip out
• External surface water drain connection
• Soft strip demolition
• External scaffolding
Isolab scheduled works
• Electrical testing/commissioning
• Mechanical testing/commissioning
• E.M Shielding working floor bolt details
• Clear coats to internal walls
• Ground workers on external area prep/paving and service trench works
• No noisy or disruptive works to Isolab internally, but ground workers will be using a stihl saw on the service trench works
Should you have any queries regarding these projects please contact the Senior Project Manager, Helen Wood, via the Facilities Helpdesk on facilities.helpdesk@lancaster.ac.uk or 01524 593333.
Madeline Asquith
Space Physics seminar: Tue 25th Oct
Space Science Seminar: Gas Giant aeronomy: Earth-like or alien?
Date: Tue 25 October 2016, 1400-1500
Venue: Charles Carter, A16
Speaker: Dr Tom Stallard (University of Leicester)
Abstract:
At the Earth, thanks to a century of investigation, our understanding of the upper atmosphere is relatively strong, though it remains a field of significant scientific intrigue. However, for the Gas Giants like Jupiter, Saturn and Uranus, our understanding is much more limited. Thanks to a combination of spacecraft and Earth-based observations, we have been able to observe and attempt to understand the aurora of these planets over the past couple of decades, but measurements of the underlying atmospheres have proven more difficult.
Until recently, the non-auroral ionospheres and thermospheres have been modelled and observed to be relatively quiescent, but we now that these findings are almost entirely due to lack of resolution. In this seminar, I will present some of the Gas Giant aeronomy communities recent observations and models, that reveal the upper atmospheres of these worlds to be complex and confusing. Some features are eerily like those observed on Earth, while others appear, at first look, entirely alien. http://www.lancaster.ac.uk/physics/about-us/events/?view=fulltext&id=d.en.289567
Sarah Badman