The SEMPARIS seminar webserver hosts annoucements of all seminars taking place in Paris area, in all topics of physics, mathematics and computer science. It allows registered users to receive a selection of announcements by email on a daily or weekly basis, and offers the possibility to archive PDF or Powerpoint files, making it available to the scientific community. [ More information ]
Upcoming Seminars at LPTHE  
[ scheduler view ] 
Thursday 24 January 2019, 10:00 at
LPTHE,
bibliothèque du LPTHE, tour 1314, 4ème étage ( Attention, lieu inhabituel ! )  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  We will analyze the renormalization group (RG) flow of field theories with quenched disorder, in which the couplings vary randomly in space. We analyze both classical (Euclidean) disorder and quantum disorder, emphasizing general properties rather than specific cases. The RG flow of the disorderaveraged theories takes place in the space of their coupling constants and also in the space of distributions for the disordered couplings, and the two mix together. We write down a generalization of the CallanSymanzik equation for the flow of disorderaveraged correlation functions. We find that local operators can mix with the response of the theory to local changes in the disorder distribution, and that the generalized CallanSymanzik equation mixes the disorder averages of several different correlation functions. For classical disorder we show that this can lead to new types of anomalous dimensions and to logarithmic behavior at fixed points. For quantum disorder we find that the RG flow always generates a rescaling of time relative to space, which at a fixed point generically leads to Lifshitz scaling. The dynamical scaling exponent z behaves as an anomalous dimension and we compute it at leading order in perturbation theory in the disorder for a general theory. We also find in quantum disorder that local operators mix with nonlocal (in time) operators under the RG, and that there are critical exponents associated with the disorder distribution that have not previously been discussed. (based on 1803.08534 ) 
Thursday 24 January 2019, 11:40 at
LPTHE,
bibliothèque du LPTHE, tour 1314, 4eme étage ( Attention, lieu inhabituel ! )  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  Finding de Sitter compactifications of string theory has long been a challenge. They are known to require quantum corrections, or orientifold planes, or both. Most existing models rely on effective fourdimensional actions, or work with the tendimensional action but involve 'smearing' the internal Oplanes. After a brief review of such efforts, we present some new numerical solutions with localized and backreacted O8planes. While the solution is singular and stronglycoupled near one of the O8s, it exhibits the same behavior observed for such objects in flat space and in a variety of AdS solutions in various dimensions, with solid holographic crosschecks. Away from the O8s the solution can be made parametrically weaklycoupled thanks to some moduli, whose nature might however be changed by string theory corrections. 
Friday 25 January 2019, 11:00 at LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmechhepthmathph 



Abstract:  Bipartite entanglement entropy is a convenient observable to characterise critical and topological phases of matter. Despite numerous recent efforts, it remains a challenge to obtain both analytical results as well as experimental measurements of this quantity, even for simple systems. Some progress has been achieved recently by realising that in specific cases, e.g. for N noninteracting particles, the entanglement entropy is directly proportional to the number vari ance in the large N limit [1]. This number variance corresponds to the variance of the number of particles in a given domain, an observable much easier to measure experimentally. In this talk I will present a system of noninteracting fermions in two dimensions trapped by an harmonic potential and rotating at constant frequency. I will first show that the groundstate of this model can be mapped to the socalled complex Ginibre ensemble of Random Matrix Theory (RMT). Then I will use RMT techniques to obtain both the entanglement en tropy and the number variance for the fermions in a disk [2]. This computation remains valid for any number N of particles. In the large N limit, we show that the proportionality between number variance and entanglement entropy holds in the bulk, i.e. far enough from the edge of the density while it breaks down at this edge. References : [1] I. Klich, L. Levitov, Quantum noise as an entanglement meter, Phys. Rev. Lett. 102, 100502 (2009); [2] B. LacroixAChezToine, S. N. Majumdar and G. Schehr, Entanglement Entropy and Full Counting Statistics for 2dRotating Trapped Fermions, arXiv preprint 1809.05835, (2018). 
Tuesday 29 January 2019, 14:00 at LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  A rather minimal possibility is that dark matter consists of the gauge bosons of a spontaneously broken symmetry. Here we explore the possibility of detecting the gravitational waves produced by the phase transition associated with such breaking. Concretely, we focus on the scenario based on an SU(2) group and argue that it is a case study for the sensitivity of future gravitational wave observatories to phase transitions associated with dark matter. This is because there are few parameters and those fixing the relic density also determine the effective potential establishing the strength of the phase transition. Particularly promising for LISA is the supercool dark matter regime, with DM masses above O(100) TeV, for which we find that the gravitational wave signal is notably strong. In our analysis, we include the effect of astrophysical foregrounds, which are often ignored in the context of phase transitions. (based on 1809.01198 ) 
Friday 1 February 2019, 11:00 at LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmech 



Abstract:  Understanding the statistical properties of complex and/or random landscapes in highdimensional spaces is a central problem in a variety of different contexts, from glassy systems to computer science, ecology and biology. Among these properties, an important role is played by the statistics of the number of stationary points, which is expected to be relevant in determining the evolution of local dynamics within the landscape. In this talk, I will discuss the calculation of the typical number of local minima of the energy landscape of a simple model, which captures the competition between a deterministic ‘signal’ term and a noisy contribution. The model is obtained adding to the spherical pspin Hamiltonian a term favoring configurations that are aligned to a given configuration on the sphere (the signal), and reproduces the spikedtensor model for a specific choice of parameters. I will describe the phase transitions that occur in the structure of the landscape when changing the signaltonoise ratio, and provide some details on the calculation of the quenched complexity, that is performed using a replicated version of the KacRice formula. The talk is based on joint work with Gérard Ben Arous, Giulio Biroli and Chiara Cammarota. 
Friday 1 February 2019, 14:00 at LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  In March 2018 the EDGES experiment has reported the discovery of a 21cm signal in absorption between redshift 20 and 15. This measurement, if confirmed, is fundamental for astrophysics because it can give us information about the epoch of reionization soon after the formation of first stars and galaxies. This talk is organised in three parts. In the first part I will present the EDGES experiment and the procedure the collaboration has used to extract the broad absorption profile from strong foreground of galactic synchrotron emission. Then I will review the physics of the 21cm signal and the history of the InterGalactic Medium (IGM) properties assuming a LambdaCDM Universe. Finally, I will conclude with a simple application of this measurement to set bounds on the Dark Matter (DM) properties. In particular, annihilating DM particles produce significant heating of the IGM erasing the absorption feature measured by EDGES. These new limits on the annihilation cross section into standard model particles are comparable to the strongest ones from all other observables. 
Thursday 7 February 2019, 10:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 7 February 2019, 11:40 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 21 February 2019, 10:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 21 February 2019, 11:40 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Friday 22 February 2019, 11:00 at LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmechhepthmathph 



Abstract:  Floquet topological insulators describe independent electrons on a lattice driven out of equilibrium by a timeperiodic Hamiltonian, beyond the usual adiabatic approximation. In dimension two such systems are characterized by integervalued topological indices associated to the unitary propagator, alternatively in the bulk or at the edge of a sample. In this talk I will give new definitions of the two indices, relying neither on translation invariance nor on averaging, and show that they are equal. In particular disorder and defects are intrinsically taken into account, even in the mobility gap regime. Finally indices can be defined when two driven sample are placed next to one another either in space or in time, and then shown to be equal. The edge index is interpreted as a quantized pumping occurring at the interface with an effective vacuum, and can also be estimated numerically. 
Thursday 14 March 2019, 10:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 14 March 2019, 11:40 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 21 March 2019, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepth 


Thursday 28 March 2019, 11:40 at IHP, 201  RENCTHEO (Rencontres Théoriciennes)  hepth 


Friday 29 March 2019, 11:00 at LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmechhepthmathmathphmath.AG 


Thursday 4 April 2019, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepth 


Thursday 11 April 2019, 11:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 11 April 2019, 11:40 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 9 May 2019, 10:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 9 May 2019, 11:40 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 16 May 2019, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepth 


Thursday 20 June 2019, 10:00 at IHP, Salle 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 27 June 2019, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepth 



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