SCHOOL OF PHYSICS :: Seminars

Seminars

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Tue Jun 06, 2023 (1402/3/16)

	Jun 06 1402/3/16	14:00	A test of the standard cosmological model in the redshift bins Show Abstract Abstract:Flat Î?CDM cosmology is specified by two constant fitting parameters in the late-time Universe, the Hubble constant H_0 and matter density $\Omega_{m0}$. While these parameters are mathematically constant, they do not need to be observationally constant unless the EoS or model accurately describes the Universe. In this work, we have shown that using observational data at different redshifts shows that the Î?CDM model parameters are redshift dependent. In other words, we have confirmed that observed data exhibit an increasing $\Omega_{m0}$ (decreasing H_0) trend with increasing redshift bins. Lecturer(s): Saeed PourOjaghi From : School of Physics, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue May 30, 2023 (1402/3/9)

	May 30 1402/3/9	14:00	Exorcising the Ghost Condensate Dark Energy with a Sextic Dispersion Relation Show Abstract Abstract:The universe's current acceleration is a pretty recent phenomenon in cosmological time scales. This means that the modes that have left our horizon since the beginning of the contemporary acceleration phase, have not really reached the exact IR limit. Noting this observation, we reconsider the possibility of having a ghost condensate as dark energy with a sixth-order dispersion relation. Looking at the three-point function of such a theory, we obtain the constraints on the coefficient of the sixth-order dispersion relation to avoid strong coupling. We notice that such a constraint can be easily satisfied, without fine-tuning. Such a ghost condensate, if coupled to the standard model fields, induces a constant Lorentz-violating spin-dependent force, which can gravitate or anti-gravitate. The Newtonian potential is modified with an oscillatory behavior at distance scale $M_{\rm Pl}/M^2$ at the time scale $M_{\rm Pl}^2/M^3$, where $M^2$ is the expectation value of the ghost field velocity, i.e. $\langle\dot{\phi}\rangle=M^2$. Lecturer(s): AbdolReza Yousefi-Sostani From : School of Physics, IPM Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue May 23, 2023 (1402/3/2)

	May 23 1402/3/2	14:00	Cosmic voids are emptier in the presence of symmetron's domain walls Show Abstract Abstract:Date and time Today, 23rd of May 2023 (2nd of Khordad, 1402), 2:00 pm (Tehran zone) Link https://www.skyroom.online/ch/schoolofphysics/highenergyseminar Abstract The symmetron field has an environment (density) dependent behavior which is a common feature of the models with the screening mechanism and results in a rich phenomenology. This model can produce domain walls between regions with different densities. We consider this aspect and study the physics of domain walls in between (underdensity) voids and (overdensity) halo structures. The (spherical) domain walls exert a repulsive force on a test mass outside of the wall while a test mass inside of the wall sees no force. This makes the structures outside the voids go further to a larger radius. Effectively, this means the voids are becoming larger in this scenario in comparison to the standard model of cosmology. Interestingly, this makes voids emptier which may shed light on Peebleâ??s void phenomenon. Lecturer(s): Bahar Nosrati From : Shahid Beheshti University Research Group: HEPCO Group Weekly Seminar More Info. : Link
Wed May 10, 2023 (1402/2/20)

	May 10 1402/2/20	18:00	Uncovering hidden neuronal microcircuits using Boltzmann like correlations, a unified framework Show Abstract Abstract:The information transfer and processing in our brain relies on cells called neurons. They are connected to each other through connections called synapse, and form an interconnected complex network, known as gray matter. Each neuron receives signals from its upstream neurons, generates a spike, and passes it to many downstream neurons. To understand this complex structure, one should have learnt the connectivity map of neurons, in a living brain. However, it is practically impossible to record from one neuron and all its hidden inputs to determine the influential synapses which dominate the activity of that neuron. Although there are methods to find the connectivity among recorded (observed) neurons, the majority of downstream neurons remain unobserved. Here, we find the analytical input-output relation which describes how a specific input to a neuron controls statistics of its spiking pattern. Then, using this analytics, we connect the hidden microcircuits which are shared by two or more neurons with the observed correlation between their spiking patterns. We present a guide map in the space of neural interactions (i.e pairwise and triple-wise correlations) to infer the influential hidden circuits from data. We verify the validity of the guide map by extensive simulations, using multicompartmental neuron models of Blue Brain Project. Applying the guide map to monkey and mouse, we observed the hidden circuitry of excitatory inputs shared between each pair of three neurons is the motif behind most of the data. We hope experimentalists use our guide-map, to reveal the hidden microcircuits behind their data. Lecturer(s): Seyyed Nader Rasuli From : IPM, School of Physics Research Group: Physics Colloquium More Info. : Link
Tue May 09, 2023 (1402/2/19)

	May 09 1402/2/19	14:00	Relaxing the Cosmological Tensions Show Abstract Abstract:The standard cosmological model is in the midst of a stress test, thanks to the tensions between supernovae-based measurements of the Hubble constant, $H_0$, and the variance of matter power spectrum at 8/h Mpc, $\sigma_8$, and the inference of these parameters from the $\Lambda$CDM model. In the first part of my talk, I will try to address the former discrepancy known as the $H_0$ tension. In particular, since numerous explanations for the present-day cosmic acceleration require the presence of a new fundamental scalar field, as do Early Dark Energy (EDE) solutions to the Hubble tension, this raises the possibility that multiple fields cooperatively contribute to the dark energy component in bursts throughout cosmic time due to distinct initial conditions and couplings. Here, this Cascading Dark Energy (CDE) scenario is illustrated through a realization that effectively reduces to a two-field model, with two epochs in which dark energy is cosmologically significant. The model is compared to measurements of the CMB, baryon acoustic oscillations, and observations of Type-Ia supernovae. It is found that this scenario ameliorates the Hubble tension, improving over purely late-time models of dark energy, and the agreement between the galaxy survey measurements of baryon acoustic oscillations. In the second part of my talk, I will try to address the $\sigma_8$ tension, exploiting the dark matter with varying viscosity. We notice that the time-varying scenarios reduce the $\sigma_8$ tension even better than the constant bulk viscosity case. Lecturer(s): Amjad Ashoorioon From : IPM, School of Physics Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue May 02, 2023 (1402/2/12)

	May 02 1402/2/12	14:00	Decoherence effects in neutrino oscillations - a QFT approach Show Abstract Abstract:In the QFT approach to neutrino oscillations, neutrino production, propagation, and detection are considered as a single process. This formalism allows to take into account in a well defined procedure possible decoherence effects, both at the quantum level as well as due to classical averaging of the amplitude-squared. We extend this method and apply it to the particular case of reactor oscillation experiments and Gallium source experiments. We show that quantum decoherence effects are many orders of magnitude smaller than classical averaging effects and therefore unobservable. Lecturer(s): Thomas Schwetz-Mangold From : Institute for Astroparticle Physics, Karlsruhe Institute of Technology Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Apr 25, 2023 (1402/2/5)

	Apr 25 1402/2/5	14:00	Dipole Cosmology: Towards beyond FLRW framework Show Abstract Abstract:There are various, but still tentative, observations hinting to existence of a cosmic flow or cosmic dipole (preferred direction) in cosmological backgrounds. If substantiated, these observations suggest developing cosmological modeling beyond the usual FLRW setting. I present "dipole cosmological principle" as the most symmetric paradigm that generalizes the FLRW ansatz and allows for cosmic dipoles. We construct a general dipole cosmology framework and analyze Einstein equations for the dipole cosmology which beside usual FLRW fields involve cosmic shear (parametrizing the anisotropy in the metric) and the tilt (parametrizing the cosmic flow or cosmic dipole). These equations are still ordinary differential equations due to homogeneity of the dipole cosmology setting. We study dynamics of the expansion rate, anisotropic shear and tilt, in various examples. One our key results is that the cosmic flow (tilt) can grow in time even while the anisotropy (shear) dies down. Remarkably, this can happen even in an era of late time acceleration. The other key result is that FLRW framework is unstable with respect to perturbations associated with cosmic dipoles. This means having a homogeneous and isotropic cosmology is not a theoretically natural choice. Lecturer(s): Shahin Sheikh-Jabbari From : IPM, School of Physics Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Apr 18, 2023 (1402/1/29)

	Apr 18 1402/1/29	14:00	Neutrino Non-standard interactions with arbitrary couplings to u and d quarks Show Abstract Abstract:Date and time Tuesday, 18th of April 2023 (29th of Farvardin, 1402), 2:00 pm (Tehran zone) Link https://www.skyroom.online/ch/schoolofphysics/highenergyseminar Abstract We introduce a model for Non-Standard neutral current Interaction (NSI) between neutrinos and the matter fields, with an arbitrary coupling to the up and down quarks. The model is based on a new U(1) gauge symmetry with a light gauge boson that mixes with the photon. We show that the couplings to the u and d quarks can have a ratio such that the contribution from NSI to the Coherent Elastic Neutrino-Nucleus Scattering (CEÎ½NS) amplitude vanishes, relaxing the bound on the NSI from the CEÎ½NS experiments. Additionally, the deviation of the measured value of the anomalous magnetic dipole moment of the muon from the standard-model prediction can be fitted. Lecturer(s): Yasaman Farzan From : IPM, School of Physics Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Apr 11, 2023 (1402/1/22)

	Apr 11 1402/1/22	14:00	Revisiting pseudo-Dirac neutrino scenario after recent solar neutrino data Show Abstract Abstract:Date and time Tuesday, 11th of April 2023 (22nd of Farvardin, 1402), 2:00 pm (Tehran zone) Link https://www.skyroom.online/ch/schoolofphysics/highenergyseminar Abstract It is still unknown whether the mass terms for neutrinos are of Majorana type or of Dirac type. An interesting possibility, known as pseudo-Dirac scheme combines these two with a dominant Dirac mass term and a subdominant Majorana one. As a result, the mass eigenstates come in pairs with a maximal mixing and a small splitting determined by the Majorana mass. This will affect the neutrino oscillation pattern for long baselines. We revisit this scenario employing recent solar neutrino data, including the seasonal variation of the 7Be flux recently reported by BOREXINO. Lecturer(s): Saeed AnsariFard From : IPM, School of Physics Research Group: HEPCO Group Weekly Seminar More Info. : Link
Tue Apr 04, 2023 (1402/1/15)

	Apr 04 1402/1/15	14:00	Shallow Water Memory: Stokes and Darwin Drifts Show Abstract Abstract:In this talk, we will show how the atmosphere, oceans, water in a pool, and many fluids around us are described based on a gauge theory similar to electromagnetism. On the other hand, as a result of this formulation, we show how the so-called (displacement) memory effect, which people seek to detect in gravitational waves (for example by LIGO, VIRGO, LISA, etc.), also naturally appears in a shallow water system. Lecturer(s): Vahid Taghiloo From : IPM & IASBS Research Group: HEPCO Group Weekly Seminar More Info. : Link
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