# NBI-Theoretical Particle Physics and Cosmology

## Seminars and Events: Spring 2014

These are past events. View upcoming events.

• January 2014
• ### HET journal club seminar

Fb-6, Wednesday 8 Jan at 13:15

### Martin Heinze (Humboldt University)

Static Gauge and Energy Spectrum of Single-mode Strings in AdS_5xS^5

# HET journal club seminar

## Static Gauge and Energy Spectrum of Single-mode Strings in AdS_5xS^5

### Abstract:

In my talk I report on recent progress in calculation of the first quantum corrections to the spectrum of short strings in AdS_5xS^5 from first principles. Restricting ourselves to the bosonic sector, we employ static gauge and quantize in a minisuperspace approach, in which we consider only a single AdS_5 string mode excitation plus arbitrary particle like zero-modes in AdS_5xS^5. We determine the quantum spectrum to the next-to-next-to-leading order in the large 't Hooft coupling expansion. Arguing for an ordering prescription which should arise from supersymmetrization, we indeed recover the integrability based predictions for the spectrum of the lightest excitation, dual to the Konishi field scaling dimensions. Higher excitations fail to agree, which is shown to be a consequence of the string mode truncation employed. Despite this simple setup, our system reveals intriguing features, such as a close connection to particles in AdS_6, classical integrability and preservation of the isometries of AdS_5xS^5 at the quantum level.

### Details

Date: Wednesday 8 Jan

Time: 13:15

Place: Fb-6

×
• ### Special Discovery-HET Seminar

Aud A, Monday 13 Jan at 14:15

### Julien Lesgourgues (CERN/EPFL)

What can the CMB tell us about the nature of dark matter

# Special Discovery-HET Seminar

## What can the CMB tell us about the nature of dark matter

### Details

Date: Monday 13 Jan

Time: 14:15

Place: Aud A

×
• ### HET journal club seminar

Fb-6, Wednesday 15 Jan at 13:15

### Pawel Caputa (University of the Witwatersrand, Johannesburg)

Aspects of entanglement entropy in and out of equilibrium

# HET journal club seminar

## Aspects of entanglement entropy in and out of equilibrium

### Abstract:

Based on hep-th/1306.4974 and hep-th/1309.7852

### Details

Date: Wednesday 15 Jan

Time: 13:15

Place: Fb-6

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• ### Discovery-HET Seminar

Aud. A, Thursday 16 Jan at 14:15

### Stephan Stieberger

On Superstring/Supergravity Mellin Correspondence in Grassmannian Formulation

# Discovery-HET Seminar

## On Superstring/Supergravity Mellin Correspondence in Grassmannian Formulation

### Abstract:

At the tree level, the maximally helicity violating amplitudes of N gauge bosons in open superstring theory and of N gravitons in supergravity are known to have simple representations in terms of tree graphs. For superstrings, the graphs encode integral representations of certain generalized Gaussian hypergeometric functions of kinematic invariants, while for supergravity, they represent specific kinematic expressions constructed from spinor-helicity variables. We establish a superstring/supergravity correspondence for this class of amplitudes, by constructing a mapping between the positions of gauge boson vertices at the disk boundary and the helicity spinors associated to gravitons.

Furthermore, we extend this correspondence of supergravity and superstring amplitudes to the case of arbitrary helicity configurations. The amplitudes are discussed in the framework of Grassmannian varieties. We generalize Hodges' determinant to a function of two sets of independent coordinates and show that tree-level supergravity amplitudes can be obtained by contour integrations of both sets in separate Grassmannians while in superstring theory, one set of coordinates is identified with string vertex positions at the disk boundary.

After replacing vertex positions by a larger set of N(N-3)/2 coordinates, the superstring amplitudes become (multiple) Mellin transforms of supergravity amplitudes, from the projective space into the dual Mellin space of N(N-3)/2 kinematic invariants. Similarly, inverse Mellin transforms transmute open superstrings into supergravity.
We elaborate on the properties of multiple Mellin and inverse Mellin transforms in the framework of superstring/supergravity correspondence.

### Details

Date: Thursday 16 Jan

Time: 14:15

Place: Aud. A

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• ### Discovery-HET Seminar

Aud M, Tuesday 21 Jan at 14:15

### Song He

S-matrices of massless particles

# Discovery-HET Seminar

## S-matrices of massless particles

### Abstract:

I will present compact formula for the tree-level S-matrix of scalar theory, Yang-Mills and gravity in arbitrary spacetime dimension, in terms of integrals over punctures on a sphere restricted to satisfy a set of equations. The new formula for S-matrices of scalars, gluons and gravitons are closely related to each other, which makes non-trivial properties of the amplitudes, such as KLT relations, BCJ color-kinematics duality and double-copy relations, manifest. The formula also has implications for the S-matrix of string theories in twistor space and in the pure spinor formalism.

### Details

Date: Tuesday 21 Jan

Time: 14:15

Place: Aud M

×
• ### HET journal club lunch

Bk2, Wednesday 22 Jan at 12:30

# HET journal club lunch

### Details

Date: Wednesday 22 Jan

Time: 12:30

Place: Bk2

×
• ### Discovery-HET Seminar

Aud M, Thursday 23 Jan at 14:15

### Martin Beneke

Anomalous magnetic moment of the muon and penguin loops in the Randall-Sundrum model

# Discovery-HET Seminar

## Anomalous magnetic moment of the muon and penguin loops in the Randall-Sundrum model

### Abstract:

The Randall-Sundrum model with Standard Model fields in the
bulk of a warped five-dimensional space-time provides a
simultaneous solution to the gauge and flavour hierarchy
problems. While the tree-level phenomenology of this model has
been widely studied, relatively little has been known about
processes that are entirely loop-induced. In this seminar
I describe the calculation of such processes in a framework
that treats the model as a full-fledged 5D quantum field
theory avoiding the introduction of Kaluza-Klein
decompositions. The results focus on the muon anomalous
magnetic moment and the radiative lepton-flavour-violating
decay mu -> e gamma.

### Details

Date: Thursday 23 Jan

Time: 14:15

Place: Aud M

×
• ### Discovery Colloquium

Aud A, Tuesday 28 Jan at 15:15

### Olga Botner

Catching cosmic clues in the ice - recent results from IceCube

# Discovery Colloquium

## Catching cosmic clues in the ice - recent results from IceCube

### Abstract:

IceCube is a neutrino observatory located deep in the Antarctic glacier close to the geographical South Pole. Close to a gigaton of ice has been instrumented with optical sensors with the primary goal of searching for neutrinos from the still unknown sources of the highest-energy cosmic rays. Last year, IceCube observed for the first time ever a handful of high-energy neutrinos which must have originated outside the solar system. The discovery was named the 2013 Breakthrough of the Year by the British magazine Physics World. It is the first necessary step to actually achieve the dream of charting the places in the universe able to accelerate hadrons to energies over a million times higher than those at the LHC. The science goals of IceCube extend beyond astrophysics: IceCube is also a powerful tool for searches of dark matter and can be used to study phenomena connected to the neutrinos themselves, like neutrino oscillations. The talk will be an update on the most recent results from IceCube.

### Details

Date: Tuesday 28 Jan

Time: 15:15

Place: Aud A

×
• ### HET journal club seminar

Fb-6, Wednesday 29 Jan at 13:15

### Leonid Chekhov (Long-term visitor at NBI; Steklov Math Inst.; Loughborough U.)

Quantum Riemann surfaces and beta ensembles (Part 1 of 2)

# HET journal club seminar

## Quantum Riemann surfaces and beta ensembles (Part 1 of 2)

### Details

Date: Wednesday 29 Jan

Time: 13:15

Place: Fb-6

×
• ### Discovery-HET Seminar

Aud A, Thursday 30 Jan at 14:15

### David Vegh

Holographic massive gravity

# Discovery-HET Seminar

## Holographic massive gravity

### Abstract:

We study finite density holographic theories on a background lattice. The presence of the lattice induces an effective mass for the bulk graviton via a gravitational version of the Higgs mechanism. Momentum is not conserved and the conductivity in the boundary theory exhibits a Drude peak.

### Details

Date: Thursday 30 Jan

Time: 14:15

Place: Aud A

×
• February 2014
• ### HET journal club lunch

Fb-6, Wednesday 5 Feb at 12:30

# HET journal club lunch

### Details

Date: Wednesday 5 Feb

Time: 12:30

Place: Fb-6

×
• ### Discovery-HET Seminar

Aud A, Thursday 6 Feb at 14:15

Membranes from monopole operators in ABJM theory: Large angular momentum and M-theoretic AdS4/CFT3

# Discovery-HET Seminar

## Membranes from monopole operators in ABJM theory: Large angular momentum and M-theoretic AdS4/CFT3

### Abstract:

In the talk, I will consider states with large angular momentum to
facilitate the study of the M-theory regime of the AdS4/CFT3 correspondence
(duality between M-theory on $AdS_4 \times S^7/Z_k$ and ABJM theory
with gauge group $U(N)\times U(N)$ and level $k$,
where $k$ is finite and $N$ is large).
In particular I will discuss near-BPS operators in ABJM theory
which correspond to states of membranes with large angular momenta on AdS.
The talk will be based on my work with Stefano Kovacs(DIAS) and Yuki Sato
(Wits University).

### Details

Date: Thursday 6 Feb

Time: 14:15

Place: Aud A

×
• ### HET journal club lunch

Fb-6, Wednesday 12 Feb at 12:30

# HET journal club lunch

### Details

Date: Wednesday 12 Feb

Time: 12:30

Place: Fb-6

×
• ### Discovery-HET Seminar

Auditorium A, Thursday 13 Feb at 14:15

### Koichi Murakami

Multiloop amplitudes of light-cone gauge bosonic string field theory in noncritical dimensions

# Discovery-HET Seminar

## Multiloop amplitudes of light-cone gauge bosonic string field theory in noncritical dimensions

### Abstract:

Superstring field theory has not been established yet, mainly because of a divergence problem called the contact term problem", which occurs even at the tree-level. This happens in the light-cone gauge formulation as well as gauge invariant one. In order to deal with this divergence for the light-cone gauge NSR superstring field theory, we have proposed the regularization scheme in which the spacetime dimensions is shifted to a large negative value. So far we have verified that our dimensional regularization works for the tree-level amplitudes. As a first step towards the examination whether the dimensional regularization works for the multiloop amplitudes, we study in this work the multiloop amplitudes of the light-cone gauge closed bosonic string field theory in noncritical dimensions. We show that the amplitudes can be recast into a BRST invariant form by adding a nonstandard worldsheet theory for the longitudinal variables and the reparametrization ghost system. I would also like to comment on the superstring extension in progress.
This talk is based on the collaboration with Nobuyuki Ishibashi (University of Tsukuba).

### Details

Date: Thursday 13 Feb

Time: 14:15

Place: Auditorium A

×
• ### Discovery-HET Seminar

Aud A, Tuesday 18 Feb at 14:15

### Assaf Ben-David (NBIA)

Searches for Mirror-Parity and Stringy Topologies in the CMB

# Discovery-HET Seminar

## Searches for Mirror-Parity and Stringy Topologies in the CMB

### Abstract:

If inflation was relatively short, signatures of pre-inflationary physics could be observed on the largest scales of the CMB, breaking statistical isotropy. These scales, on which the cosmic variance is large, indeed show several anomalies. In this talk I will describe two searches for such isotropy-breaking evidence. One is the search for anomalous mirror-parity, motivated by some models of pre-inflationary relics. While past analysis of WMAP data has shown evidence for odd parity, I will present a closer examination of the anomaly on Planck data, shedding more light on this claim. The other search I will describe is for a non-trivial topology of the universe, which can lead to interesting symmetries in the CMB. I will consider some non-classical topologies allowed in string theory, and describe their observational signatures as well as the searches for these signatures in the CMB data.

### Details

Date: Tuesday 18 Feb

Time: 14:15

Place: Aud A

×
• ### HET journal club seminar

Fb-6, Wednesday 19 Feb at 13:15

### Edvard Musaev (Queen Mary, University of London)

Dimensional reductions of exceptional supergravities

# HET journal club seminar

## Dimensional reductions of exceptional supergravities

### Abstract:

The recently appeared approach of Double Field Theory (or extended geometry) allowed to rewrite low energy effective actions for string and M-theory in a duality covariant way. The price paid was the extension of space coordinates that now transform in a irrep of the corresponding duality group. In this talk we will cover the problem of dimensional reductions in this formalism and show that under Scherk-Schwarz compactification it naturally reproduces the structure of gauged supergravities.

### Details

Date: Wednesday 19 Feb

Time: 13:15

Place: Fb-6

×
• ### HET journal club seminar

Fb-6, Wednesday 26 Feb at 13:15

### Leonid Chekhov (Long-term visitor at NBI; Steklov Math Inst.; Loughborough U.)

Quantum Riemann surfaces and beta ensembles (Part 2 of 2)

# HET journal club seminar

## Quantum Riemann surfaces and beta ensembles (Part 2 of 2)

### Details

Date: Wednesday 26 Feb

Time: 13:15

Place: Fb-6

×
• ### HET Colloquium

Aud A, Thursday 27 Feb at 14:15

### Timothy Hollowood (Swansea University)

Schrodinger's Cat: Wanted Dead or Alive

# HET Colloquium

## Schrodinger's Cat: Wanted Dead or Alive

### Abstract:

I will explain how it is possible to assemble a consistent interpretation of quantum mechanics in a way that has no funny stuff (no brains, no minds, no parallel worlds) but at the same time reproduces the familiar phenomenology of the Copenhagen interpretation for macro-systems. At the same time the Schrodinger equation holds without modification.
The intuition needed comes from the notion of effective theory in QFT but the ideas and formalism are very simple. I show how the measurement problem is solved and discuss the EPR thought experiment in some detail. If time permits I will explain how the new interpretation has something interesting to say about the black hole firewall puzzle.

### Details

Date: Thursday 27 Feb

Time: 14:15

Place: Aud A

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• ### Discovery-HET Seminar

Aud D, Friday 28 Feb at 13:00

### Timothy Hollowood (Swansea University)

Integrability on the World-Sheet

# Discovery-HET Seminar

## Integrability on the World-Sheet

### Abstract:

I will review the idea of deforming the integrable structure on the world sheet of the string in the AdS/CFT correspondence. This leads to a connection between the string theory and generalizations of the well-known sine-Gordon field theory that some remarkable properties. The emphasis will be on giving an overview rather than the technical details.

### Details

Date: Friday 28 Feb

Time: 13:00

Place: Aud D

×
• ### NBIA Colloquium

Aud A, Friday 28 Feb at 14:15

### Marc Barthélémy (CEA Saclay)

How cities develop: a physicist's perspective

# NBIA Colloquium

## How cities develop: a physicist's perspective

### Abstract:

Physical arguments and modeling enable one to understand a number of features of data on urban growth. The first example I shall consider is that a number of quantities, such as the total energy used in transportation, and the length of the street network, display a scaling behavior as a function of the total population and I shall show how the observed nontrivial exponents come about. The second topic will be how to understand the evolution of transportation networks, such as streets and subways.
Refreshments will be served in the NBIA lounge after the talk.

### Details

Date: Friday 28 Feb

Time: 14:15

Place: Aud A

×
• March 2014
• ### HET journal club lunch

Fb-6, Wednesday 5 Mar at 12:30

# HET journal club lunch

### Details

Date: Wednesday 5 Mar

Time: 12:30

Place: Fb-6

×
• ### Discovery/HET Cosmology Seminar

Auditorium M, Tuesday 11 Mar at 11:15

### Jean-Luc Starck

CMB map estimation from WMAP and Planck

# Discovery/HET Cosmology Seminar

## CMB map estimation from WMAP and Planck

### Abstract:

We present the first CMB map reconstructed from both WMAP and
Planck datasets. Using recent statistical tools based
on sparsity, we show that the Galactic barrier can be broken down, so that
we can have a full sky high quality CMB map, for the first time.
In addition, as a result of our novel approach, this high quality map is
free of any significant thermal SZ contamination.
Finally, we present a new method to reconstruct the primordial power
spectrum from WMAP-9yr data.

### Details

Date: Tuesday 11 Mar

Time: 11:15

Place: Auditorium M

×
• ### Discovery-HET Seminar

Auditorium A, Tuesday 11 Mar at 14:15

### Paolo di Vecchia

How to recover unitarity in gravitational high-energy scattering of particles and strings on Dp-branes

# Discovery-HET Seminar

## How to recover unitarity in gravitational high-energy scattering of particles and strings on Dp-branes

### Abstract:

High-energy scattering in a gravitational theory is dominated by graviton exchanges. Since gravitons are coupled to energy, perturbative unitarity is violated. In this talk we will discuss how unitarity is recovered in the scattering of both a particle and a closed string on Dp-branes. In the case of a particle one must re-sum the perturbative series getting the eikonal c-number phase that is unitary. The case of string is more interesting because one gets the eikonal operator that is an operator in the Hilbert space of the string states. In this case, unlike the scattering of a particle, elastic unitarity is violated and, in order to recover the full unitarity, one must include inelastic processes. In this talk the eikonal operator is obtained with a complete string calculation. This allows us to identify the microscopic closed-string states that must be included for satisfying the unitarity requirement for large impact parameter. At the end of the talk we will discuss the lack of unitarity occurring at smaller impact parameters due to the fact that the production of open strings has not been yet properly taken into account.

### Details

Date: Tuesday 11 Mar

Time: 14:15

Place: Auditorium A

×
• ### HET journal club lunch

Fb-6, Wednesday 12 Mar at 12:30

# HET journal club lunch

### Details

Date: Wednesday 12 Mar

Time: 12:30

Place: Fb-6

×
• ### Discovery-HET Seminar

Auditorium A, Thursday 13 Mar at 14:15

### Lorenzo Magnea

The infrared structure of gauge amplitudes and the high-energy limit'

# Discovery-HET Seminar

## The infrared structure of gauge amplitudes and the high-energy limit'

### Abstract:

I will review recent progress in our understanding of the infrared
structure of multi-particle gauge theory amplitudes, paying special
attention to the high-energy (`Regge') limit. For massless gauge theories,
the multi-particle soft anomalous dimension is known to have a remarkably
simple, dipole-like form up to very high orders in perturbation theory,
and subleading multipole corrections are currently a subject of intense
studies. In the high-energy limit, the dipole formula leads to a simple
factorized expression for the amplitude, which automatically implies
Reggeization of singular contributions to t-channel exchanges. Furthermore,
one can study the breakdown of Regge-pole factorization at high energy,
starting at NNLL, and provide explicit expressions for the leading
Regge-cut contributions to high-energy logarithms.

### Details

Date: Thursday 13 Mar

Time: 14:15

Place: Auditorium A

×
• ### Joint Experiment/Theory Seminar

Auditorium A, Friday 14 Mar at 13:15

### Ning Zhou

Search for Dark Matter and invisible Higgs decays using hadronic decays of W and Z

# Joint Experiment/Theory Seminar

## Search for Dark Matter and invisible Higgs decays using hadronic decays of W and Z

### Abstract:

A search is presented for dark matter pair production in association with
a W or Z boson in pp collisions representing 20.3 fb-1 of integrated
luminosity at sqrt(s)=8TeV using data recorded with the ATLAS detector at
the LHC. Events with a hadronic jet with the jet-mass consistent with a W
and Z boson, and with large missing transverse momentum are analyzed. The
data are consistent with the SM expectations. Limits are set on the mass
scale in effective field theories that describe the interaction of dark
matter and SM particles, and the cross section of Higgs decay to invisible
particles in a UV complete theory with the Higgs boson as a light
mediator.

### Details

Date: Friday 14 Mar

Time: 13:15

Place: Auditorium A

×
• ### Informal Discovery Seminar

Auditorium A, Tuesday 18 Mar at 14:15

### Pavel Naselsky

Cosmological Gravitational Waves from BICEP experiment

# Informal Discovery Seminar

## Cosmological Gravitational Waves from BICEP experiment

### Details

Date: Tuesday 18 Mar

Time: 14:15

Place: Auditorium A

×
• ### HET journal club seminar

Fb-6, Wednesday 19 Mar at 13:15

### Esben Mølgaard (CP3-Origins, DIAS, University of Southern Denmark)

Renormalization group flows and the Weyl consistency conditions

# HET journal club seminar

## Renormalization group flows and the Weyl consistency conditions

### Abstract:

In this talk, I will introduce the concept of renormalization group flow and describe the general features that can be found in such flows in (gauge-)Yukawa theories. In perturbation theory, the renormalization group flow is given by the beta functions of the various couplings, and these can be calculated to different loop orders. It will become apparent that it is necessary to have a criterion that can determine the correct way to go to higher order in the multi-coupling loop expansion. I propose that the Weyl consistency conditions are exactly that criterion and present both their derivation and their implication. If there is sufficient time, I will also touch upon how this affects the stability of the standard model vacuum.

My talk is based primarily on
Oleg Antipin, Marc Gillioz, Jens Krog, Esben Mølgaard, and Francesco Sannino, Standard Model Vacuum Stability and Weyl Consistency Conditions," JHEP 1308, 034 (2013a), arXiv:1306.3234 [hep-ph]
Esben Mølgaard and Robert Shrock, "Renormalization-Group Flows and Fixed Points in Yukawa Theories," arXiv:1403.3058 [hep-th]

### Details

Date: Wednesday 19 Mar

Time: 13:15

Place: Fb-6

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• ### Discovery-HET Seminar

Auditorium A, Thursday 20 Mar at 14:15

### Yolanda Lozano (University of Oviedo)

Hints on 5d fixed point theories from non-Abelian T-duality

# Discovery-HET Seminar

## Hints on 5d fixed point theories from non-Abelian T-duality

### Abstract:

In spite of being non-renormalizable 5d gauge theories can be at fixed points at strong coupling, if equipped with specific gauge groups and matter content. Being strongly coupled the AdS/CFT correspondence provides a powerful tool for their study. Starting from the only 5d theory for which the AdS dual is known we use non-Abelian T-duality to generate a new AdS_6 background and explore the properties of its associated dual CFT.

### Details

Date: Thursday 20 Mar

Time: 14:15

Place: Auditorium A

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• ### Discovery-HET Seminar

Aud. D, Friday 21 Mar at 11:15

### Elias Kiritsis (Crete University & CERN & APC, Paris)

The confining trailing string

# Discovery-HET Seminar

## The confining trailing string

### Abstract:

We extend the holographic trailing string picture of a heavy quark to the case of a bulk geometry dual to a confining gauge theory. We compute the classical trailing confining string solution for a static as well as a uniformly moving quark. The trailing string is infinitely extended and approaches a confining horizon, situated at a critical value of the radial coordinate, along one of the space-time directions, breaking boundary rotational invariance. We compute the equations for the fluctuations around the classical solutions, which are used to obtain boundary force correlators controlling the Langevin dynamics of the quark. The imaginary part of the correlators has a non-trivial low-frequency limit, which gives rise to a viscous friction coefficient induced by the confining vacuum. The vacuum correlators are used to define finite-temperature dressed Langevin correlators with an appropriate high-frequency behavior.

### Details

Date: Friday 21 Mar

Time: 11:15

Place: Aud. D

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• ### PhD Defense

Aud. A, Friday 21 Mar at 14:00

# PhD Defense

## Andreas Vigand Pedersen

### Details

Date: Friday 21 Mar

Time: 14:00

Place: Aud. A

×
• ### Discovery-HET Seminar

Auditorium A, Thursday 27 Mar at 14:15

### Gavin Salam (CERN, Paris LPTHE)

Towards an understanding of jet substructure

# Discovery-HET Seminar

## Towards an understanding of jet substructure

### Abstract:

Jet substructure has proven itself to be an important tool to probe new physics at high scales at the LHC. It is likely to become even more essential in forthcoming LHC running at 13-14 TeV. However, jet substructure approaches suffer from the drawback that they are rather complicated, making it difficult to obtain insight and reliable calculations of their behaviour.
This talk will describe progress towards understanding three key jet substructure tools, using analytical QCD methods and will show how this progress is leading to improvements in jet substructure approaches.

### Details

Date: Thursday 27 Mar

Time: 14:15

Place: Auditorium A

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• April 2014
• ### Discovery-HET Seminar

Auditorium A, Tuesday 1 Apr at 14:15

### Lisa Glaser (NBI)

Causal sets: Discrete, non-local quantum gravity

# Discovery-HET Seminar

## Causal sets: Discrete, non-local quantum gravity

### Abstract:

The causal set programme is an approach to finding a theory of quantum gravity. It replaces the differentiable manifold of general relativity with a discrete partially ordered set. In this way it is possible to discretise space-time while retaining Lorentzian invariance. The downside is that this discretisation introduces non-local effects into the theory. In this talk I will give an introduction into causal set theory and talk about these non-local effects and first attempts to reconstruct locality.

### Details

Date: Tuesday 1 Apr

Time: 14:15

Place: Auditorium A

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• ### Discovery-HET Seminar

Auditorium A, Wednesday 2 Apr at 13:15

### Astrid Eichhorn (Perimeter)

Renormalization Group steps on the way to quantum gravity

# Discovery-HET Seminar

## Renormalization Group steps on the way to quantum gravity

### Abstract:

I will discuss the Renormalization Group as a useful tool in different quantum gravity models: On the one hand, the Renormalization Group can be used to investigate asymptotically safe quantum gravity. I will review the status of this scenario, and then explain how the coupling to matter gives us a way to test it: Too many dynamical matter degrees of freedom can destroy the Renormalization Group fixed point underlying asymptotic safety. Testing beyond-Standard-Model scenarios at the LHC, and discovering new particles could therefore potentially rule out asymptotically safe gravity. In the second part of this talk I will explain how the Renormalization Group can be used in discrete approaches to quantum gravity, such as matrix and tensor models, where it provides a way to search for the continuum limit.

### Details

Date: Wednesday 2 Apr

Time: 13:15

Place: Auditorium A

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• ### Discovery-HET Seminar

Aud A, Thursday 3 Apr at 14:15

### Walter Winter (DESY Zeuthen)

Perspectives for neutrino oscillations

# Discovery-HET Seminar

## Perspectives for neutrino oscillations

### Abstract:

The determination of the neutrino mass hierarchy and the leptonic Dirac CP phase are the outstanding issues in neutrino oscillation physics after the discovery of a non-zero value of theta_13. For the mass hierarchy, novel concepts have been recently drawing quite some attention. One example is a potential upgrade of the IceCube detector at the South Pole using the Earth matter effects on atmospheric neutrinos, called "Precision IceCube Next Generation Upgrade" (PINGU). For CP violation, most likely a dedicated long-baseline experiment will be needed. We discuss the prospects and challenges of these approaches, and the perspectives for neutrino oscillations in the coming years.

### Details

Date: Thursday 3 Apr

Time: 14:15

Place: Aud A

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• ### NBIA Colloquium

Auditorium A, Friday 4 Apr at 14:15

### Kim Sneppen

How can biodiversity be maintained?

# NBIA Colloquium

## How can biodiversity be maintained?

### Abstract:

A central problem in ecology is to identify mechanisms that maintain biodiversity, and I shall approach it from the viewpoint of mathematical models. Simple models with "predator-prey" interactions are unsatisfactory but it is possible to obtain much larger diversity with models with cyclic interactions inspired by the children's game of "rock-scissors-paper". I shall use communities of lichen on rock surfaces as a inspiration to discuss a new class of ecosystem models, in which diversity emerges when the likelihood of interactions falls below a certain critical threshold of 5.5%. The model emphasizes transient cyclic interactions as a key to creation of self organized ecological niches. In turn, these niches open up the possibility of subsequent speciation and dynamically sustained diversity.

### Details

Date: Friday 4 Apr

Time: 14:15

Place: Auditorium A

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• ### Discovery-HET Seminar

Auditorium A, Tuesday 8 Apr at 14:15

### Linda Carpenter (Ohio State University)

Collider Searches for Dark Matter in the Mono-Everything Search Channels

# Discovery-HET Seminar

## Collider Searches for Dark Matter in the Mono-Everything Search Channels

### Abstract:

Searches for dark matter at colliders typically involve signatures with energetic initial-state radiation without visible recoil particles. Searches for mono-jet or mono-photon signatures have yielded powerful constraints on dark matter interactions with Standard Model particles. I extend this to the mono-Z, W, and Higgs signatures and reinterpret ATLAS analyses of events with missing transverse momentum to derive constraints on the dark matter interaction mass scale and nucleon cross sections. Dark matter models are explored in the context of effective field theories describing interacts via weak scale mediator particles, and are compared to existing space-based searches for DM scenarios.

### Details

Date: Tuesday 8 Apr

Time: 14:15

Place: Auditorium A

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• ### Discovery-HET Seminar

Auditorium A, Thursday 10 Apr at 14:15

### Jacob Bourjaily (Harvard)

Scattering Amplitudes and the Positive Grassmannian

# Discovery-HET Seminar

## Scattering Amplitudes and the Positive Grassmannian

### Abstract:

In the past ten years, the study of scattering amplitudes in quantum field theory has led to a revolutionary reformulation of the subject. This revolution began with the discovery, in 2005, of a recursive expansion for scattering amplitudes (to leading order) in terms of planar, trivalent, two-colored graphs---called "on-shell diagrams." Around the same time that these diagrams were first drawn by physicists, they also started to appear in the mathematical literature (for entirely independent reasons) in the context of what is known as the "positroid stratification" of Grassmannian manifolds. Recently, these two independent lines of research came together, leading to many valuable insights on both sides. In my talk, I will outline the physical ideas behind these developments, and explain the many deep connections which have been found between scattering amplitudes and the geometry and combinatorics of the positroid stratification of the Grassmannian.

### Details

Date: Thursday 10 Apr

Time: 14:15

Place: Auditorium A

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• ### Discovery-HET Seminar

Auditorium A, Tuesday 22 Apr at 14:15

### Diederik Roest (Groningen)

Inflationary attractors in cosmology

# Discovery-HET Seminar

## Inflationary attractors in cosmology

### Abstract:

The framework of inflation has recently received spectacular observational support by the Planck and BICEP2 results. We will discuss the inflationary motivations and implications at a pedagogical level. In particular, we will focus on generic predictions of inflation and the role of universality and attractors in this framework.

### Details

Date: Tuesday 22 Apr

Time: 14:15

Place: Auditorium A

×
• ### HET journal club lunch

Fb-6, Wednesday 23 Apr at 12:30

# HET journal club lunch

### Details

Date: Wednesday 23 Apr

Time: 12:30

Place: Fb-6

×
• ### Discovery-HET Seminar

Auditorium A, Tuesday 29 Apr at 14:15

### Anatoly Dymarsky (MIT)

Scale and Conformal Invariance in QFT

# Discovery-HET Seminar

## Scale and Conformal Invariance in QFT

### Abstract:

It is usually taken for granted that a unitary Lorentz-invariant quantum field theory without dimensionful parameters (i.e. scale invariant QFT) is conformal. In two dimensions there is indeed a proof, but so far little was known about other dimensions. I will discuss recent progress establishing conformal symmetry of scale invariant QFTs in four and potentially six dimensions.

### Details

Date: Tuesday 29 Apr

Time: 14:15

Place: Auditorium A

×
• ### HET journal club seminar

Fb-6, Wednesday 30 Apr at 13:15

### Blai Garolera (Barcelona)

Applied localization: Everything you always wanted to know about Wilson loops but were afraid to ask

# HET journal club seminar

## Applied localization: Everything you always wanted to know about Wilson loops but were afraid to ask

### Abstract:

In this talk I will discuss some of the many applications, properties and undeniable beauty of Wilson loop operators in gauge theories, concentrating specially in superconformal quantum field theories. The main tools I will be using are the AdS/CFT correspondence and the localization technique of Witten and Pestun.

### Details

Date: Wednesday 30 Apr

Time: 13:15

Place: Fb-6

×
• May 2014
• ### MSc midterm colloquium

Fb6, Tuesday 6 May at 11:15

An overview of black branes

# MSc midterm colloquium

## An overview of black branes

### Abstract:

Black branes in string theory are believed to shed important light on the quantum structure of black holes. In recent years the study of black branes has grown steadily. I will present an overview of charged black p-brane solutions in string theory as well as discuss the blackfold approach to the dynamics of black branes embedded in a background space-time.

### Details

Date: Tuesday 6 May

Time: 11:15

Place: Fb6

×
• ### HET journal club lunch

Fb-6, Wednesday 7 May at 12:30

# HET journal club lunch

### Details

Date: Wednesday 7 May

Time: 12:30

Place: Fb-6

×
• ### MSc midterm colloquium

Fb6, Thursday 8 May at 11:15

### Isak Buhl-Mortensen

Conjecturing a dual CFT description of extremal Kerr

# MSc midterm colloquium

## Conjecturing a dual CFT description of extremal Kerr

### Abstract:

The evidence for an extremal Kerr/CFT is apparent in "The Kerr/CFT Correspondence" written by Monica Guica, Thomas Hartman, Wei Song, and Andrew Strominger. They conjecture that extremal Kerr black holes are holographically dual to a chiral two-dimensional CFT with central charge given by the angular momentum. The conjecture is based on the existence of consistent boundary conditions for NHEK, who's asymptotic symmetry group is found to form a copy of the Virasoro algebra and hence a central charge. Furthermore the temperature to be associated with the dual CFT is found. The temperature and central charge give a microscopic entropy as prescribed by Cardy's formula, which is found to coincide with the Bekkenstein Hawking entropy, i.e a quarter of the horizon area. These steps that take us from extremal Kerr to a CFT description are summarized in this talk.

### Details

Date: Thursday 8 May

Time: 11:15

Place: Fb6

×
• ### Discovery-HET Seminar

Aud A, Thursday 8 May at 14:15

### Anosh Joseph

Supersymmetric Yang-Mills Theories on the Lattice

# Discovery-HET Seminar

## Supersymmetric Yang-Mills Theories on the Lattice

### Abstract:

Certain classes of supersymmetric gauge theories, including the well known N=4 super Yang-Mills, can be formulated on a spacetime lattice preserving exact supersymmetry. I will describe the lattice formulations of several of these theories with four, eight and sixteen supercharges with and without matter. Having a definition of supersymmetric gauge theories on the lattice would provide a window into their non-perturbative regimes. I will also briefly describe the Monte Carlo techniques used to probe these theories at strong coupling.

### Details

Date: Thursday 8 May

Time: 14:15

Place: Aud A

×
• ### NBIA Colloquium

Auditorium A, Blegdamsvej 17, Friday 9 May at 14:15

### Peter Latham (University College London)

Neuroscience from a physicist's perspective

# NBIA Colloquium

## Neuroscience from a physicist's perspective

### Abstract:

The brain is arguably the most complicated object we have ever
studied. So complicated, in fact, that it isn't even clear what it is
we want to know about it. Here I'll try to settle on a specific set of
problems faced by both the neuroscientist studying the brain and the
brain itself, provide a sense of how hard they are, and point the way
toward possible solutions. Along the way I'll provide background into
what we know about the brain, and why standard physics approaches
might not work so well. I'll end on an optimistic note, though:
physicists do have much to contribute to neuroscience.

### Details

Date: Friday 9 May

Time: 14:15

Place: Auditorium A, Blegdamsvej 17

×
• ### HET journal club seminar

Fb-6, Wednesday 14 May at 13:15

### Stefano Mori (Parma)

Wilson loops on Hopf fibrations in N = 4 AdS/CFT

# HET journal club seminar

## Wilson loops on Hopf fibrations in N = 4 AdS/CFT

### Abstract:

We study the correlator of Wilson loops in N = 4 SYM in the particular setup of Hopf fibers. Depending on the angular separation between the fibers and the ratio of the radii of the 2-sphere where the fibers lie different phases appear. On the string theory side of AdS/CFT conjecture, connected solutions only exist when the loops are close to one another. Taking the loops far apart, a first order phase transition take place, the disconnected solution becoming dominant. In the particular limit of coplanar circles, we find perfect agreement with known results by Gross and Ooguri. Our solution is a generalization and allow to interpolate between BPS and non-BPS configurations, possibly shedding light on the supersymmetry structure of the correlators. The system can be thought as a deformation of the ordinary antiparallel lines giving the static quark-antiquark potential, that is correctly reproduced as the fibers approach one another.

### Details

Date: Wednesday 14 May

Time: 13:15

Place: Fb-6

×
• ### Discovery-HET Seminar

Aud A, Thursday 15 May at 14:30

### Marius de Leeuw

Yangian symmetry and deformed amplitudes

# Discovery-HET Seminar

## Yangian symmetry and deformed amplitudes

### Abstract:

In this talk I will discuss the recent R-operator approach to scattering amplitudes in N=4 SYM. This approach makes use of Yangian symmetry to construct the invariants of which scattering amplitudes are comprised. A different way of describing these Yangian invariants is via on-shell diagrams and we will discuss the map between the two formalisms. We will discuss tree-level amplitudes in detail and show that they can be classified by permutations. In the end I will briefly touch upon loops.

### Details

Date: Thursday 15 May

Time: 14:30

Place: Aud A

×
• ### PhD Defense

Aud. A, Monday 19 May at 14:15

### Ara Martirosyan

Holographic three-point functions

# PhD Defense

## Holographic three-point functions

### Abstract:

The main subject of this thesis is the computation of structure constants
appearing in the three-point functions for certain type of
states/operators in the context of the AdS/CFT correspondence, which is
one of the important parts of the dynamical problem in the dual theories
of the correspondence. In the spirit of understanding this problem better,
the thesis discusses the divergences appearing in the calculation of
structure constants involving two giant and one point-like gravitons in
backgrounds.

Coherent state approach for the tree-level calculation of structure
constants for heavy-heavy-light operators in the SU(2) x SU(2)
sector of the ABJM theory is carried out both on weak and strong coupling
sides of the theory.

Another remarkable determinant-result is obtained in the same sector of
ABJM theory using integrability techniques for operators with precise
anomalous dimensions.

### Details

Date: Monday 19 May

Time: 14:15

Place: Aud. A

×
• ### Discovery-HET Seminar

Aud A, Tuesday 20 May at 14:15

### Andrzej Wereszczynski

Three point functions and the moduli averaging

# Discovery-HET Seminar

## Three point functions and the moduli averaging

### Abstract:

I will show that the conventional method to calculate the OPE coefficients in the strong coupling limit for heavy-heavy-light operators in the N=4 SYM has to be modified by integrating the light vertex operator over the moduli space of classical solutions corresponding to the heavy states. This proposal will be tested in three examples: the BMN vacuum correlator, for folded strings on $S^5$ and for two-particle states.

### Details

Date: Tuesday 20 May

Time: 14:15

Place: Aud A

×
• ### HET journal club seminar

Fb-6, Wednesday 21 May at 13:15

### Didina Serban (Saclay)

Three point function in N=4 SYM at weak coupling

# HET journal club seminar

## Three point function in N=4 SYM at weak coupling

### Details

Date: Wednesday 21 May

Time: 13:15

Place: Fb-6

×
• ### Discovery-HET Seminar

Auditorium A, Tuesday 27 May at 14:15

### Aalok Misra (Indian Institute of Technology)

Local MQGP Dynamics

# Discovery-HET Seminar

## Local MQGP Dynamics

### Abstract:

I first discuss a string theory construct relevant to the study of thermal QCD-like theories, used in the literature. I then discuss its uplift/oxidation, locally, from an M-theoretic/D=11 supergravity perspective. In the process, I discuss results related to demonstrating thermodynamical stability of the construct/uplift, shear viscosity - entropy density ratio, diffusion constant (D), electrical conductivity(sigma), charge susceptibility (chi) [thereby Einstein's relation D=sigma/chi] from supergravity solutions as well two-point
functions involving gauge field and metric fluctuations.

### Details

Date: Tuesday 27 May

Time: 14:15

Place: Auditorium A

×
• June 2014
• ### Discovery-HET Seminar

Auditorium A, Blegdamsvej 17, Tuesday 3 Jun at 14:15

### James Drummond

Bootstrapping scattering amplitudes in N=4 super Yang-Mills theory

# Discovery-HET Seminar

## Bootstrapping scattering amplitudes in N=4 super Yang-Mills theory

### Abstract:

I will describe the relevant class of analytic functions for describing the perturbation expansion of the six-particle amplitudes in N=4 super Yang-Mills theory. I will show how imposing physical consistency conditions based on collinear behaviour or high-energy Regge behaviour allows us to determine the MHV amplitude up to four loops without first obtaining any loop integrand.

### Details

Date: Tuesday 3 Jun

Time: 14:15

Place: Auditorium A, Blegdamsvej 17

×
• ### HET journal club seminar

Fb-6, Wednesday 4 Jun at 13:15

### Jørgen Rasmussen (University of Queensland)

Constructive fun with doodles: from diagram algebras to exact solutions

# HET journal club seminar

## Constructive fun with doodles: from diagram algebras to exact solutions

### Abstract:

An informal introduction to loop models is presented. These models have become fundamental tools in the description of physical systems with nonlocal degrees of freedom such as polymers and percolation. Their basic degrees of freedom are encoded in connectivities and are thus topological in nature. As intimidating as this may sound, underlying diagram algebras offer unlimited doodling fun for the whole family and can be used to establish integrability of the associated physical models. Critical dense polymers, in particular, can subsequently be solved exactly in a way rivalled only by the Ising model.

### Details

Date: Wednesday 4 Jun

Time: 13:15

Place: Fb-6

×
• ### Discovery-HET Seminar

Auditorium A, Tuesday 10 Jun at 14:15

### Sinya Aoki

Nuclear forces from quarks and gluons

# Discovery-HET Seminar

## Nuclear forces from quarks and gluons

### Abstract:

In this talk, I will introduce our recent attempt to derive the nuclear forces from quarks and gluons using numerical simulations in lattice QCD. I will first explain the strategy for how to extract potentials in quantum field theories in detail. I then employ our method to derive the nucleon-nucleon potential in lattice QCD. Finally, I will discuss recent progress in the method as applied to systems such as hyperon-nucleon, hyperon-hyperon, meson-baryon and three nucleons.

### Details

Date: Tuesday 10 Jun

Time: 14:15

Place: Auditorium A

×
• ### HET journal club seminar

Fb-6, Wednesday 11 Jun at 13:15

# HET journal club seminar

### Abstract:

In this talk, I will introduce a map between Einstein spaces of positive and negative curvature. Starting from a space of positive curvature with some dimensions compactified on a sphere and analytically continuing the number of compact dimensions, we obtain a space of negative curvature with a compact hyperbolic subspace, and vice versa. I will show some applications of such map as mapping pure de Sitter and Anti-de Sitter space, as well as black hole spacetimes with (A)dS asymptotics and perturbed versions thereof. Finally, I will conclude with a remarkable result useful for holography in dS space: the boundary of asymptotically AdS spaces is mapped to a brane in the bulk of de Sitter, and perturbations near the AdS boundary are sourced by a stress tensor confined to this brane.

### Details

Date: Wednesday 11 Jun

Time: 13:15

Place: Fb-6

×
• ### Discovery-HET Seminar

Auditorium A, Thursday 12 Jun at 14:15

### Joachim Kopp (Heidelberg)

Flavor Violating Higgs Decays

# Discovery-HET Seminar

## Flavor Violating Higgs Decays

### Details

Date: Thursday 12 Jun

Time: 14:15

Place: Auditorium A

×
• ### HET journal club lunch

Fb-6, Wednesday 18 Jun at 12:30

# HET journal club lunch

### Details

Date: Wednesday 18 Jun

Time: 12:30

Place: Fb-6

×
• ### Discovery-HET Seminar

Aud. M, Thursday 19 Jun at 14:15

### Ori Ganor (Berkeley)

"Chern-Simons theory, S-duality, and a Tridiagonal Determinant Identity."

# Discovery-HET Seminar

## "Chern-Simons theory, S-duality, and a Tridiagonal Determinant Identity."

### Abstract:

An equivalence between two Hilbert spaces will be developed: (i) the space of states of $U(1)^n$ Chern-Simons theory on $T^2$ with coupling constants given by a certain class of tridiagonal matrices (with corners); and (ii) the space of ground states of strings on an associated mapping torus with $T^2$ fiber. The equality of dimensions of the two Hilbert spaces (i) and (ii) is equivalent to a known identity on determinants of tridiagonal matrices with corners. The equivalence of operator algebras acting on the two Hilbert spaces follows from a relation between the Smith normal form of the Chern-Simons coupling constant matrix and the isometry group of the mapping torus, as well as the torsion part of its first homology group. The equivalence follows by studying the space of ground states of SL(2,Z)-twisted circle compactifications of U(1) gauge theory, connected with a Janus configuration, and further compactified on a torus. Extension to U(n) gauge theory will also be discussed.

### Details

Date: Thursday 19 Jun

Time: 14:15

Place: Aud. M

×
• ### HET journal club seminar

Fb-6, Wednesday 25 Jun at 13:15

### Charlotte Kristjansen (NBI)

A certain probe D-brane model and its possible relevance for graphene

# HET journal club seminar

## A certain probe D-brane model and its possible relevance for graphene

### Details

Date: Wednesday 25 Jun

Time: 13:15

Place: Fb-6

×
• July 2014
• ### HET journal club seminar

Fb-6, Tuesday 1 Jul at 14:15

### Costas Zoubos (University of Pretoria)

Marginal deformations and non-integrability

# HET journal club seminar

## Marginal deformations and non-integrability

### Details

Date: Tuesday 1 Jul

Time: 14:15

Place: Fb-6