High Energy Theory Seminars and Theory Colloquia.

These seminars take place every Wednesday at 15:00 in Room S.

High Energy Theory seminars are organized by M. Passera and C. Hagedorn (PH) and G. Dall'Agata and D. Cassani (TH). They are one-hour research seminars dedicated to high energy physics, cosmology and astrophysics, with a special emphasis on particle physics (PH, light gray) and string theory (TH, dark gray).

Theory Colloquia are organized by G. Dall'Agata and M. Passera. They are one hour seminars devoted to reviews of hot topics in high energy physics.
They appear in the following list marked in light yellow.

Sometimes we also host some special events, like workshops and conferences. These are highlighted in light blue.

You can click on the titles to see the slides of the talk.


2011/2012 Calendar   



Date Speaker
(Affiliation)
Title Room
&Time
05-09-11
Monday
PD Strings 2011 (05/09-09/09)
PadovaBo
9:00
13-09-11
Tuesday
Nobuhiro Maekawa
Nagoya Univ.
E6 GUT and spontaneous CP violationAula S
15:00
27-09-11
Tuesday
B.D.Callen
Uni Melbourne
Domain-Wall Braneworld Models and Supersymmetry
Abstract
We study an SU(5) 4+1d domain-wall braneworld model employing the Dvali-Shifman mechanism to trap Standard Model gauge fields on the wall. We discuss the background domain wall configuration, field localisation, and the phenomenology of the SM fermions in the model, in particular fermion mass textures. We also discuss the possible realisation of a supersymmetric version of such a model.
Aula S
15:00
11-10-11
Tuesday
J.R. Espinosa
ICREA, Barcelona
Implications of the Latest LHC Data for a Composite Higgs
Abstract
One of the main tasks of the LHC is the experimental scrutiny of the mechanism behind electroweak symmetry breaking. In particular, we want to learn whether such mechanism is perturbative and employs an elementary Higgs boson (as in Supersymmetry) or strongly coupled and leads to a composite Higgs (these two being the most serious alternatives). In this talk I examine composite Higgs models, in which the Higgs emerges as a pseudo-Goldstone boson from a strongly-interacting sector. The properties of such Higgs deviate from its SM properties and I discuss how this affects the sensitivity of LHC Higgs searches and the implications of the latest LHC results for such scenarios.
Aula S
16:30
19-10-11
Wednesday
D.Anselmi
Pisa Uni.
Scalarless Standard Model with high-energy Lorentz violation
Abstract
I discuss an extension of the Standard Model that violates Lorentz symmetry at high energies. The model is renormalizable, contains four fermion interactions at the fundamental level and has no elementary scalar. A Nambu-Jona-Lasinio mechanism give masses to fermions and gauge bosons and generates composite Higgs fields at low energies. I show that there exists a domain in parameter space where the low-energy effective theory is compatible with data, within theoretical errors. Relations among the parameters of the Standard Model are predicted. I also argue that a scale of Lorentz violation smaller than the Planck scale is compatible with data (assuming that CPT symmetry is preserved).
Aula S
15:00
25-10-11
Tuesday
Chee Sheng Fong
INFN Frascati
Baryogenesis (Leptogenesis) from Soft supersymmetry Breaking
Abstract
If supersymmetry (SUSY) is realized in nature, it has to be broken and the existence of the soft SUSY-breaking terms introduce additional CP-violating sources which can be utilized in leptogenesis in a scenario termed Soft Leptogenesis (SL). First, we study the CP violation in SL and show that for all soft SUSY-breaking sources of CP violation an exact cancellation between the leading order asymmetries produced in the fermionic and bosonic channels occurs at T=0. Hence thermal effects have to be taken into account to partially lift this cancellation. Then we discuss the effective theory appropriate for studying SL. In the temperature range relevant for SL lepton flavor effects play an important role and in particular they could enhance the efficiency of SL by up to a factor of 1000 from the unflavored scenario, permitting larger values of the required lepton-number-violating soft bilinear term up to a natural SUSY scale (TeV). Interestingly at temperatures T > 10^7 GeV the main source of B-L asymmetry is the CP asymmetry of a new anomalous R-charge. This results in baryogenesis through R-genesis with an efficiency that can be up to two orders of magnitude larger than in the usual estimates. Contrary to common belief, in this regime, a sizeable baryon asymmetry is generated also when thermal effects are neglected.
Aula S
15:00
09-11-11
Wednesday
S.El-Showk
CEA Saclay
Emergent Spacetime and Holographics CFTs
Abstract
We discuss universal properties of conformal field theories with holographic duals. A central feature of these theories is the existence of a low-lying sector of operators whose correlators factorize. We demonstrate that factorization can only hold in the large central charge limit. Using conformal invariance and factorization we argue that these operators are naturally represented as fields in AdS as this makes the underlying linearity of the system manifest. In this class of CFTs the solution of the conformal bootstrap conditions can be naturally organized in structures which coincide with Witten diagrams in the bulk. The large value of the central charge suggests that the theory must include a large number of new operators not captured by the factorized sector. Consequently we may think of the AdS hologram as an effective representation of a small sector of the CFT, which is embedded inside a much larger Hilbert space corresponding to the black hole microstates.
Aula S
15:00
16-11-11
Wednesday
Steve Blanchet
EPFL-Lausanne
Flavored Dark Matter, and Its Implications for Direct Detection and Colliders
Abstract
I will discuss theories where the dark matter particle carries flavor quantum numbers, and has renormalizable contact interactions with the Standard Model fields. The phenomenology of this scenario depends sensitively on whether dark matter carries lepton flavor, quark flavor or its own internal flavor quantum numbers. I will theoretically motivate each of these cases, and show that they are associated with characteristic couplings and mass spectra in order to evade present bounds. Imposing dark matter to be a thermal relic, we find that the allowed parameter space is in general within reach of current direct detection experiments. For the collider phenomenology, I will focus on a class of models where dark matter carries tau flavor, and show that the collider signals of these models include events with four or more isolated leptons and missing energy. Such models can be discovered at the 14 TeV LHC, and flavor and charge correlations among final state leptons may allow them to be distinguished from unflavored DM models.
Aula S
15:00
23-11-11
Wednesday
Marco Nardecchia
CP3-Origins, Odense
Flavor Violation without R-parity and Neutrino Masses
Abstract
The Minimal Supersymmetric Standard Model (MSSM) has become over the years the principal extension of the Standard Model. Interestingly, if we allow for a small amount of R-parity violation, the MSSM can also provide neutrino masses and mixing without the need of extra states. In this context, introducing a symmetry principle, we are able to link the phenomenology of flavor changing in the charged lepton sector to neutrino masses and mixing angles.
Aula S
15:00
30-11-11
Wednesday
Anna Kaminska
Uni Warsaw
If no Higgs then what?
Abstract
In the absence of a Higgs boson the perturbative description of the Standard Model breaks down at energies around 1 TeV. Heavy spin-1 fields coupled to W and Z bosons can extend the validity of the theory up to higher scales. In my talk I will discuss the prospects to observe the degrees of freedom that unitarize the WW scattering amplitudes in the context of strong electroweak symmetry breaking saturated by vector resonances. The study performed in a simple self-consistent setup with a well defined range of validity will enable us to answer the question about the allowed mass range for the lightest set of resonances. A "nightmare" scenario, with no Higgs nor resonances within the LHC reach, will be mentioned.
Aula S
15:00
07-12-11
Wednesday
Duccio Pappadopulo
EPFL-Lausanne
On the effect of resonances in composite Higgs phenomenology
Abstract
A generic composite Higgs model based on the SO(5)/SO(4) coset is considered and the prospects for the LHC and the future linear colliders to detect the least model dependent signatures of such scenario are discussed. In order to go beyond the leading low-energy approximation and to introduce in a controlled way the lowest-lying resonances that may exist in the model, the criterion of 'partial UV completion' is defined. I then discuss the impact of the new states on the signals associated with high-energy vector boson scattering and explain the correlation between the quantum numbers of the resonances and the characteristic pattern of enhancement or depletion of the signal in the various isospin channels.
Aula S
15:00
14-12-11
Wednesday
Miguel Pato
TU Munich
Pinpointing the dark matter distribution in the Milky Way: microlensing and dynamical constraints
Abstract
Direct dark matter searches have prompted a lot of excitement in recent years, mainly due to a combination of startling signals and null results. After briefly reviewing the status of direct dark matter searches, I will motivate the need for a more accurate description of the dark matter distribution in our Galaxy. In this context, I will show that gravitational microlensing and dynamical observables can be combined to set interesting constraints on the dark matter local density and profile slope. The most commonly discussed dark matter profiles are found compatible with microlensing and dynamical observations, while the local dark matter density is constrained to be in the range 0.20-0.56 GeV/cm^3. Future directions will be discussed.
Aula S
15:00
11-01-12
Wednesday
L. Ubaldi
Uni Bonn
Probing dark matter with cosmic rays and AGN jets
Abstract
We consider a new possible signature of dark matter in the spectrum of gamma-ray photons resulting from the scattering of high-energy particles off of dark matter particles. We study this scattering process in two different contexts: Active Galactic Nuclei (AGN) and our own galaxy. In the former, high-energy electrons and protons are provided by the AGN jets, while in the latter they are provided by cosmic rays. We show that in specific dark matter models the cross section is enhanced by resonances that could lead to a potentially detectable feature in the gamma-ray spectrum.
Aula S
15:00
18-01-12
Wednesday
M. Porrati
NYU
Surprises with Interacting High Spin Particles
Abstract
This colloquium reviews old and new no go theorems that severely constrain possible interactions of massless high spin particles. Massive particles can interact with gauge fields and gravity, but often they are plagued by pathologies such as superluminal propagation in nontrivial backgrounds. The last part of the talk uses the example of open string theory to show that such pathologies can be avoided by an appropriate choice of non-minimal interactions.
Aula S
15:00
25-01-12
Wednesday
G. L. Cardoso
Universidade Tecnica de Lisboa
Nernst branes in gauged supergravity
Abstract
We study static black brane solutions in the context of N = 2 gauged supergravity in four and five dimensions. Using the formmalism of first-order flow equations, we construct novel extremal black brane solutions including examples of Nernst branes, i.e. extremal black brane solutions with vanishing entropy density.
Aula S
15:00
15-02-12
Wednesday
Alessandro Vicini
Milano U.
Higgs production at hadron colliders in the POWHEG approach in the SM and in the MSSM
Abstract
In this talk I will review the status of Higgs searches at hadron colliders, focusing on some aspects of the theoretical predictions. The gluon fusion mechanism plays a key role in Higgs phenomenology at hadron colliders and requires the best possible accuracy in the prediction of the total and of the differential cross sections. I will present a new implementation of this process in the SM and in the MSSM, in the POWHEG approach, with NLO accuracy and including the effects of multiple gluon emission via a QCD parton shower. Phenomenological results in the SM and in the MSSM illustrate which observables can help to discriminate between the two models.
Aula S
15:00
22-02-12
Wednesday
Diego Marques
CEA Saclay
Gauged Double Field Theory
Abstract
I will begin with a motivation and introduction to Double Field Theory (DFT), and put special emphasis in discussing its gauge symmetries and the constraints derived from them. I will then show that the constraints admit a class of solutions for which the theory is effectively described by a lower dimensional Gauged DFT. The gaugings in the effective theory are obtained from duality twists, and the constraints force them to satisfy Jacobi-like quadratic constraints. The action, symmetries, bracket and constraints are derived by twisting their analogs in the parent higher dimensional DFT. Finally, I will discuss the embedding of gauged supergravities and heterotic supergravities in Gauged DFT.
Aula S
15:00
28-02-12
Tuesday
Sergio Ferrara
CERN
Electric Magnetic Duality and Groups of Type E7Aula S
16:00
29-02-12
Wednesday
Claudio Scrucca
EPFL
Sequestered supersymmetry breaking and its realization in string models
Abstract
In this talk, I will start by reviewing the general idea of sequestered supersymmetry breaking and its generalization involving some global symmetry, and explain how this may naturally lead to approximately universal soft scalar masses. I will then report on a study of the possibility of realizing this mechanism in generic Calabi-Yau string models, focusing on heterotic models with supersymmetry breaking occurring in the Kahler moduli and matter field sectors. I will first outline how the contact terms in the effective Kahler potential that are potentially relevant for soft scalar masses can be computed, and describe what is their geometric interpretation, emphasizing the differences with the simpler case of toroidal orbifolds. I will then discuss under which conditions there exist suitable global symmetries that could be imposed to the unknown effective superpotential in such a way to ensure the vanishing of the corresponding unwanted tree-level contribution to soft scalar masses.
Aula S
15:00
14-03-12
Wednesday
Hristov, K.
Utrecht U.
A superalgebra perspective on four dimensional black holes
Abstract
This talk aims at emphasizing the role of superalgebras for the understanding of black hole physics. I first outline a general method for the derivation of supercharges, based on the Noether theorem. This method is then applied in the context of D=4 N=2 supergravity, where Minkowski and AdS vacua are analyzed. This allows us to define precisely the conserved charges of asymptotically flat and AdS black holes and note the differences between their near-horizon geometries. In the end, a superalgebra argument is presented to explain the absence of static electric BPS black holes in AdS in a wide class of theories.
Aula S
15:00
21-03-12
Wednesday
Jernej F. Kamenik
J. Stefan Institute & Uni Ljubljana
CP Violation in Charm
Abstract
The LHCb collaboration recently announced preliminary evidence for CP violation in D meson decays. I will discuss this result in the context of the standard model, as well as its extensions. Within the effective theory framework I will investigate constraints on the relevant operators from other processes. In particular I will show that the bound from epsilon'/epsilon prohibits purely left-handed SU(3)Q flavor symmetry breaking explanations. On the other hand, chiral symmetry (left-right flavor) breaking contributions are natural candidates to explain this effect, via enhanced chromomagnetic operators. Implications for supersymmetric and warped extra-dimensional models will be briefly discussed.
Aula R
16:00
28-03-12
Wednesday
Thomas Van Riet
CEA Saclay
The mysterious backreaction of anti-branes in warped throats
Abstract
In this talk I will overview and discuss the recent developments in understanding the backreaction of anti-branes in warped throats. Such branes form basic building blocks in de Sitter models and holographic models of non-supersymmetric confining gauge theories, within string theory. Recently it has been understood that such solutions have specific kind of singular fluxes and I will explain what the trouble is with these singularities.
Aula S
15:00
04-04-12
Wednesday
Sergey Sibiryakov
INR Moscow
Emergent Lorentz invariance: holographic description
Abstract
I wil explore the hypothesis that Lorentz invariance may appear as the property of the infrared fixed points of the RG flow in intrinsically non-relativistic theories. For this appearance to be effective, the theory must be strongly coupled. I will present a holographic description of this phenomenon and discuss, in which precise sense the Lorentz invariance emerges.
Aula S
14:00
18-04-12
Wednesday
M. Perez-Victoria
Uni Granada & CAFPE
The top asymmetry across the sea
Abstract
The CDF and D0 collaborations have persistently measured an anomaly in the forward-backward asymmetry in top pair production at Tevatron. The different new physics models designed to account for this effect have consequences that can be tested at the LHC. I will discuss the implications of the recent Atlas and CMS results for these models.
Aula S
15:00
02-05-12
Wednesday
M. Neubert
Johannes Gutenberg Uni
Precision Higgs and flavor physics as indirect probes of a warped extra dimension
Abstract
Extensions of the Standard Model featuring a warped extra dimension are among the main competitors to Supersymmetry. These models, first proposed by Randall and Sundrum, address the gauge hierarchy problem and the flavor puzzle by means of the same geometrical mechanism. Precision measurements of rare flavor-changing processes and loop-induced production and decay rates of the Higgs boson provide sensitive indirect probes for physics beyond the Standard Model, which in many cases are sensitive to mass scales outside the reach for direct production at the LHC. I will discuss the status of Randall-Sundrum models and illustrate its implications for precision flavor and Higgs physics.
Aula S
15:00
08-05-12
Tuesday
Yann Mambrini
LPT, Orsay
Dark matter, candidates, signals and LHC consequences
Abstract
Very recently several hints of Higgs or Dark Matter discoveries have been claimed: 125 GeV Higgs in ATLAS/CMS combined analysis, DAMA/CoGENT/CRESST excess in direct detection experiments of Dark Matter. In this seminar I will try to see if it is possible to conciliate the more recent astrophysical data with the most popular extensions of the Standard Model depending on the nature of the Dark Matter candidate. We will also look at the consequences of the Higgs searches on the mass and couplings of the Dark Matter particle to the Higgs sector and its perspective of discovery in a near future.
Aula R
16:30
09-05-12
Wednesday
Marco Serone
SISSA,ICTP,INFN Trieste
General 4D Composite Higgs Models
Abstract
We study genuinely four-dimensional models of a pseudo-Goldstone composite Higgs that are not of moose-type or related by deconstruction to five-dimensional models. We characterize the main properties these models should have in order to give rise to an Higgs mass at around 125 GeV. We focus on the minimal SO(5)/SO(4) coset, and assume the existence of relatively light and relatively weakly coupled vector and axial resonances, as well as fermion resonances that give mass to the SM fermions through the mechanism of partial compositeness. The Higgs potential is assumed to be one-loop dominated by the above resonances and by SM fields. In absence of a symmetry principle, the long distance one-loop potential is made calculable by suitable generalizations of the first and second Weinberg sum rules. We show that in minimal set-ups a 125 GeV Higgs requires light, often sub-TeV, fermion resonances. The composite Higgs models of the moose-type considered in the literature can also be seen as particular limits of our class of models.
Aula S
15:00
11-05-12
Friday
Thomas Schwetz
MPI-K Heidelberg
Sterile Neutrinos at the eV Scale?
Abstract
Since more than 10 years the LSND evidence for muon to electron antineutrino transitions motivates the hypothesis of sterile neutrinos at the eV scale. Additional hints in favour of this possibility are anomalies in calibration data of Gallium solar neutrino experiments and global data from reactor neutrino experiments in light of recent re-evaluations of neutrino fluxes from nuclear reactors. I give an overview of the current situation, arguing that at present no consistent picture has emerged yet and there is tension between data favouring and disfavouring sterile neutrinos at the eV scale.
Aula S
12:00
16-05-12
Wednesday
Federico Piazza
APC, Paris Center for Cosmological Physics
Spontaneous Symmetry Probing
Abstract
I will give account of two recent papers and ongoing projects in which the general implications of symmetries in the case of time-dependent field states are studied. In particular, I will be interested in field configurations that spontaneously "probe" the symmetry - or one of the symmetries - in the sense that they evolve in time along a symmetry direction in field space. This situation should capture certain essential features of generic early Universe inflationary models without committing too much with their microphysical details. The same formalism applies also to other - apparently disparate - situations, such as many-body systems at finite chemical potential.
Aula S
15:00
23-05-12
Wednesday
Emiliano Sefusatti
ICTP
Testing the initial conditions with the Large-Scale Structure of the Universe: The galaxy power spectrum, the bispectrum and the interesting case of Quasi-Single Field Inflation
Abstract
The possible detection of a non-Gaussian component in the initial condition of the Universe could provide crucial information on the physics of inflation. While current constraints on non-Gaussian parameters are still consistent with the Gaussian hypothesis, the Planck satellite will soon significantly improve these limits. In case of detection, a confirmation from different observables, as for instance the galaxy distribution, will be required. I will review the basic effects of non-Gaussian initial conditions on the evolution of the large-scale structure of the Universe, paying specific attention to how they affect the nonlinear growth, both of the matter power spectrum and higher-order correlation functions as well as the corrections induced to linear and nonlinear galaxy bias. In addition, I will present in detail the case of the Quasi-Single Field model of inflation, characterized by a quite rich phenomenology in terms of its observational consequences.
Aula S
15:00
28-05-12
Monday
PLANCK 2012 (28/05-01/06)
Warsaw
20-06-12
Wednesday
Erik Tonni
SISSA
Entanglement entropy: insights from the two intervals case
Abstract
While the entanglement entropy for one interval in two dimensional CFT is sensible only to the central charge, in the case of many intervals it includes the full operator content of the theory. We make this statement manifest through an OPE expansion valid for any CFT. This general result is tested quantitatively for the compactified boson and the Ising model, where the expressions of the Renyi entropies are derived in terms of Riemann theta functions. Such expressions are checked against numerical data obtained from spin chains. The holographic entanglement entropy for two disjoint intervals in the boundary theory is discussed, also for the time dependent backgrounds given by the Vaidya metrics, which model the black hole formation.
Aula S
15:00
05-07-12
Thursday
Olaf Kittel
Uni Granada
Heavy Neutrinos and Lepton Flavor Violation in Left-Right Symmetric Models at the LHC
Abstract
In the framework of left-right symmetric models, we discuss lepton flavor violation in the production and the decay of heavy right-handed neutrinos at the LHC. We determine the LHC sensitivity to test the right-handed neutrino mixing matrix, as well as the sensitivity on the masses of the right-handed gauge bosons and heavy neutrinos. We compare the LHC sensitivities with those from other lepton flavor violation (LFV) processes at low energy, to identify favorable areas of the parameter space to explore the complementarity between LFV at low and high energies.
Aula S
11:30