A brief overview of the ultra-relativistic heavy ion physics programme at the Large Hadron Collider at CERN will be given. Collisions of lead ions have been studied at a center-of-mass energy per nucleon of 2.76 TeV (run I), and, more recently, at 5.02 TeV (run II). The ultimate goal of heavy-ion collisions is the study of the properties of the deconfined and chirally restored state of matter...
I review recent results on QCD thermodynamics from lattice simulations. In particular, I will focus on the QCD equation of state at zero and finite chemical potential, the curvature of the phase diagram and fluctuations of conserved charges. The latter will be compared to experimental data, to the purpose of extracting the chemical freeze-out temperature and chemical potential from first principles.
Uncovering the nature of the electroweak (EW) phase transition in the early Universe would be key to shed light on the possible origin of the cosmic matter-antimatter asymmetry. We discuss various ways in which searches for new physics beyond the Standard model at the LHC can be used to probe the nature of the EW phase transition, and their implications for the generation of the baryon...
There has been a growing evidence that the standard formulation of Quantum Field Theory using path integrals and Feynman diagrams fails to explain unexpected simplicity and hidden symmetries of the scattering amplitudes. I show that in a certain gauge theory there exists a radically different picture for amplitudes as volumes of "Amplituhedron" which is a higher-dimensional generalization of...
There are good motivations to consider that the flavour structure could emerge during electroweak symmetry breaking, for example if the Froggatt-Nielsen field dynamics were linked to the Higgs field. Remarkably, the the nature of the electroweak phase transition is completely changed when the Standard Model Yukawas vary at the same time as the Higgs is acquiring its vacuum expectation value,...
Stability of the electroweak vacuum in the very early universe is a novel probe of high energy physics. A key question
is whether new physics beyond SM is required to maintain stability against inflationary fluctuations of the Higgs field.
Here curvature couplings induced by radiative corrections in curved space play a crucial role. I review the topic and show
that curvature effects can keep...
In order to investigate structure of Pb nuclei at high energies we study forward dijet production in p-Pb hadronic collisions.
We propose a framework for evaluating cross section for production of forward dijets that encompasses Color Glass Condensate and high energy factorization effects and is therefore applicable regardless of the magnitude of transversal momenta of produced jets.
The...
I will present the recent developments [JHEP05(2016)141] of the semi-holographic model first proposed in [JHEP06(2015)003]. The semi-holographic approach makes it possible to combine Color Glass Condensate initial conditions and weak-coupling glasma field equations with a simultaneous evolution of a strongly coupled infrared sector describing the soft gluons radiated by hard partons. The new...
We thoroughly investigated the applicability of the two-particle irreducible
(2PI) formalism in the description of phase transitions occurring at finite temperature in scalar field theories. We studied the importance of truncation effects on the order of the phase transition and indeed found that the long known problem of the Hartree-Fock truncation is cured by improving the approximation to...
We discuss the evolution of an energetic jet which propagates through a dense quark-gluon plasma
and radiates gluons due to its interactions with the medium. Within perturbative QCD,
this evolution can be described as a stochastic branching process, that we have managed to solve exactly.
We present exact, analytic, results for the gluon spectrum (the average gluon distribution)
and for...
Understanding the complicated field dynamics taking place in a heavy ion collision is a difficult task. Holography provides us with a framework that enables us to study the strongly coupled sector of certain gauge theories.
We mimic the heavy ion collision by two gravitational shock waves and monitor the time evolution of the dual strongly coupled super Yang-Mills plasma via non-local...
The dynamics of inhomogeneous quantum fields out of equilibrium are especially relevant for the study of first-order phase transitions. It is our aim to calculate how critical bubbles of the new phase -that form in such a process- propagate for different quantum field theories. The Electroweak phase transition in the early universe is of particular interest, since Baryogenesis can potentially...
Ever since fast hydrodynamization has been observed in heavy ion collisions the understanding of the very early non-equilbrium stage of such collisions has been a topic of intense research. We use the gauge/string duality to model the creation of a strongly coupled Quark-Gluon plasma in a non-conformal gauge theory. We focus on new physics (as compared to the conformal case) such as the...
The momentum distribution of quark-gluon plasma at the early stage of a relativistic heavy-ion collision is anisotropic and consequently the system, which is assumed to be weakly coupled, is unstable due to chromomagnetic plasma modes. We consider a high-energy parton which flies across such an unstable plasma, and the energy transfer between the parton and the medium is studied as an initial...
In the study of phase transitions in the early universe, methods based on $N$ particle irreducible effective actions have become very important for describing the out of equilibrium dynamics of these phenomena. Equations of motion for classical 1-, up to $N$-point functions can be obtained from stationarity conditions. However, in order to extract physical information, the action must first be...
Previous calculations have shown that the 2 particle irreducible (2pi) effective theory is a promising method to study strongly coupled systems, for which non-perturbative techniques are needed. Calculations at the 3 loop level show improved convergence, relative to perturbative results. We present results in \phi^4 theory at the 4 loop level which show that convergence breaks down at large...
We present the first analysis of event shape distributions in e+e- annihilation into a dijet pair in a high-temperature quark-gluon plasma in thermal equilibrium. We focus on temperatures much smaller than the jet mass, such that the jet function remains unresolved by medium fluctuations. In this limit, the medium influences the cross-section of the process only through the dijet soft function...
Holography provides a powerful tool for studying out-of-equilibrium strongly interacting quantum fields. Most works on this subject have focused on the dynamics of local operators, as for instance on how quickly they approach hydrodynamic behavior. We have developed the first general method for studying time-dependence of the causal response function in holography for arbitrary non-equilibrium...
We show that effective field theory techniques can be applied
in the high temperature T plasmas to
improve the accuracy of the physics of the hard scales ( or scales of order T).
At leading order in the
coupling constant the hard scales of the plasma can be viewed as
on-shell classical particles. Based on this observation, and without any
reference
to the state of the system, we...
Chirality of fermions has a topological nature. This microscopic property modifies the macroscopic hydrodynamic behavior and leads to unusual transport phenomena protected by topology in relativistic systems. We show how conventional kinetic theory should be modified to take into account such effects. We also discuss their potential importance in strong and electroweak matter, and, in...
I will summarize a recent estimation (arXiv:1605.07720) of the thermal masses and damping rates of active (m < eV) and sterile (M ∼ GeV)
neutrinos with thermal momenta k ∼ 3T at temperatures below the electroweak crossover
(5 GeV < T < 160 GeV). These quantities in turn fix the washout rates of Standard
Model lepton number densities and the thermal production rate of sterile neutrinos....
Surprisingly, unlike mesonic correlators, baryonic correlators at nonzero temperature have only been studied in a handful of studies. Here we present a lattice study of baryonic correlators and spectral functions across the deconfinement transition, using FASTSUM's 2+1 Wilson ensembles. We present results for in-medium effects below Tc and parity doubling above Tc.
High-energy particles passing through matter lose energy by showering via hard bremsstrahlung and pair production. At very high energy, the quantum duration of each splitting process, known as the formation time, exceeds the mean free time for collisions with the medium, leading to a significant reduction in the splitting rate, known as the Landau-Pomeranchuk-Migdal (LPM) effect. In the QCD...
The origin of the baryon asymmetry in the Universe (BAU) is a big mystery in particle physics and cosmology. One interesting scenario to explain BAU is the resonant leptogenesis which admits lepton number creation in the electroweak-scale, and therefore, receives lots of phenomenological interests in the LHC era. Then, the decay of right-handed neutrinos which causes the lepton number must be...
We report on simulations of 2-colour QCD with Nf=2 Wilson fermions at nonzero chemical potential and temperature. We present results for the diquark condensate, Polyakov loop and quark number density on finer lattices than those previously reported, as well as ongoing simulations with smaller quark masses. Our results confirm the existence of a "quarkyonic" phase at high density, while the...
We investigate the phase diagram of QCD with heavy quarks at finite temperature and chemical potential in the context of background field methods. In particular, we use a massive extension of the Landau-DeWitt gauge which is motivated by previous studies of the deconfinement phase transition in pure Yang-Mills theories. We show that a simple one-loop calculation is able to capture the richness...
Explaining the matter-antimatter asymmetry of the Universe remains one of the most intriguing problems in particle physics and cosmology. A popular class of theories attributes this asymmetry to CP-violating decays of super-heavy particles in the Early Universe. We present a new source of baryogenesis within these models, and show how the same Yukawa phases which provide the CP-violation for...
The beam energy scan programs at BNL Relativistic Heavy Ion Collider open up a new opportunity to explore the quark-gluon plasma (QGP) at finite densities. The quantitative success of hydrodynamic modeling motivates one to extend the model to lower energies to verify its applicability, to study the transport properties at finite densities, and ultimately to understand the phase structure of...
We will illustrate how a nonperturbative variational technique combined with renormalization group (RG) properties efficiently resums perturbative expansions in thermal field theories. The resulting convergence and scale dependence of optimized thermodynamical quantities are drastically improved as compared to standard perturbative expansions, as well as to other related methods such as the...
We determine the 2+1 flavour equation of state of QCD at finite chemical potential to order $(\mu_B/T)^6$ from lattice simulations. The simulations are performed at
the physical mass for the light and strange quarks on several lattice spacings;
the results are continuum extrapolated. The coefficients of the expansion in
$(\mu_B/T)$ are determined through the analytic continuation from...
We consider the dynamics of the standard model extended by two or more right
handed neutrinos, which simultaneously explains the origin of neutrino masses
through the seesaw mechanism and the baryon asymmetry of the universe
through leptogenesis.
Specifically, we focus on right handed neutrinos with GeV scale mass which can
be found in collider or fixed target experiments.
We use quantum...
Lattice QCD has has the potential to provide urgently needed first principles insight into the binding properties of heavy quarkonium in-medium, which form a central pillar of the experimental investigations of the quark-gluon plasma at the RHIC and LHC collider facilities.
Here we report on progress in our ongoing work to deploy the effective field theory NRQCD on current generation...
Strongly interacting quarks and gluons exposed to a background magnetic field reveal a rich physical structure. This topic has recently become of interest, both because it challenges our understanding of the underlying theory (QCD) as well as due to a wide range of phenomenological applications, from neutron star physics to heavy-ion collisions.
A particularly interesting aspect of this...
The coannihilation rate of kinetically equilibrated non-relativistic
particles plays an essential role in the classic WIMP dark matter
scenario. If the dark matter particles interact attractively, for
instance through Z0 exchange, the coannihilation rate could be
substantially increased with respect to a tree-level estimate, a
phenomenon known as the Sommerfeld effect. We study this...
I will discuss the effect of including a non-minimal coupling between the Higgs field and gravity on vacuum decay in the Standard Model. High precision numerical results indicate that this suppresses vacuum decay relative to flat space calculations, with the minimal suppression near the conformal value of the coupling, $\xi = 1/6$, due to the near-conformal symmetry of the large field 3-loop...
We use the functional renormalization group (FRG) technique to explore the characteristics of the chiral phase transition between the hadronic phase of quantum chromodynamics and the quark-gluon plasma. The restoration of chiral symmetry at high temperatures and/or net-baryon densities leads to changes in the in-medium spectral properties of light vector mesons, directly affecting the dilepton...
We will present recent results regarding chiral symmetry restoration and other hadronic properties at finite temperature. In particular, we will discuss the interpretation of the temperature dependence of lattice screening masses through Ward identities relating pseudoscalar susceptibilities and quark condensates. Such identities are derived for two and three flavours and studied within the...
We address the issue of light scalar fields in de Sitter space using the non perturbative renormalization group. The derivative expansion used in flat space is adapted to this context. At lowest order, the Local Potential Approximation reproduces results of the stochastic approach. We discuss mass and coupling generation as well as radiative symmetry restoration. A simplified first order...
Within the Standard Model there is no electroweak phase transition which could
account for the non-equilibrium physics needed for Baryogenesis. Nevertheless, at temperatures around 160 GeV some interesting features in the equation of state and other thermodynamical functions, e.g. the heat capacity, can be observed. These features of the Standard Model background could have an impact on...
We study a Random Matrix Model for QCD at finite density via Complex Langevin dynamics. This model has a phase transition to a phase with non-zero baryon density. We study the convergence of the algorithm as a function of the quark mass and the chemical potential and focus on two main observables: the baryon density and the chiral condensate. As expected, for simulations close to the chiral...
In many models of electroweak symmetry breaking, the vacuum
structure depends crucially on radiative effects. In order to compute
the decay rate of metastable states, the loop corrections must therefore
be accounted for in the tunneling solitons. In turn, the loops depend on
the solitonic background, such that self-consistent solutions must be
found. We will discuss the relevance of this...
In a theory in which (local) supersymmetry is spontaneously broken for temperatures T \ll M_{pl}, where M_{pl} is the Planck mass, gravitinos couple to MSSM particles via the supercurrent. Thermal gravitino production rate per unit volume due to the strongly interacting sector of the theory can be calculated perturbatively, and to leading order in the QCD coupling \alpha_s(T), is of order...
We show how the increase in the Instanton-dyon density can explain both Confinement and Chiral symmetry breaking. We simulate an ensemble of 64 interacting Instanton-dyons for 2 colors and 0 or 2 quark flavors. We find that at low temperatures, the high density of dyons prefer a symmetric density, which leads to the confining value of the Polyakov Loop. At the same time the Chiral condensate...
The question of whether anomalous, i.e. CP-odd effects, in QCD have been observed in relativistic heavy-ion collisions is a topic of current theoretical and experimental interest. Its solution requires a deeper understanding of how CP-odd domains with chiral imbalance n5, if formed in the collision center, evolve in real-time.
Here we present recent results [1] on a new class of plasma...
In this work we consider the ontological status of the Unruh effect. Is it just a formal mathematical result? Or the temperature detected by an accelerating observer can lead to real physical effects such as phase transitions? In order to clarify this issue we use the Thermalization Theorem to explore the possibility of having a restoration of the symmetry in a system with spontaneous...
A power expansion scheme is set up to determine the Wigner function that satisfies the quantum kinetic equation for spin-1/2 charged fermions in a background electromagnetic field. Vector and axial-vector current induced by magnetic field and vorticity are obtained simultaneously from the Wigner function. The chiral magnetic and vortical effect and chiral anomaly are shown as natural...
A first-order phase transition produces gravitational waves and such a transition only occurs if there is physics beyond the standard model. In this sense gravitational wave experiments can be considered as detectors of new physics. In this talk we review the status of the eLISA experiment and we analyze its capabilities for probing a first-order phase transition. We demonstrate that in some...
We present a first-principles study of the dynamics of the
Chiral Magnetic Effect based on real-time lattice gauge theory
simulations with dynamical fermions. We demonstrate how topological
densities and transitions during the early stages of high-energy
collision lead to the production of axial charge imbalances via the
the axial anomaly and investigate in detail the interplay...
The chiral magnetic effect has attracted much interest in various areas of physics from condensed matter physics to nuclear and particle physics.
In condensed matter physics it has actively investigated in the so called Weyl (semi-)metals in which Weyl fermions are realized as points of band touching with definite topological character.
The chiral magnetic effect arises only in...
Quantum many-body systems far from equilibrium can approach a nonthermal fixed point during their real-time evolution. One example is scalar field theory, which occurs in models of cosmological inflation, and similar examples are found for ultracold Bose gases and for non-Abelian plasmas relevant for heavy-ion collisions. We present two novel far-from-equilibrium universality classes that...
The 125 GeV Higgs may be a singlet under a nonlinearly realised electroweak symmetry. Differing from the SM, anomalous Higgs cubic couplings are then permitted in the potential, which may lead to a first order electroweak phase transition. We find a range of cubic coupling that may lead to observable gravitational waves signatures at interferometer such as eLISA.
We consider gravitational wave production by bubble collisions during a cosmological first-order phase transition. Based on so-called thin-wall and envelope approximations, we estimate gravitational wave spectrum by an analytic way. Our estimation is based on the observation that the two-point correlator of the energy-momentum tensor can be expressed analytically under these assumptions.
A common simplification for describing the early stages of heavy ion collisions is the assumption that incoming nuclei are Lorentz-contracted to infinitely thin "pancakes". This leads to boost-invariance of the produced glasma-state and reduces the system to effectively 2+1 dimensions. This assumption is less justified at lower collision energies. In a recent work [1] we showed how to allow...
We present results from real-time lattice simulations of out-of-equilibrium quark production in non-Abelian gauge theory in 3+1-dimensions. Our simulations include the backreaction of quarks onto the dynamical gluon sector, which is particularly relevant for strongly correlated quarks. We observe fast isotropization and universal behavior of quarks and gluons at weak coupling and establish a...
In various extensions of the Standard Model it is possible that the electroweak phase transition was first order. This would have been a violent process, involving the formation of bubbles and associated shock waves. The collision of these bubbles and shock waves could be a detectable source of gravitational waves. I will summarise the current status of efforts to model the such a phase...
Superfluid vortices in the color-flavor-locked (CFL) phase of dense quark
matter are known to be energetically disfavored relative to well-separated
triplets of so-called semi-superfluid color flux tubes. In this talk we will
present results from our numerical stability analysis of superfluid vortices
in dense quark matter. After identifying (physical) regions of...
The measurements of the Higgs mass and top quark Yukawa coupling indicate that we live in a very special Universe, at the edge of the absolute stability of the electroweak vacuum. The most precise theoretical computations combined with the most recent LHC experiments do not allow us to decide with certainty whether our vacuum is absolutely stable or metastable. In any event, the Standard...
I will review how compact stars can serve as a laboratory for
fundamental physics, and how the latest astrophysical data can be used to put constraints on the properties of dense QCD matter, for example on its equation of state and on hydrodynamical properties of nuclear and quark superfluids. In the second, more specific, part of the talk, I will present latest results on employing...
I will discuss how hydrodynamical flow is reached in heavy-ion collisions
in the limit of weak coupling using an effective kinetic theory description
during the prethermal evolution. I present a Green function that can be
used to provide an initial condition for a hydrodynamical simulation given
the initial geometry.
Gauge/gravity duality (or "holography") allows one to calculate
highly non-trivial far from equilibrium dynamics in strongly coupled
gauge theory --- provided one can solve asymptotically anti-de
Sitter initial value problems in higher dimensional gravity. Recent
results and work in progress in this area will be discussed,
focusing on calculations motivated by the physics of heavy...
