Consequences of Supersymmetry in the Early Universe

Currently, we live in an era characterized by the completion and first runs of the LHC accelerator at CERN, which is hoped to provide the first experimental hints of what lies beyond the Standard Model of particle physics. In addition, the last decade has witnessed a new dawn of cosmology, where it has truly emerged as a precision science. Largely due to the WMAP measurements of the cosmic microwave background, we now believe to have quantitative control of much of the history of our universe. These two experimental windows offer us not only an unprecedented view of the smallest and largest structures of the universe, but also a glimpse at the very first moments in its history. At the same time, they require the theorists to focus on the fundamental challenges awaiting at the boundary of high energy particle physics and cosmology. What were the contents and properties of matter in the early universe? How is one to describe its interactions? What kind of implications do the various models of physics beyond the Standard Model have on the subsequent evolution of the universe? In this thesis, we explore the connection between in particular supersymmetric theories and the evolution of the early universe. First, we provide the reader with a general introduction to modern day particle cosmology from two angles: on one hand by reviewing our current knowledge of the history of the early universe, and on the other hand by introducing the basics of supersymmetry and its derivatives. Subsequently, with the help of the developed tools, we direct the attention to the specific questions addressed in the three original articles that form the main scientific contents of the thesis. Each of these papers concerns a distinct cosmological problem, ranging from the generation of the matter-antimatter asymmetry to inflation, and finally to the origin or very early stage of the universe. They nevertheless share a common factor in their use of the machinery of supersymmetric theories to address open questions in the corresponding cosmological models.Hiukkasfysiikka ja kosmologia ovat havaitun maailmankaikkeuden kaikkein pienimmän ja suurimman skaalan rakenteita tutkivat fysiikan alat: hiukkasfysiikassa pyritään ymmärtämään luonnon perusosasten luonne ja vuorovaikutukset, kun taas kosmologia tutkii maailmankaikkeuden syntyhistoriaa sekä nykyistä rakennetta. Näiden kahden näennäisesti toisistaan hyvin kaukaisen alan yhtymäkohta löytyy varhaisesta maailmankaikkeudesta, jossa Big Bang -teorian mukaan universumin täytti erittäin kuuma ja tiheä hiukkaspuuro. Tämän aineen ominaisuuksien ymmärtäminen on yhtäällä välttämätöntä maailmankaikkeuden myöhemmän kehityksen ennustamiseksi, mutta toisaalta - johtuen valtavasta energiatiheydestä - vaatii myös hiukkasfysiikan syvällistä hallintaa. Elämme tällä hetkellä ajanjaksoa, joka on niin hiukkasfysiikan kuin kosmologian kannalta ainutlaatuinen. CERN-laboratoriossa Sveitsissä on hiljattain käynnistetty kaikkien aikojen tehokkain hiukkaskiihdytin LHC, jonka toivotaan antavan ensimmäisiä viitteitä tämänhetkisen hiukkasfysiikan yleisesti hyväksytyn teoriarakennelman, ns. Standardimallin, ulkopuolisesta fysiikasta. Toisaalta viimeisten kymmenen vuoden aikana kosmologiasta on vihdoin muodostunut tarkkuustiede, kun kosmisen mikroaaltotaustasäteilyn spektriä tutkivan WMAP-satelliitin tuloksista on pystytty päättelemään maailmankaikkeuden historiaa ja nykyrakennetta kuvaavia parametreja huomattavasti entistä tarkemmin. Samalla kun kokeellisen hiukkasfysiikan ja kosmologian nopea kehitys on avaamassa aivan uudenlaisia ikkunoita maailmankaikkeuden syntyyn ja kehitykseen, se myös lähettää haasteen teoreettiselle fysiikalle: tänä päivänä on entistäkin tärkeämpää pystyä laskemaan Standardimallin ulkopuolisista teorioista seuraavia ennusteita kosmologisille parametreille. Erityisen polttavia ovat kysymykset siitä, mitä seurauksia ns. supersymmetrisillä teorioilla on varhaisen maailmankaikkeuden kehitykselle. Supersymmetrian on nimittäin otaksuttu tarjoavan vastauksen useisiin nykyfysiikan suurimmista avoimista kysymyksistä aina pimeästä aineesta ns. hierarkiaongelmaan, ja siksi sen kosmologiset implikaatiot ovatkin yksi modernin korkeaenergiafysiikan keskeisimmistä tutkimuskohteista. Käsillä olevassa väitöskirjatyössä luodaan katsaus erilaisten supersymmetristen teorioiden ominaisuuksiin ja niiden merkitykseen varhaisen maailmankaikkeuden kehitykselle. Työ alkaa johdanto-osalla, joka luo yleiskatsauksen alaan ja johdattelee lukijan väitöskirjan kolmen alkuperäisartikkelin aihepiireihin, jotka kaikki liittyvät kosmologisten ongelmien ratkaisuun supersymmetristen kenttäteorioiden keinoin. Ensimmäisessä artikkeleista tarkastellaan erästä ratkaisua hyvin tunnettuun ns. leptonituoton ongelmaan supersymmetrisissä teorioissa, jonka avulla maailmankaikkeudessa havaittu materian ja antimaterian välinen asymmetria pyritään selittämään. Muut artikkelit puolestaan liittyvät ns. MSSM-inflaatioon sekä säiekaasukosmologiaan, joihin liittyviä käsitteellisiä ja laskennallisia ongelmia niissä ratkaistaan

Supergravity origin of the MSSM inflation

We consider the supergravity origin of the recently proposed MSSM inflationary model, which relies on the existence of a saddle point along a dimension six flat direction. We derive the conditions that the Kahler potential has to satisfy for the saddle point to exist irrespective of the hidden sector vevs. We show that these conditions are satisfied by a simple class of Kahler potentials, which we find to have a similar form as in various string theory compactifications. For these potentials, slow roll MSSM inflation requires no fine tuning of the soft supersymmetry breaking parameters.Comment: v3: 10 pages, no figures; version accepted for publication. Typos correcte

On the origin of thermal string gas

We investigate decaying D-branes as the origin of the thermal string gas of string gas cosmology. We consider initial configurations of low-dimensional branes and argue that they can time evolve to thermal string gas. We find that there is a range in the weak string coupling and fast brane decay time regimes, where the initial configuration could drive the evolution of the dilaton to values, where exactly three spacelike directions grow large.Comment: 16 pages, 4 figures, v2: references adde

Python tools for simulating beam dynamics

Brief explanation of requirements for fast beam dynamics simulations, why Python, and the PyHEADTAIL package

Summary of modelling studies on the beam induced vacuum effects in the FCC-hh

EuroCirCol is a conceptual design study of a Future Circular Collider (FCC-hh) which aims to expand the current energy and luminosity frontiers that the LHC has established. The vacuum chamber of this 50 TeV, 100 km collider, will have to cope with unprecedented levels of synchrotron radiation power for proton colliders, dealing simultaneously with a tighter magnet aperture. Since the high radiation power and photon flux will release large amounts of gas into the system, the difficulty to keep a low level of residual gas density increases considerably compared with the LHC. This article presents a study of the beam induced vacuum effects for the FCC-hh novel conditions, the different phenomena which, owing to the presence of the beam, have an impact on the vacuum level of the accelerator. To achieve this, a novel beam screen has been proposed, featuring specific mitigating measures aimed at dealing with the beam induced effects. It is concluded that thanks to the new beam screen design, the vacuum level in the FCC-hh shall be adequate, allowing to reach the molecular density requirement of better than $1 \times 10^{15}$ H$_2$/m$^3$ with baseline beam parameters within the first months of conditioning

Reconstruction of the SEY evolution during the 2022 LHC scrubbing run

During each long shutdown of the Large Hadron Collider (LHC), the surface of the beam screens are expected to decondition, favoring the formation of dense electron clouds, which generate high heat loads on the cryogenic system of the superconducting magnets. A scrubbing run took place soon after the restart of the LHC for Run 3 (2022) in order to recondition the beam screens and limit the electron cloud formation such that the induced heat loads can be handled by the cryogenic system. We performed electron cloud build-up simulations using real beam data extracted from the LHC logging system and inferred the Secondary Emission Yield (SEY) by comparing simulations with experimental measurements of heat load. The vast amount of data that is logged during the scrubbing run allowed the systematic study of the SEY and its evolution in different regions like the regular arc half-cells and the instrumented half-cells. Finally, a method was defined and used in order to disentangle the heat load contribution of the dipole and quadrupole magnets in a half-cell when only the total heat load is available

Numerical modeling of fast beam ion instabilities

The fast beam ion instability may pose a risk to the operation of future electron accelerators with beams of high intensity and small emittances, including several structures of the proposed CLIC accelerator complex. Numerical models can be used to identify necessary vacuum specifications to suppress the instability, as well as requirements for a possible feedback system. Vacuum requirements imposed by the instability have previously been estimated for linear CLIC structures, using the strong-strong macroparticle simulation tool FASTION. Currently, efforts are being made to improve the simulation tools, and allow for equivalent studies of circular structures, such as the CLIC damping rings, on a multi-turn scale. In this contribution, we review the recent code developments, and present first simulation results

Numerical simulations studies on single-bunch instabilities driven by electron clouds at the LHC

Instabilities driven by electron clouds in the LHC are studied by means of numerical simulations performed with the PyECLOUD-PYHEADTAIL suite. Particular attention is given to instabilities driven by e-cloud in the quadrupole magnets at injection energy, which are found to be the most critical case. The numerical parameters of the simulation (grids, number of macroparticles) are defined based on extensive convergence scans, which provide useful guidelines also for future simulation studies. The dependence of the beam stability on RF voltage, bunch intensity, transverse emittance, chromaticity and octupoles settings is investigated. The spectral properties of the unstable motion are analyzed. Simulations are also performed for less critical cases, namely instabilities driven by the quadrupoles at collision energy and instabilities driven by the dipoles at injection energy

Non-monotonic dependence of heat loads induced by electron cloud on bunch population at the LHC

Electron cloud effects are among the main performance limitations for the operation of the Large Hadron Collider with 25 ns bunch spacing. Electrons impacting on the beam screens of the superconducting magnets induce a significant heat load reaching values close to the full cooling capacity available from the cryogenic system in some LHC sectors. To better understand this performance limitation, numerical simulations with the PyECLOUD code were performed to study the dependence of the heat load on different beam and machine parameters, in particular the bunch population, which is foreseen to be considerably increased with the impending HL-LHC upgrade. The simulations predict a complex, non-monotonic behavior of the heat load with bunch population which has important implications in defining the upgrade of the cryogenic system required for coping with HL-LHC beam intensities. An in-depth analysis of the simulation results shows that the non-monotonic dependence of the heat load on the bunch population is driven by an interplay between the spectrum of the impacting electrons and the shape of the Secondary Electron Yield curve. Experimental data were collected at the LHC during normal operation and dedicated experiments in order to validate the simulation model and confirm the expected non-monotonic behavior. The simulation results are found to reproduce very well the measurement data