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Dark and the Topic 5 Cold and the Exotic Zoo from the Higgs & to WIMPs & Why is the dark matter probably exotic new from the ?! Contents of Topic 5

In this Topic we delve into the world of new particle to explore possible candidates for particle dark matter. This includes study of what can tell us about - real particle in action. We cover: ‣ The new - examples of exotic new particles ‣ The concept of hot, warm and ‣ and the 2-point spatial correlation function ‣ Introduction to Weakly Interacting Massive Particles (WIMPs) ‣ theory, the LSP, R- and the ‣ Universal extra dimensions and the LKP ‣ Thermal relics and “freeze out” of particles in the Big Bang ‣ The , , Sterile and ‣ Searches for SUSY and UED dark matter at CERN ‣ Axions and how to detect them Towards New Particles in the Cosmos ‣ The evidence is overwhelming that the Universe is filled with material that is non-luminous but exerts powerful gravitational influence on all scales - the Dark Matter. ‣ It is also clear now that this missing can not be normal and , the Big Bang simply did not generate enough , and anyway all searches for non-luminous baryons, like MACHOs don’t find any, or at least not enough. ‣ When we venture into the known but exotic particle world, for instance, Neutrinos and Antimatter, there is slightly more success. We now know neutrinos have some mass. This means that the neutrinos are part of the solution to the dark matter problem. Unfortunately their mass is <1 eV. So the contribution from neutrinos is miniscule. ‣ So we are forced to consider more exotic particle solutions and the possibility of some completely New Physics. Towards New Particles in the Cosmos ‣ Fortunately there are a lot of reasons in particle physics to believe that there exist new as yet undetected particles. ‣ The famous Higgs-Boson is a recent example of a particle predicted to exist and now discovered. ‣ In fact there is a whole zoo of particles postulated by theorists that could explain the dark matter. One example is the Gravitino. This particle is postulated to have no interactions with normal matter, only gravitational effects. This would make it impossible to detect in the laboratory. ‣ Another example is Sterile Neutrinos. These are postulated inert neutrinos that would also interact only via and not via the fundamental interactions of the . ‣ Fortunately there are several well founded candidates that could show themselves by interactions with matter. The New Particle Zoo ‣ Here is a list potential candidate new particles, starting with the most important ones that we will mainly deal with here: (1) LSP (Lightest Supersymmetric Particle), m ~ 10-1000 GeV (2) LKP (Lightest Kaluza-Klein Particle), m ~ 10-1000 GeV (3) , m ~ 10-5 eV ‣ In addition to Gravitinos, ordinary and Sterile Neutrinos, other more exotic examples include: (1) Heavy , m ∼ 2 GeV (2) Ultraheavy, quasi-stable particles, m ∼ 1013 GeV (3) (4) Non-topological solitons and Q-balls (5) QCD nuggets (6) WIMPzillas (7) Primordial Black Holes (PBH), m ≥ 1016 g Cosmology and The Particle Zoo ‣ The theoretical basis for these candidates vary wildly and their and interaction strengths with ordinary matter span many orders of magnitude. So how can we decide which are most likely? ‣ Fortunately this is an amazing example of where cosmology can help with particle physics. We can divide the candidates into two broad types: (1) (HDM) (2) Cold Dark Matter (CDM) ‣ The difference reflects how fast the particles were moving at the they decoupled from the Baryonic Matter (when they stopped interacting with it as the Universe cooled): • HDM refers to particles that are Relativistic at . • CDM refers to slow moving Non-Relativistic candidates. ‣ There is also (WDM), an intermediate form, but there are few candidates in this category. Cosmology and The Particle Zoo ‣ This distinction between HDM and CDM is important because whether dark matter is in the form of slow moving CDM or fast (relativistic) HDM critically influences how we would expect structure in the Universe to form. ‣ Remember which ever it is (CDM or HDM) it dominates the Universe so its bound to affect the structure of the visible bit we can see (, clusters etc.). ‣ This is seen clearly in the results of simulations of Structure Formation in the Universe when CDM or HDM is included, as below. Note how the HDM case has less structure.

CDM HDM Hot Dark Matter ‣ So Hot Dark Matter (HDM) is a particle species that Decouples, or “Freezes Out” when its interaction rate drops below the Hubble Expansion Rate when the particle’s velocity is still relativistic. ‣ An example of HDM is the with mass m ~ eV. ‣ On small scales HDM particles move too quickly to participate in Gravitational Clustering. But on larger scales they can cluster just like heavy matter. The transition occurs around the size of clusters of galaxies ~ 10 Mpc. ‣ So HDM tends to smooth out structure so that Large Scale Structure (on the scale of ) persist but small scale structure (like galaxies) do not readily form. ‣ To fit observation this suggests a Top-Down Scenario for the formation of the Universe where large scale structure forms first and breaks up into small scale structure later. Cold Dark Matter ‣ Cold Dark Matter (CDM) has the reverse characteristic of HDM. The particles hardly move after decoupling, they are non-relativistic, and their masses are larger. ‣ This favours a Hierarchical Clustering scenario where small structure forms first and then collects into larger structure later. So we have a so-called Bottom-Up scenario. ‣ Here is a so-called N-Body Simulation, showing such a Bottom-Up scenario with CDM. The Universe starts with small structures that cluster time into larger scale structure later. ‣ Such simulations provide a powerful tool for cosmologists to examine HDM vs. CDM scenarios and hence what particle physics works - this is real Particle Astrophysics in action! HDM vs. CDM & Structure Formation ‣ A critical issue with these simulations is how to quantify the amount of clustering of matter, or the amount of density fluctuations, vs. scale and compare this for the two cases where the dark matter is either HDM or CDM. Then to compare the results with real observations. ‣ Basically we need to compare the Spatial Distribution of masses in the Universe predicted by the simulations with that actually observed. The best way to do this to use a so called the Two-point Spatial Galaxy Correlation Function. ‣ Suppose N points are distributed in a volume V. The density is then n = N/V. If the points are randomly distributed in the sky then the probability that a given point has a neighbour in a surrounding volume is δP = nδV

€ HDM vs. CDM & Structure Formation ‣ Now if there is correlation between the points we can rewrite this in terms of the Two-point Spatial Galaxy Correlation Function as distance from the first point nδV[1+ ξ(r)]

two-point correlation function ‣ In this equation if the points (galaxies) are in random locations then = 0. Any clustering would mean > 0. € ‣ Observations of galaxies and clusters can be used to determine and hence the size of Density Fluctuations vs. Scale that can be compared with different simulations of Structure Formation with Hot or Cold Dark Matter. ‣ The following plot shows one result compared with data. HDM vs. CDM & Structure Formation ‣ The plot here shows Density Fluctuations (relative units) vs. Scale (in lightyears). ‣ The various points are data from different observations spanning a huge range of scale including the CMBR. ‣ The green and red lines show the expectation if CDM or HDM is the dark matter. ‣ Note that although both HDM and CDM models fit the data well at very large scale (right part of plot), HDM completely fails at smaller scale. HDM simply does not produce enough small scale structure. So CDM clearly wins! ‣ This is more strong evidence against neutrino dark matter. CDM and The Particle Zoo ‣ So the observational evidence combined with structure formation simulations strongly favours CDM Particles and a Bottom-Up Scenario whereby small-scale structure forms first and later clusters into larger structures. In the HDM scenario, with relativistic particles such as neutrinos, the small scale structure gets washed-out. ‣ Out of the this leaves us with three theoretically well motivated main candidates, all CDM type: Supersymmetry theory Weakly (1) LSP - Neutralino Particles Interacting (2) LKP - Kaluza-Klein Particles Massive Extra Dimension theory Particles (3) Axions CP violation theory ‣ We will do these in detail but note first the classification of (1) & (2) - Weakly Interacting Massive Particles (WIMPs). What Does WIMP Mean? ‣ We’ll cover these most important candidates and the particle physics theories behind them in more detail now but first what do we mean by the term WIMP and what is a WIMP? ‣ WIMP is an generic term that refers to any type of dark matter candidate particle with the following characteristics: (1) Weakly Interacting - meaning interaction strengths (cross- sections) with normal matter are as weak or weaker than the Weak Force (the force that governs ) (2) Massive - typically > ~ 1 GeV and up to ~10,000 GeV (3) Non Relativistic - slow moving, typically ~ 10-3 c (4) Neutral - in fact no can be the dark matter because it would interact too easily with normal matter ‣ All WIMPs count as CDM. Axions also count as CDM but they are not WIMPs. To understand the difference we need to return to the Big Bang and the early Universe. Big Bang Creation & Thermal Relics ‣ A vital difference in particles formed in the Early Universe is between those created Thermally or Non-Thermally. WIMPs are created thermally, while Axions are not. ‣ In Thermal Creation in the hot, dense, early Universe, we have Thermal Equilibrium and the number density of DM particles (e.g. WIMPs) roughly equals that of the

‣ As the Universe cools the WIMP and numbers at first decrease together. When the temperature drops below the WIMP Mass, creation of WIMPs needs photons on the high tail of the thermal distribution, so the number density starts to drop exponentially . ‣ However, the Universe is expanding so at some point the probability of a WIMP finding another to annihilate with

becomes zero so the number density reaches “Freeze-Out”. Big Bang Creation & Thermal Relics ‣ What “Freeze-Out” means is that for this thermal process, provided the hypothetical particles are stable, we expect to generate a fixed population of particles, as shown here: ‣ An accurate prediction can be made of the expected number Freese-out with increasing density using the Boltzmann equation but roughly we get

where < σv > is the thermally averaged Cross Section for two

WIMPs to annihilate each other. ‣ Note, if we want WIMPs to be the dark matter (i.e. ΩWIMP ~ 0.25) then it turns out < σv > ~ 1 pb and MWIMP ~ 100 GeV. Thermal Relics & Particle Physics ‣ The fact that we get < σv > ~ 1 pb is remarkable because this is just what is expected for particles with Electroweak Scale interactions. There are several problems with the Standard Model of particle physics which are solved by new electroweak scale physics theories that also predict existence of new particles with this sort of cross section. ‣ So particle physics, independent of any cosmology, appears to predict existence of new particles and it happens that the characteristics of these, the cross sections and mass, are just what is needed for Thermal Relic WIMP Dark Matter. ‣ These are powerful arguments that WIMPs could be the dark matter, from basic particle physics and cosmology. ‣ But we know the Electroweak Scale already has the W & Z Particles in the Standard Model around the right rest energy (90 GeV for the W), so why do we need new theories at all? Dark Matter in the Standard Model? ‣ The Standard Model (SM) of Particle Physics is illustrated opposite: ‣ The Standard Model is a Field Theory. It summarises our best understanding of the forces of (except gravity) and all the known particles in nature. ‣ According to the Standard Model, the only stable particles are: (i) , (ii) Up/Down , (iii) Neutrinos. ‣ So although the W and Z have about the right rest energy they are unstable and so can not explain the Dark Matter. ‣ But what about the Electrons, Quarks and Neutrinos? Dark Matter in the Standard Model? ‣ Well the Quarks interact by the Strong Force and are charged, and the Electrons interact by the Electroweak Force and are also charged. We know a lot about them, they are bound in (Baryonic Matter) and are can easily be detected. They can not be the Dark Matter. ‣ The Neutrinos we have explored already. They interact very weakly (only by the ), have no EM charge but are highly abundant. ‣ They are also relativistic, and so travel too fast to cause galactic scale clumping (they are Hot Dark Matter). ‣ However, we now know they do have a tiny mass, so in fact do contribute to the mass of the Universe, ~0.3%. Is the Higgs Boson Dark Matter? ‣ On 4 July 2012, the discovery was announced at the Large of a new particle with a mass between 125 and 127 GeV, the Higgs Boson. An amazing achievement and success that confirms the existence of the Higgs Field. ‣ Proof of the presence of this field is the last “missing piece” of the Standard Model. It is vital because it explains why some fundamental particles have mass, a key fact previously not explained in the Standard Model. ‣ The Higgs Field permeates the entire Universe. It is excitations of this field that manifest itself as Higgs Particles. ‣ So can the Higgs Boson be the Dark Matter? Unfortunately no. Again, although it has a WIMP-like mass, Higgs are fleeting, unstable beasts. They can not form the DM. ‣ Interestingly though, some Supersymmetry Theories, do predict that the Higgs may decay into dark matter particles. WIMPs in SUSY and UED ‣ So the Standard Model simply can not provide the particles we need. We are going to need new particle physics theories. Thankfully there are two particularly well motivated ideas and both predict WIMP-like particles: (1) Supersymmetry (SUSY) - this predicts new so-called Supersymmetric Particles. The lightest of these can be stable, the Lightest Supersymmetric Particle (LSP). (2) Universal Extra Dimensions (UED) also predicts new particles. The lightest of these can also be stable and so be dark matter, the Lightest Kaluza-Klein Particle (LKP). ‣ Both these theories are well founded and predict these new, non-relativistic particles, produced thermally in the Big Bang just as expected for WIMPs and for Cold Dark Matter particles. However, SUSY has gained the most popularity. Supersymmetry and Dark Matter ‣ SUSY Theory is complicated and outside our scope here but we can outline the main features. Firstly, the motivation is to solve various problems with the Standard Model (SM): ‣ For instance, SM is incompatible with , it can’t account for the weakness of gravity or the huge energy scale between SM Interactions and the Planck Scale. ‣ A particular aim of SUSY is to provide a mechanism by which all the forces of nature can be unified. At higher , where are unbroken, we might expect a unified theory should have a single coupling constant. This is the so-called Grand Unified Theory, illustrated here. Supersymmetry (SUSY) Theory ‣ The concept of SUSY Theory entails giving every known particle in the Standard Model a so-called Super Partner with differing by 1/2 such that all SM get a Bosonic Partner and all SM Bosons a Fermionic Partner:

• Quarks (spin-1⁄2 fermions) → squarks (spin-0 bosons)

• Leptons (spin-1⁄2 fermions) → sleptons (spin-0 bosons)

• , photons, W, Z Bosons (spin-1 bosons) → (spin-1⁄2 fermions) • Higgs (spin-0 bosons) → (spin-1⁄2 fermions)

‣ Note the name changes here, with an “s…” in front for the new bosons and “…ino” at the back for the new fermions. The Lightest Supersymmetric Partner ‣ So SUSY postulates the existence of this kind of “Shadow Population” of new particles formed in the Big Bang. ‣ This concept does indeed neatly provide a mechanism for including gravity in the Standard Model and for unifying the Electromagnetic, Strong & Weak interactions in one force. ‣ But what does this mean for Dark Matter? ‣ Well, this new set of particles has a range of properties, like mass and lifetime. Whilst they are generally expected to be short-lived, in turns out that the lightest one, the so-called Lightest Supersymmetric Partner (LSP) could be stable. Hence the LSP could make up the Dark Matter. ‣ For the LSP to be stable it turns out that the interactions of SUSY particles need to conserve so-called R-Parity. ‣ Thus if R-Parity is conserved, the LSP is stable and we have our dark matter candidate. So what is R-Parity? R-Parity in SUSY ‣ In all Standard Model Interactions certain Quantum Numbers are conserved, namely ‘ number’ B, ‘ number’ L and ‘Spin’ S. That is, the amount of these quantities must be the same before and after any SM particle interactions. ‣ R-Parity is a quantity made from these quantum numbers as: R = (-1)3(B-L)+2S R = +1 for Particles; R = -1 for Sparticles

‣ Now when SUSY is added, and where we need to consider interactions between Particles and Sparticles (the new SUSY particles), it turns out that B and L are no longer conserved but that R-Parity IS conserved, at least in so- called Minimal SUSY Standard Models (MSSMs). R-Parity Conservation in SUSY ‣ Note R-Parity is a Multiplicative - i.e. in a particle (sparticle) interaction if you find the value of R for each object before the interaction and multiply them together, and you do the same for all the objects after the interaction, the two numbers you get must be the same or the interaction is not allowed. ‣ For instance, the following example generic interactions are allowed when R-Parity is Conserved: (i) N → SS (ii) NS → NS here N signifies a “normal” fundamental particle and S a SUSY particle where (i) is a decay, (ii) a two body interaction. ‣ Note there are possible SUSY Models in which R-Parity is not conserved. In this case the LSP would decay and we would not have a dark matter candidate? ‣ So what form does the LSP take if R-Parity is conserved? What is the LSP? ‣ There are various possibilities for what a stable LSP could be in SUSY theory but the three most important, all of which could explain the Dark Matter, are: (1) The Gravitino (2) The Sneutrino (3) The Neutralino ‣ Gravitino Dark Matter comes from SUSY models where the scale of Supersymmetry Breaking is low, ~100 TeV. The Gravitino is very , ~ eV with interaction strength much weaker than other SUSY DM candidates. As dark matter, the Gravitino is sometimes called a Super-WIMP. ‣ Sneutrino Dark Matter involves interaction via Z Bosons. It is actually ruled out in Minimal Supersymmetric Models but the possibility of extended models with Sterile Neutrinos have reopened the idea. More on this later. ‣ Neutralino Dark Matter appears the most likely possibility for the LSP, so we’ll cover this in more detail now. The Neutralino Particle ‣ In SUSY various Super Particles can mix to form a set of so-called Neutralino States labelled . ‣ The best motivated of these involves a mixture of Higgsinos, a Wino (the W Boson Super Partner) and a particle called the Bino, so that we have:

‣ There are 4 states allowed, typically labelled (the lightest), , and (the heaviest). ‣ With R-Parity conserved the Lightest Neutralino is stable and all supersymmetric cascade-decays end up decaying into this particle the , often abbreviated to simply . ‣ Note that are so-called Majorana Fermions, which just means that they are their own anti-particles. Thus if two neutralinos meet, they will annihilate each other. Neutralino Dark Matter Summary ‣ The Neutralino is a major advance now widely regarded as the most likely explanation for Dark Matter. It is now the subject of a massive world-wide race to prove that it exists. It’s worth summarising how we got to this conclusion: ‣ Cosmology, BBNS, CMBR and observations tell us most of the mass of the Universe is Dark Matter and that it’s not Baryons but other particles. Cosmology tells us to expect them to be slow moving Cold Dark Matter. Consideration of thermal particle production in the early Universe helps us favour a generic particle type we call Weakly Interacting Massive Particles. Independently theoretical particle physics, needed to solve failings on the standard model, lead us to postulate SUSY theory. This predicts a Lightest Supersymmetric Particle (LSP) that is stable if R-Parity is conserved. The Neutralino looks to be the most likely LSP. Beyond SUSY ‣ Extending the SM to include SUSY fixes lots of problems and leads naturally to the LSP and the Neutralino, which fits well as a WIMP explanation for Dark Matter. But there are other well motivated candidates, most importantly the Axion, which is not a WIMP, and the LKP that comes from Universal Extra Dimension Theory and does fall in the category of WIMP. We’ll cover the axion separately (both the physics and how to detect it) but finish here with the KLP and also the new possibility of so-called Sterile Neutrinos. Universal Extra Dimensions (UED) ‣ Just as extending SM with SUSY fixes problems we find extending General Relativity to include extra-dimensions also fixes problems there, notably why gravity is so weak. ‣ Along the way UED also predicts new stable particles with WIMP characteristics just like the LSP, it’s called the Lightest Kaluza-Klein Particle (LKP). ‣ The basis is UED comes from the questions why can’t there be more than 4 dimensions? (there’s no good reason) and what does dimension mean anyway? (dimensions are

independent in which a single value is required to

specify a position in that dimension).. ‣ So in fact General Relativity can be extended to any number of extra dimensions and this changes the strength of gravity in our dimensions. Extra-dimensions can also be used to incorporate additional forces into General Relativity. Compact Extra Dimensions ‣ If there are extra-dimensions, they must be different to the ‘every day’ infinitely long dimensions. They could be Compact Extra Dimensions, which are too small to see. ‣ The In the 1920s/30s, the Kaluza-Klein Theory incorporated one compact extra-dimension into General Relativity, in order to unify and gravity. ‣ For N extra-dimensions which are visible on the scale of radius R then gravity is modified (eg Newtonian gravity): ‣ So the gravitational coupling G could appear very small at large distances, but is in fact similar to the SM forces if we consider all the dimensions relevant to gravity. Compact UED Dark Matter ‣ Consider the energy of a single particle moving in an extra- dimension of size R:

‣ From the momentum of the an excitation (‘particle’) over a length R is given by 2 2 2 2 2 ‣ Recalling that (m’’c ) = (pextra c) + (mc ) means that every particle moving in the extra dimension has an infinite

number (n) of higher mass partners. Compact UED Dark Matter ‣ Unlike SUSY Partners, these partners would be identical to the SM particles, only with higher mass. As with our familiar large spatial dimensions, you have to conserve momentum in interactions. ‣ Kaluza-Klein Particles have momenta in units of n so for example (considering neutral particles): ‣ When n = 3, the particle can decay to: ‣ two partner particles with n = 1 and n = 2 ‣ three partner particles each with n = 1 ‣ When n = 2, the particle has to decay to two partner particles each with n = 1. ‣ When n = 1, the particle can’t decay. ‣ So in order to conserve momentum in the extra-dimensions, the Lightest Kaluza-Klein Particle must be stable. Has SUSY and UED Been Found ‣ One of the aims of the (LHC) at CERN is to search for evidence of SUSY and UED particles by trying to create them in the -proton collisions and detect them in the ATLAS or CMS Experiments. ‣ These detectors are capable of measuring charged tracks, Hadronic and electromagnetic energy deposits. They can identify Hadronic “Jets”, Electrons, Photons and . ‣ Unfortunately, SUSY or UED particles can’t ATLAS be directly detected, only inferred by looking for missing energy in the reactions and assuming the missing part is due to them. ‣ Many Reaction Channels have been studied with nothing found so far but a recent increase in LHC power may change this. Has SUSY and UED Been Found? ‣ Here are some example reactions that produce SUSY or UED dark matter in the form of Feynman Diagrammes. Note that any new ‣ proton slepton lepton particle like this will neutralino quickly escape the Example detector. So we have SUSY no way of knowing reaction what it’s Lifetime is. ‣ So since to be a dark matter candidate the particle must be stable gamma-ray then even if evidence is Example found in the LHC, we UED UED LKP can not be 100% sure reaction it is dark matter. Sterile Neutrinos ‣ Another possible candidate that is gaining support is the so- called Sterile (or Inert) Neutrino, different from the Active Neutrinos in the standard model discussed before. ‣ The three known neutrino types have Left Handed Spin, so theorists argue others should exist with Right Handed Spin as is true for all other Fermions (e.g. the photon). ‣ It is thought Sterile Neutrinos could be produced in the Big Bang. Their mass would be higher than the active ones but they would interact with normal matter only through gravity. ‣ Although their lifetimes would be long enough to form dark matter, with masses and velocities consistent with Cold (or Warm) Dark Matter, a problem has been that some should decay to produce observable x-rays. ‣ Recently unexplained x-rays have been detected in galaxy clusters consistent with decay of a 7 keV . Towards Axions as Dark Matter ‣ So far we have seen that cosmology favours Cold Dark Matter and that this leads us to postulate new generic class of particles we call WIMPs. Meanwhile, particles with the required properties to be WIMPs are well motivated by particle physics theories, in particular SUSY, that predicts existence of the LSP in the form of the Neutralino particle, and UED, that gives us the LKP. ‣ Both these could be the dark matter. But we find other possibilities, such as the Gravitino, that would be essentially impossible to detect, and the Sterile Neutrino. ‣ But there is another well motivated alternative that is not classed as a WIMP (it is not produced thermally) but would be Cold Dark Matter - namely the Axion. ‣ Ed Daw is an expert on Axions - the following are notes from his class on Axions and how they might be detected: What are Axions Why Were Axions Invented? The Strong CP Problem The Peccei-Quinn Mechanism The Snooker Ball Sees the Wider World Why is the Table Flat ? Restoration at Low Energies Axion Couplings Axion Properties and Mass What is the Axion Mass ? Detecting Axions in Our Basics of Resonant Cavity Detectors Axion Line Width A Resonant Cavity for Axion Searches Cavity and Receiver Electronics Noise Background Signal Power The Radiometer Equation Rescues us Axion Search Results What About non Dark Matter Axions? Axion Summary Summary of Topic 5 A guide for the exam ‣ The cosmological arguments that lead us to postulate different types of new particles as the explanation for dark matter - understand hot, warm and cold dark matter and how studies of structure formation teach us about these. ‣ Understand what WIMPs are and the idea of thermal relic particles formed in the early Universe including “freeze-out”. ‣ Know the basics of the standard model of particles and how this leads to supersymmetry theory - the LSP and neutralino, why the Higgs Boson and other SM particles are not dark matter. ‣ Understand the basics of Universal Extra Dimension particles and exotics like sterile neutrinos and gravitinos. ‣ Know about accelerator searches for dark matter. ‣ Axions are the subject of much research in dark matter - be aware of the motivation for axions and how to detect them. Terms to know from Topic 5 A guide for the exam ‣Antimatter, Higgs Boson, Gravitino, Sterile Neutrinos ‣Weakly Interacting , WIMP, Thermal Relic, Freese-out ‣Hot, Warm, Cold Dark Matter, Top-Down and Bottom-Up Structure ‣Hierarchical Clustering, N-Body Simulation, 2-Point Correlation Function ‣Density Fluctuation Power Spectrum ‣Supersymmetry, SUSY, Lightest Supersymmetric Particle, Neutralino ‣Universal Extra Dimensions (UED), Lightest Kaluza-Klein Particle (LKP) ‣Electroweak Scale, W & Z particles, Standard Model, Quarks, Higgs Field ‣Bosonic Partner, Fermionic Partner Squaks, Sleptons, ‣Shadow Matter, R-Parity, Minimal SUSY Standard Model (MSSM) ‣Large Hadron Collider (LHC), CERN, ATLAS, CMS, Hadronic Jets ‣Axions, CP Violation, Peccei Quinn Mechanism ‣Resonant Cavity, Line Width, Johnson Noise, Quality Factor Q, ADMX Questions on Topic 5 to help with exam revision ‣ Briefly explain “Freeze-Out” of thermal relic dark matter particles. ‣ Give three differences between hot and cold dark matter. ‣ Give three characteristics of Weakly Interacting Massive Particles ‣ What does a two-point spatial galaxy correlation value of > 0 mean? ‣ Draw a plot to show how the size of density fluctuations changes with scale in the Universe. ‣ Why are , nor the Higgs Boson, dark matter. ‣ How are SUSY particle different from standard model particles? ‣ Explain how conservation of R-parity determines what interactions are allowed between normal and SUSY particles. ‣ What is meant by Majorana ? ‣ Why can the LHC never truly confirm the existence of dark matter particles? ‣ Explain the difference between normal neutrinos and sterile neutrinos. ‣ What is the particle physics motivation for postulating axions and how might the ADMX experiment detect them in the laboratory? Equations from Topic 5 Equation reminders for the exam

nδV[1+ ξ(r)]

R = (-1)3(B-L)+2S €

2 2 2 2 ‣ (m’’c ) = (pextra c) + (mc2)