Composite dark matter and LHC interplay

In composite Higgs models the pseudo-Nambu-Goldstone Boson (pNGB) nature of the Higgs field is an interesting alternative for explaining the smallness of the electroweak scale with respect to the beyond the Standard Model scale. In non-minimal models additional pNGB states are present and can be a Dark Matter (DM) candidate, if there is an approximate symmetry suppressing their decay. Here we assume that the low energy effective theory (for scales much below the compositeness scale) corresponds to the Standard Model with a pNGB Higgs doublet and a pNGB DM multiplet. We derive general effective DM Lagrangians for several possible DM representations (under the SM gauge group), including the singlet, doublet and triplet cases. Within this framework we discuss how the DM observables (relic abundance, direct and indirect detection) constrain the dimension-6 operators induced by the strong sector assuming that DM behaves as a Weakly Interacting Particle (WIMP) and that the relic abundance is settled through the freeze-out mechanism. We also apply our general results to two specific cosets: SO(6)/SO(5) and SO(6)/SO(4)×SO(2), which contain a singlet and doublet DM candidate, respectively. In particular we show that if compositeness is a solution to the little hierarchy problem, representations larger than the triplet are strongly disfavored. Furthermore, we find that composite models can have viable DM candidates with much smaller direct detection cross-sections than their non-composite counterparts, making DM detection much more challenging.

The initial density of dark matter (DM) particles, otherwise secluded from the standard model (SM), may be generated at reheating, with an initial temperature ratio for internal thermalizations, ξi=TDM,i/TSM,i. This scenario necessarily implies inflaton-mediated scatterings between DM and SM after reheating, with a rate fixed by the relic abundance of DM and the reheat temperature. These scatterings can be important for an inflaton mass and reheat temperature as high as O(107 GeV) and O(109 GeV), respectively, since the thermally averaged collision terms become approximately independent of the inflaton mass when the bath temperature is larger than the mass. The impact of these scatterings on DM cosmology is studied modeling the perturbative reheating physics by a gauge-invariant set of inflaton interactions up to dimension 5 with the SM gauge bosons, fermions, and the Higgs fields. It is observed that an initially lower (higher) DM temperature will rapidly increase (decrease), even with very small couplings to the inflaton. There is a sharp lower bound on the DM mass below which the relic abundance cannot be satisfied due to faster backscatterings depleting DM quanta to SM particles. For low DM masses, the cosmic microwave background constraints become stronger due to the collisions for ξi<1, probing values as small as O(10−4), and weaker for ξi>1. The big-bang nucleosynthesis constraints become stronger due to the collisions for lower DM masses, probing ξi as small as O(0.1), and weaker for higher DM mass. Thus inflaton-mediated collisions with predictable rates, relevant even for high-scale inflation models, can significantly impact the cosmology of light DM. Published by the American Physical Society 2024

Lectures on flavor physics presented at the 2012 CERN HEP Summer School. Content: 1) flavor physics within the Standard Model, 2) phenomenology of B andD decays, 3) flavor physics beyond the Standard Model. In the limit of unbroken electroweak symmetry none of the basic constituent of matter could have a non-vanishing mass. The problem of quark and lepton masses is therefore intimately related to the other big open question in particle physics: which is the mechanism behind the breaking of the electroweak symmetry, or which is the mechanism responsible for the non-vanishing masses of the weak force carriers (theW andZ bosons). Within the SM these two problems are both addressed by the Higgs mechanism: the masses of quarks and leptons, as well as the masses ofW andZ bosons, are the result of the interaction of these basic fields (both matter constituents and force carriers) with a new type of field, the Higgs scalar field, whose ground state breaks spontaneously the electroweak symmetry. The recent observation by the ATLAS and CMS experiments of a new state compatible with the properties of the Higgs boson (or the spin-0 excitation of the Higgs field) has significantly reinforced the evidences in favor of the Higgs mechanisms and the validity of the SM. However, we have also clear indications that this theory is not complete: the phenomenon of neutrino oscillations and the evidence for dark matter cannot be explained within the SM. The SM is also affected by a serious theoretical problem because of the instability of the Higgs sector under quantum corrections. We have not yet enough information to unambiguously determine how this theory should be extended; however, most realistic proposals point toward the existence of new degrees of freedom in the TeV range, possibly accessible at the high-pT experiments at the LHC. The description of quark and lepton masses in terms of the Higgs mechanism is particularly un- satisfactory since the corresponding interactions is not controlled by any symmetry principle, contrary to all other known interactions, resulting in a large number of free parameters. Beside determining quark masses, the interaction of the quarks with the Higgs is responsible for the peculiar pattern of mixing of

Astrophysical and cosmological observations strongly support the existence of Dark Matter (DM). In this study, we investigate the potential of the mono-Higgs plus missing transverse energy signature at the LHC to search for a fermionic DM candidate using the framework of Effective Field Theory. In our study, the DM interacts with the Standard Model (SM) via dimension-6 and dimension-7 effective operators involving the Higgs and the gauge bosons. Although our analysis is independent of any Ultra Violet complete dynamics of DM, such interactions can be realized in an extension of the SM where the gauge group is extended minimally by adding an extra U (1). Boosted Decision Tree (BDT) discriminators are used to estimate and optimize the signal sensitivity over the SM backgrounds, assuming an integrated luminosity of 3000 f b − 1 at s = 14 TeV at the High Luminosity phase of the LHC (HL-LHC). In the most optimistic scenario, a significance exceeding 3 σ can be achieved for relic masses ranging from 90-300 GeV, which showcases the prospects of the search at the HL-LHC. This study provides a foundation for future explorations in this direction.

The Large Hadron Collider (LHC) has confirmed the Higgs mechanism to generate mass in the Standard Model (SM), making it attractive also to consider spontaneous symmetry breaking as the origin of mass for new particles in a dark sector extension of the SM. Such a dark Higgs mechanism may in particular give mass to a dark matter candidate and to the gauge boson mediating its interactions (called dark photon). In this review, we summarize the phenomenology of the resulting dark Higgs boson and discuss the corresponding search strategies with a focus on collider experiments. We consider both the case that the dark Higgs boson is heavier than the SM Higgs boson, in which case leading constraints come from direct searches for new Higgs bosons as well missing-energy searches at the LHC, and the case that the dark Higgs boson is (potentially much) lighter than the SM Higgs boson, such that the maximum sensitivity comes from electron–positron colliders and fixed-target experiments. Of particular experimental interest for both cases is the associated production of a dark Higgs boson with a dark photon, which subsequently decays into SM fermions, dark matter particles or long-lived dark sector states. We also discuss the important role of exotic decays of the SM-like Higgs boson and complementary constraints arising from early-universe cosmology, astrophysics, and direct searches for dark matter in laboratory experiments.

This article is devoted to the processes with the participation of the t-quark. The top quarks are one of the most amazing elementary particles. Predictions of the characteristics of various interactions involving the -quark have high theoretical accuracy, as well as -quark has large production cross section which makes it a unique laboratory for testing the Standard Model and beyond. The top quark is one of the important objects in the searches for new effects. The review includes the main properties of the top quark, the complete theoretical analysis and experimental measurements of top quark processes and the possibilities of searching for manifestations of New physics beyond the Standard Model (SM). Interactions of t-quarks are described in the framework of the model-independent way and gauge-invariant methods. Another distinctive feature of study of the t-quark processes is the absence of hadrons containing -quark in nature. So there is a unique opportunity to study the fundamental properties of a  -quark without any hadronization effects. Keywords: Higgs boson, top quark, Feynman diagram, model independent and gauge invariant method, Form factor, partial width, Standard Model.

In the minimal supersymmetric standard madel, it is shown that a radiative correction of the top and stop loops gives a finite, but non-negligible contribution to Higgs scalar masses if m, ' 150-250 GeV. The upper limit to the lightest-scalar mass becomes 70-190 GeV in the range of heavy top quark. 1 The mechanism of electroweak symmetry breaking is one of the most important issues in the present particle physics_ In the standard electroweak model a funda­ mental Higgs doublet is introduceq to cause the spontaneous symmetry breaking. Supersymmetry (SUSY), eliminating all quadratic divergences, may provide a better theoretical basis to describe a fundamental Higgs boson with a relatively small mass to a high energy cutoff scale, say the Planck scale for example. I) In the minimal SUSY extension of the standard electroweak model the Higgs sector consists of two chiral superfields of Higgs doublets (/JHl and (/JH2 with opposite hypercharges. They are required to give masses for all quarks and leptons and to guarantee the ~bsence of the gauge anomaly. Five physical Higgs bosons among them survive the gauge symmetry breaking, namely, there appear two neutral scalars rpa and rpb, a neutral pseudoscalar X and a pair of charged scalars x± as physical particles. It has been, furthermore, shown by many authors 2 ) that there is at least one neutral scalar boson lighter than ZO(m<p< mzo) in the minimal SUSY model. This has strongly motivated many recent analyses of Higgs boson production at LEP energies. 3 ) In this paper, however, we stress that a radiative correctiQn gives a significant contribution to the Higgs mass term if the top quark is 8uficiently heavy as mt ~150-250 GeV. Therefore, the presence of the Higgs scalar lighter than mzo is not an inevitable prediction of the minimal SUSY standard model. Let us discuss the Higgs sedor in the minimal SUSY model. With general soft-breaking terms 4 ) of SUSY the tree-level Higgs potential is given by

micrOMEGAs5.0 : Freeze-in

In the multiverse the scale of supersymmetry breaking, $$ \widetilde{m} = {F_X}/{M_{ * }} $$ ∗, may scan and environmental constraints on the dark matter density may exclude a large range of m from the reheating temperature after inflation down to values that yield a lightest supersymmetric particle (LSP) mass of order a TeV. After selection effects, for example from the cosmological constant, the distribution for $$ \widetilde{m} $$ in the region that gives a TeV LSP may prefer larger values. A single environmental constraint from dark matter can then lead to multi-component dark matter, including both axions and the LSP, giving a TeV-scale LSP somewhat lighter than the corresponding value for single-component LSP dark matter. If supersymmetry breaking is mediated to the Standard Model sector at order X † X and higher, only squarks, sleptons and one Higgs doublet acquire masses of order $$ \widetilde{m} $$ . The gravitino mass is lighter by a factor of M ∗ /M Pl and the gaugino masses are suppressed by a further loop factor. This Spread Supersymmetry spectrum has two versions, one with Higgsino masses arising from supergravity effects of order the gravitino mass giving a wino LSP, and another with the Higgsino masses generated radiatively from gaugino masses giving a Higgsino LSP. The environmental restriction on dark matter fixes the LSP mass to the TeV domain, so that the squark and slepton masses are order 103 TeV and 106 TeV in these two schemes. We study the spectrum, dark matter and collider signals of these two versions of Spread Supersymmetry. The Higgs boson is Standard Model-like and predicted to lie in the range 110-145 GeV; monochromatic photons in cosmic rays arise from dark matter annihilations in the halo; exotic short charged tracks occur at the LHC, at least for the wino LSP; and there are the eventual possibilities of direct detection of dark matter and detailed exploration of the TeV-scale states at a future linear collider. Gauge coupling unification is at least as precise as in minimal supersymmetric theories. If supersymmetry breaking is also mediated at order X, a much less hierarchical spectrum results. The spectrum in this case is similar to that of the Minimal Supersymmetric Standard Model, but with the superpartner masses 1-2 orders of magnitude larger than those expected in natural theories.

The Higgs boson production cross-sections and decay rates depend, within the Standard Model (SM), on a single unknown parameter, the Higgs mass. In composite Higgs models where the Higgs boson emerges as a pseudo-Goldstone boson from a strongly-interacting sector, additional parameters control the Higgs properties which then deviate from the SM ones. These deviations modify the LEP and Tevatron exclusion bounds and significantly affect the searches for the Higgs boson at the LHC. In some cases, all the Higgs couplings are reduced, which results in deterioration of the Higgs searches but the deviations of the Higgs couplings can also allow for an enhancement of the gluon-fusion production channel, leading to higher statistical significances. The search in the H → γγ channel can also be substantially improved due to an enhancement of the branching fraction for the decay of the Higgs boson into a pair of photons.

Particle Physics explores the very fundamental building blocks of our universe: the nature of forces, of space and time. By exploring very energetic collisions of sub-nuclear particles with sophisticated detectors at the colliding beam accelerators (as well as others), experimental particle physicists have established the current theory known as the Standard Model (SM), one of the several theoretical postulates to explain our everyday world. It explains all phenomena known up to a very small fraction of a second after the Big Bang to a high precision; the Higgs boson, discovered recently, was the last of the particle predicted by the SM. However, many other phenomena, like existence of dark energy, dark matter, absence of anti-matter, the parameters in the SM, neutrino masses etc. are not explained by the SM. So, in order to find out what lies beyond the SM, i.e., what conditions at the earliest fractions of the first second of the universe gave rise to the SM, we constructed the Large Hadron Collider (LHC) at CERN after the Tevatron collider at Fermi National Accelerator Laboratory. Each of these projects helped us push the boundary further with new insights as we explore a yet higher energy regime. The experiments are extremely complex, and as we push the boundaries of our existing knowledge, it also requires pushing the boundaries of our technical knowhow. So, not only do we pursue humankind’s most basic intellectual pursuit of knowledge, we help develop technology that benefits today’s highly technical society. Our trained Ph.D. students become experts at fast computing, manipulation of large data volumes and databases, developing cloud computing, fast electronics, advanced detector developments, and complex interfaces in several of these areas. Many of the Particle physics Ph.D.s build their careers at various technology and computing facilities, even financial institutions use some of their skills of simulation and statistical prowess. Additionally, last but not least, today’s discoveries make for tomorrow’s practical uses of an improved life style, case in point, internet technology, fiber optics, and many such things. At The University of Iowa we are involved in the LHC experiments, ATLAS and CMS, building equipment, with calibration and maintenance, supporting the infrastructure in hardware, software and analysis as well as participating in various aspects of data analyses. Our theory group works on fundamentals of field theories and on exploration of non-accelerator high energy neutrinos and possible dark matter searches.

A search is performed for electroweak production of a vector-like top quark partner T of charge 2/3 in association with a standard model top or bottom quark, using 2.3 fb−1 of proton-proton collision data at sqrt{s}=13 TeV collected by the CMS experiment at the CERN LHC. The search targets T quarks decaying to a top quark and a Higgs boson in fully hadronic final states. For a T quark with mass above 1 TeV the daughter top quark and Higgs boson are highly Lorentz-boosted and can each appear as a single hadronic jet. Jet substructure and b tagging techniques are used to identify the top quark and Higgs boson jets, and to suppress the standard model backgrounds. An excess of events is searched for in the T quark candidate mass distribution in the data, which is found to be consistent with the expected backgrounds. Upper limits at 95% confidence level are set on the product of the single T quark production cross sections and the branching fraction mathrm{mathcal{B}}left(mathrm{T}to mathrm{t}mathrm{H}right) , and these vary between 0.31 and 0.93 pb for T quark masses in the range 1000-1800 GeV. This is the first search for single electroweak production of a vector-like T quark in fully hadronic final states.

Although the Standard Model (SM) is the best theory in describing phenomena among elementary particles, it su􏰄ers from several problems, such as the gauge hierarchy problem, origin of the electroweak symmetry breaking, non-zero neutrino mass, and no candidate of dark matter. For solving these problems, we consider minimal U(1) extension of the SM with the classically conformal invariance, where an anomaly-free U(1) gauge symmetry is introduced along with a U(1) Higgs 􏰅eld and three right- handed neutrinos (RHNs) for the seesaw mechanism generating neutrino masses. With no mass term allowed by the classically conformal invariance, the U(1) gauge symme- try is broken through the Coleman-Weinberg mechanism, which subsequently triggers the electroweak symmetry breaking. We perform parameter scan and identify regions resolving the SM Higgs vacuum instability, while satisfying the LHC Run-2 bound on the U(1) gauge boson production and the naturalness constraint. We also investigate cosmological aspects of the model. Introducing Z2 parity, one RHN being an unique parity-odd particle in the model serves as dark matter. A successful in􏰀ation sce- nario is possible by identifying the U(1) Higgs boson with in􏰀aton and introducing its non-minimal gravitational coupling. Interestingly, the LHC physics and cosmological observations are complementary narrowing down the model parameter space.

A search is performed for dark matter (DM) produced in association with a single top quark or a pair of top quarks using the data collected with the CMS detector at the LHC from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to 138 fb −1 of integrated luminosity. An excess of events with a large imbalance of transverse momentum is searched for across 0, 1 and 2 lepton final states. Novel multivariate techniques are used to take advantage of the differences in kinematic properties between the two DM production mechanisms. No significant deviations with respect to the standard model predictions are observed. The results are interpreted considering a simplified model in which the mediator is either a scalar or pseudoscalar particle and couples to top quarks and to DM fermions. Axion-like particles that are coupled to top quarks and DM fermions are also considered. Expected exclusion limits of 410 and 380 GeV for scalar and pseudoscalar mediator masses, respectively, are set at the 95% confidence level. A DM particle mass of 1 GeV is assumed, with mediator couplings to fermions and DM particles set to unity. A small signal-like excess is observed in data, with the largest local significance observed to be 1.9 standard deviations for the 150 GeV pseudoscalar mediator hypothesis. Because of this excess, mediator masses are only excluded below 310 (320) GeV for the scalar (pseudoscalar) mediator. The results are also translated into model-independent 95% confidence level upper limits on the visible cross section of DM production in association with top quarks, ranging from 1 pb to 0.02 pb.

The Physics Landscape after the Higgs Discovery at the LHC