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Dark Matter, Ancient Rocks, a Band of Higgs Bosons, and a Big Collider: or, Models of New Physics and Some Ways to Probe Them
Stockholm University, Faculty of Science, Department of Physics. (Cosmology, Particle Astrophysics and Strings ; Oskar Klein Centre)
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The past ~ 50 years have seen a remarkable success of particle physics. In the 1970s, the Standard Model was formulated and in 2012 its final ingredient, the Higgs boson, was discovered at the Large Hadron Collider (LHC). The Standard Model describes virtually all particle physics observable in the laboratory. However, despite this success, the Standard Model has a number of shortcomings. Some problems stem from its mathematical structure, most famously the hierarchy problem. Further, the Standard Model fails to describe the composition of our Universe, for example, it cannot explain the observed Dark Matter. Thus, the need for physics beyond the Standard Model is clear. A long series of experiments has been conducted to search for this new physics. Alas, these experiments came up empty handed.This thesis discusses two lines of work: 1) Arguably, the Higgs sector of the Standard Model is its least constrained part and simultaneously intimately related to many of the Standard Model's shortcomings. We discuss models extending the Higgs sector, both in a general and in a supersymmetric setting, and how they can be probed at the LHC. 2) A century after the first evidence for Dark Matter emerged, we still don't know what it is made up of. We discuss some models for Dark Matter, including axions and a particular model for Weakly Interacting Massive Particle (WIMP) Dark Matter. Then, we present some methods to search for WIMP Dark Matter, focusing on paleo-detectors, a proposed method where one would search for the traces of WIMP-nucleus interactions left in ancient minerals. 

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2019. , p. 89
Keywords [en]
particle phenomenology, supersymmetry, dark matter, higgs boson
National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
URN: urn:nbn:se:su:diva-167406ISBN: 978-91-7797-713-1 (print)ISBN: 978-91-7797-714-8 (electronic)OAI: oai:DiVA.org:su-167406DiVA, id: diva2:1299841
Public defence
2019-06-12, sal FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Accepted. Paper 8: Manuscript.

Available from: 2019-05-20 Created: 2019-03-28 Last updated: 2019-05-21Bibliographically approved
List of papers
1. NMSSM Higgs boson search strategies at the LHC and the mono-Higgs signature in particular
Open this publication in new window or tab >>NMSSM Higgs boson search strategies at the LHC and the mono-Higgs signature in particular
2017 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 95, no 11, article id 115036Article in journal (Refereed) Published
Abstract [en]

We study the collider phenomenology of the extended Higgs sector of the next-to-minimal supersymmetric Standard Model (NMSSM). The region of NMSSM parameter space favored by a 125 GeV SM-like Higgs and naturalness generically features a light Higgs and neutralino spectrum as well as a large O(1) coupling between the Higgs doublets and the NMSSM singlet fields. In such regimes, the heavier Higgs bosons can decay dominantly into lighter Higgs bosons and neutralinos. We study the prospects of observing such decays at the 13 TeV LHC, focusing on mono-Higgs signatures as probes of such regions of parameter space. We present results for the mono-Higgs reach in a framework easily applicable to other models featuring similar decay topologies. In the NMSSM, we find that the mono-Higgs channel can probe TeV scale Higgs bosons and has sensitivity even in the low tan beta, large m(A) regime that is difficult to probe in the MSSM. Unlike for many conventional Higgs searches, the reach of the mono-Higgs channel will improve significantly with the increased luminosity expected to be collected at the LHC in the ongoing and upcoming runs.

National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-145313 (URN)10.1103/PhysRevD.95.115036 (DOI)000404472700009 ()
Available from: 2017-07-25 Created: 2017-07-25 Last updated: 2019-04-25Bibliographically approved
2. Two Higgs doublets and a complex singlet: disentangling the decay topologies and associated phenomenology
Open this publication in new window or tab >>Two Higgs doublets and a complex singlet: disentangling the decay topologies and associated phenomenology
2018 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 12, article id 044Article in journal (Refereed) Published
Abstract [en]

We present a systematic study of an extension of the Standard Model (SM) with two Higgs doublets and one complex singlet (2HDM+S). In order to gain analytical understanding of the parameter space, we re-parameterize the 27 parameters in the Lagrangian by quantities more closely related to physical observables: physical masses, mixing angles, trilinear and quadratic couplings, and vacuum expectation values. Embedding the 125 GeV SM-like Higgs boson observed at the LHC places stringent constraints on the parameter space. In particular, the mixing of the SM-like interaction state with the remaining states is severely constrained, requiring approximate alignment without decoupling in the region of parameter space where the additional Higgs bosons are light enough to be accessible at the LHC. In contrast to 2HDM models, large branching ratios of the heavy Higgs bosons into two lighter Higgs bosons or a light Higgs and a Z boson, so-called Higgs cascade decays, are ubiquitous in the 2HDM+S. Using currently available limits, future projections, and our own collider simulations, we show that combining different final states arising from Higgs cascades would allow to probe most of the interesting region of parameter space with Higgs boson masses up to 1 TeV at the LHC with L = 3000 fb(-1) of data.

Keywords
Beyond Standard Model, Higgs Physics
National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-163533 (URN)10.1007/JHEP12(2018)044 (DOI)000453294300007 ()
Available from: 2019-01-08 Created: 2019-01-08 Last updated: 2019-04-25Bibliographically approved
3. The NMSSM is within reach of the LHC: mass correlations & decay signatures
Open this publication in new window or tab >>The NMSSM is within reach of the LHC: mass correlations & decay signatures
2019 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 4, article id 011Article in journal (Refereed) Published
Abstract [en]

The Next-to-Minimal Supersymmetric Standard Model (NMSSM), the singlet extension of the MSSM which fixes many of the MSSM's shortcomings, is shown to be within reach of the upcoming runs of the Large Hadron Collider (LHC). A systematic treatment of the various Higgs decay channels and their interplay has been lacking due to the seemingly large number of free parameters in the NMSSM's Higgs sector. We demonstrate that due to the SM-like nature of the observed Higgs boson, the NMSSM's Higgs and neutralino sectors have highly correlated masses and couplings and can effectively be described by four physically intuitive parameters: the physical masses of the two CP-odd states and their mixing angle, and tan , which plays a minor role. The heavy Higgs bosons in the NMSSM have large branching ratios into pairs of lighter Higgs bosons or a light Higgs and a Z boson. Search channels arising via these Higgs cascades are unique to models like the NMSSM with a Higgs sector larger than that of the MSSM. In order to cover as much of the NMSSM parameter space as possible, one must combine conventional search strategies employing decays of the additional Higgs bosons into pairs of SM particles with Higgs cascade channels. We demonstrate that such a combination would allow a significant fraction of the viable NMSSM parameter space containing additional Higgs bosons with masses below 1 TeV to be probed at future runs of the LHC.

Keywords
Supersymmetry Phenomenology
National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-168288 (URN)10.1007/JHEP04(2019)011 (DOI)000463637400002 ()
Available from: 2019-04-30 Created: 2019-04-30 Last updated: 2019-05-21Bibliographically approved
4. Higgs portals for thermal Dark Matter. EFT perspectives and the NMSSM
Open this publication in new window or tab >>Higgs portals for thermal Dark Matter. EFT perspectives and the NMSSM
2018 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 4, article id 069Article in journal (Refereed) Published
Abstract [en]

We analyze a low energy effective model of Dark Matter in which the thermal relic density is provided by a singlet Majorana fermion which interacts with the Higgs fields via higher dimensional operators. Direct detection signatures may be reduced if blind spot solutions exist, which naturally appear in models with extended Higgs sectors. Explicit mass terms for the Majorana fermion can be forbidden by a Z(3) symmetry, which in addition leads to a reduction of the number of higher dimensional operators. Moreover, a weak scale mass for the Majorana fermion is naturally obtained from the vacuum expectation value of a scalar singlet field. The proper relic density may be obtained by the s-channel interchange of Higgs and gauge bosons, with the longitudinal mode of the Z boson (the neutral Goldstone mode) playing a relevant role in the annihilation process. This model shares many properties with the Next-to-Minimal Supersymmetric extension of the Standard Model (NMSSM) with light singlinos and heavy scalar and gauge superpartners. In order to test the validity of the low energy effective field theory, we compare its predictions with those of the ultraviolet complete NMSSM. Extending our framework to include Z(3) neutral Majorana fermions, analogous to the bino in the NMSSM, we find the appearance of a new bino-singlino well tempered Dark Matter region.

Keywords
Cosmology of Theories beyond the SM, Beyond Standard Model, Effective Field Theories, Supersymmetric Effective Theories
National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-155905 (URN)10.1007/JHEP04(2018)069 (DOI)000430130300001 ()
Available from: 2018-04-30 Created: 2018-04-30 Last updated: 2019-04-25Bibliographically approved
5. Dark matter capture, subdominant WIMPs, and neutrino observatories
Open this publication in new window or tab >>Dark matter capture, subdominant WIMPs, and neutrino observatories
2017 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 95, no 4, article id 043007Article in journal (Refereed) Published
Abstract [en]

Weakly interacting massive particles (WIMPs), which are among the best motivated dark matter (DM) candidates, could make up all or only a fraction of the total DM budget. We consider a scenario in which WIMPs are a subdominant DM component; such a scenario would affect both current direct and indirect bounds on the WIMP-nucleon scattering cross section. In this paper we focus on indirect searches for the neutrino flux produced by annihilation of subdominant WIMPs captured by the Sun or the Earth via either spin-dependent or spin-independent scattering. We derive the annihilation rate and the expected neutrino flux at neutrino observatories. In our computation, we include an updated chemical composition of the Earth with respect to the previous literature, leading to an increase of the Earth's capture rate for spin-dependent scattering by a factor of 3. Results are compared with current bounds from Super-Kamiokande and IceCube. We discuss the scaling of bounds from both direct and indirect detection methods with the WIMP abundance.

National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-142494 (URN)10.1103/PhysRevD.95.043007 (DOI)000394664300001 ()
Available from: 2017-05-12 Created: 2017-05-12 Last updated: 2019-04-25Bibliographically approved
6. Dilute and dense axion stars
Open this publication in new window or tab >>Dilute and dense axion stars
Show others...
2018 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 777, p. 64-72Article in journal (Refereed) Published
Abstract [en]

Axion stars are hypothetical objects formed of axions, obtained as localized and coherently oscillating solutions to their classical equation of motion. Depending on the value of the field amplitude at the core vertical bar theta(0)vertical bar vertical bar theta(r = 0)vertical bar, the equilibrium of the system arises from the balance of the kinetic pressure and either self-gravity or axion self-interactions. Starting from a general relativistic framework, we obtain the set of equations describing the configuration of the axion star, which we solve as a function of vertical bar theta(0)vertical bar. For small vertical bar theta(0)vertical bar less than or similar to 1, we reproduce results previously obtained in the literature, and we provide arguments for the stability of such configurations in terms of first principles. We compare qualitative analytical results with a numerical calculation. For large amplitudes vertical bar theta(0)vertical bar greater than or similar to 1, the axion field probes the full non-harmonic QCD chiral potential and the axion star enters the densebranch. Our numerical solutions show that in this latter regime the axions are relativistic, and that one should not use a single frequency approximation, as previously applied in the literature. We employ a multi-harmonic expansion to solve the relativistic equation for the axion field in the star, and demonstrate that higher modes cannot be neglected in the dense regime. We interpret the solutions in the dense regime as pseudo-breathers, and show that the life-time of such configurations is much smaller than any cosmological time scale.

National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-153759 (URN)10.1016/j.physletb.2017.12.010 (DOI)000423930700006 ()
Available from: 2018-03-27 Created: 2018-03-27 Last updated: 2019-04-25Bibliographically approved
7. Dark Matter implications of DAMA/LIBRA-phase2 results
Open this publication in new window or tab >>Dark Matter implications of DAMA/LIBRA-phase2 results
2019 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 789, p. 262-269Article in journal (Refereed) Published
Abstract [en]

Recently, the DAMA/LIBRA collaboration released updated results from their search for the annual modulation signal from Dark Matter (DM) scattering in the detector. Besides approximately doubling the exposure of the DAMA/LIBRA data set, the updated photomultiplier tubes of the experiment allow a lower recoil energy threshold of I keV electron equivalent compared to the previous threshold of 2 keV electron equivalent. We study the compatibility of the observed modulation signal with DM scattering. Due to a conspiracy of multiple effects, the new data at low recoil energies is very powerful for testing the DM hypothesis. We find that canonical (isospin conserving) spin-independent DM-nucleon interactions are no longer a good fit to the observed modulation signal in the standard halo model. The canonical spin independent case is disfavored by the new data, with best fit points of a DM mass of similar to 8 GeV, disfavored by 5.2 sigma, or a mass of similar to 54GeV, disfavored by 2.5 sigma. Allowing for isospin violating spin independent interactions, we find a region with a good fit to the data with suppressed effective couplings to iodine for DM masses of similar to 10 GeV. We also consider spin-dependent DM-nucleon interactions, which yield good fits for similar DM masses of similar to 10 GeV or similar to 45 GeV.

National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-166722 (URN)10.1016/j.physletb.2018.12.036 (DOI)000457165400036 ()
Available from: 2019-03-18 Created: 2019-03-18 Last updated: 2019-04-25Bibliographically approved
8. Searching for Dark Matter with Paleo-Detectors
Open this publication in new window or tab >>Searching for Dark Matter with Paleo-Detectors
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

A large experimental program is underway to extend the sensitivity of direct detection experiments, searching for interactions of Dark Matter with nuclei, down to the neutrino floor. However, such experiments are becoming increasingly difficult and costly due to the large target masses and exquisite background rejection needed for the necessary improvements in sensitivity. We investigate an alternative approach to the detection of Dark Matter--nucleon interactions: Searching for the persistent traces left by Dark Matter scattering in ancient minerals obtained from much deeper than current underground laboratories. We estimate the sensitivity of paleo-detectors, which extends far beyond current upper limits for a wide range of Dark Matter masses.

National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-167401 (URN)
Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-04-25
9. Paleo-detectors: Searching for Dark Matter with Ancient Minerals
Open this publication in new window or tab >>Paleo-detectors: Searching for Dark Matter with Ancient Minerals
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2019 (English)In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 99, no 4, article id 043014Article in journal (Refereed) Published
Abstract [en]

We explore paleo-detectors as an approach to the direct detection of weakly interacting massive particle (WIMP) dark matter radically different from conventional detectors. Instead of instrumenting a (large) target mass in a laboratory in order to observe WIMP-induced nuclear recoils in real time, the approach is to examine ancient minerals for traces of WIMP-nucleus interactions recorded over timescales as large as 1 Gyr. Here, we discuss the paleo-detector proposal in detail, including background sources and possible target materials. In order to suppress backgrounds induced by radioactive contaminants such as uranium, we propose to use minerals found in marine evaporites or in ultrabasic rocks. We estimate the sensitivity of paleo-detectors to spin-independent and spin-dependent WIMP-nucleus interactions. The sensitivity to low-mass WIMPs with masses mχ≲10  GeV extends to WIMP-nucleon cross sections many orders of magnitude smaller than current upper limits. For heavier WIMPs with masses mχ≳30  GeV cross sections a factor of a few to ∼100 smaller than current upper limits can be probed by paleo-detectors.

National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-167403 (URN)10.1103/PhysRevD.99.043014 (DOI)000459912000002 ()
Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-04-25Bibliographically approved
10. Digging for dark matter: Spectral analysis and discovery potential of paleo-detectors
Open this publication in new window or tab >>Digging for dark matter: Spectral analysis and discovery potential of paleo-detectors
Show others...
2019 (English)In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 99, no 4, article id 043541Article in journal (Refereed) Published
Abstract [en]

Paleo-detectors are a recently proposed method for the direct detection of dark matter (DM). In such detectors, one would search for the persistent damage features left by DM–nucleus interactions in ancient minerals. Initial sensitivity projections have shown that paleo-detectors could probe much of the remaining weakly interacting massive particle (WIMP) parameter space. In this paper, we improve upon the cut-and-count approach previously used to estimate the sensitivity by performing a full spectral analysis of the background- and DM-induced signal spectra. We consider two scenarios for the systematic errors on the background spectra: (i) systematic errors on the normalization only, and (ii) systematic errors on the shape of the backgrounds. We find that the projected sensitivity is rather robust to imperfect knowledge of the backgrounds. Finally, we study how well the parameters of the true WIMP model could be reconstructed in the hypothetical case of a WIMP discovery.

National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-167405 (URN)10.1103/PhysRevD.99.043541 (DOI)000459913000001 ()
Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-04-25Bibliographically approved

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