16 research outputs found
Higgs boson and vacuum stability in models with extended scalar sector
In this dissertation Two-Higgs-Doublet Models (2HDMs) with a Z2-symmetric scalar potential are studied from different perspectives. Two kinds of models, which differ by the choice of the vacuum state, are analysed. One of them is the so-called 2HDM (mixed) which breaks the symmetry of the potential by non-zero vacuum expectation values (VEVs) of the neutral components of the two scalar doublets. The other one, the exactly Z2-symmetric Inert Doublet Model (IDM) with only one non-vanishing VEV, is of central interest to this work. It contains a SM-like Higgs boson and a candidate for the dark matter (DM) particle.
The first part of this thesis is devoted to the analysis of the allowed parameter space of the studied 2HDMs. The models are subject to a number of constrains, such as: positivity of the potential, stability of the vacuum state, perturbative unitarity, electroweak precision tests and the LEP bounds. We also take into account the fact that the scalar discovered at the LHC is a SM-like Higgs boson with mass around 125 GeV. We present the allowed regions in the parameter space for the parameters of the potential and the physical masses. For the 2HDM (mixed), within a scenario where the lightest CP-even scalar plays a role of the SM-like Higgs particle, we find a strong bound on the parameter tan尾, which is independent of the type of Yukawa interactions. In the IDM we derive an upper bound on the mass parameter of the potential which is based on the condition for the stability of the vacuum and excludes a phenomenologically interesting part of the parameter space.
In the second part of the present dissertation, constraints on the properties of the new scalars of the IDM, based on the experimental results for the Higgs particle, are analysed. First of all, we study the Higgs diphoton decay. We show, that the additional scalars (in particular the charged scalar and the DM candidate) can affect the observed signal strength of this decay. From this fact, we infer strong upper and lower limits on the masses of these particles. Next, the decay of the Higgs to a Z boson and a photon is analysed. We demonstrate that the correlation between the diphoton and Z纬 signal strength is positive, which gives a possible experimental probe of the IDM. Furthermore, we study the invisible and total decay widths of the Higgs boson and infer constraints on the DM particle and its coupling to the Higgs particle. In the following, the Higgs results are combined with the DM data. We derive constraints and exclusions for different possible DM scenarios, proving the idea of combining different sources of results very fruitful. Interestingly, the results of this combination, when translated to the parameters probed by the direct detection experiments, give constraints which are comparable or even stronger than the results of the dedicated searches.
In the final part of the present dissertation, the issue of vacuum stability is studied, in particular, the influence of the additional scalars on this problem. Two distinct approaches are adopted. First, the additional scalars of the IDM are assumed to be heavy, and thus they contribute to the effective potential only through loop corrections. We demonstrate that the heavy inert scalars can change the structure of the effective potential, introducing a new minimum which is deeper than the SM one and this way they can destabilise the vacuum state. In addition, the regions where destabilisation of the vacuum may occur are confronted with theoretical and experimental constraints, and we prove that the IDM, in the valid part of the parameter space, is free from the threat of vacuum instability. The other approach to the issue of vacuum stability adopted in this thesis admits all of the scalar fields in the effective potential, and thus allows the study of the coexistence of different minima. We show that the inert minimum can coexist with an inert-like one at one-loop level in a vaster region of the parameter space than at tree level. Moreover, we demonstrate that the loop corrections may invert the ordering of the minima, i.e. a tree-level global minimum may, in certain cases, become a local one at one-loop level. This shows the importance of beyond-tree-level analysis of the issue of vacuum stability.Niniejsza dysertacja po艣wi臋cona jest badaniu modeli z dwoma dubletami p贸l Higgsa (ang. Two-Higgs- Doublet Model, 2HDM) opisywanych potencja艂em skalarnym z symetri膮 typu Z2. Analizowane s膮 dwa rodzaje modeli 2HDM r贸偶ni膮ce si臋 wyborem stanu pr贸偶ni. Pierwszy z nich to tzw. 2HDM (mixed), kt贸ry 艂amie symetri臋 potencja艂u, gdy偶 w stanie pr贸偶ni neutralne sk艂adowe obu skalarnych dublet贸w uzyskuj膮 niezerow膮 pr贸偶niow膮 warto艣膰 oczekiwan膮. Drugi, model z biernym dubletem p贸l skalarnych (ang. Inert Doublet Model, IDM ) posiadaj膮cy jedn膮 niezerow膮 pr贸偶niow膮 warto艣膰 oczekiwan膮 i zachowuj膮cy tym samym symetri臋 potencja艂u, jest g艂贸wnym przedmiotem niniejszej pracy. Zawiera on bozon Higgsa o w艂asno艣ciach zbli偶onych do w艂asno艣ci bozonu Higgsa z Modelu Standardowego (ang. Standard Model, SM ) oraz kandydatk臋 na cz膮stk臋 ciemnej materii.
Pierwsza cz臋艣膰 niniejszej pracy jest po艣wi臋cona analizie przestrzeni parametr贸w badanych modeli 2HDM. Modele te s膮 ograniczane przez rozmaite warunki i pomiary takie jak: dodatnio艣膰 potencja艂u, stabilno艣膰 stanu pr贸偶ni, perturbacyjna unitarno艣膰, precyzyjne dane elektros艂abe oraz ograniczenia z akceleratora LEP. Ponadto bierzemy pod uwag臋 fakt, 偶e cz膮stka skalarna odkryta w LHC ma w艂asno艣ci standardowego bozonu Higgsa oraz mas臋 oko艂o 125 GeV. Dozwolone obszary s膮 przedstawione w przestrzeni parametr贸w potencja艂u oraz fizycznych mas cz膮stek. W modelu 2HDM (mixed), w przypadku gdy najl偶ejsza cz膮stka skalarna o do- datniej parzysto艣ci CP pe艂ni rol臋 bozonu Higgsa, prezentujemy nowe silne ograniczenie na parametr tan尾, niezale偶nie od typu oddzia艂ywa艅 Yukawy. W modelu IDM, w oparciu o warunek stabilno艣ci pr贸偶ni, wypro- wadzamy ograniczenie na parametr masowy potencja艂u, kt贸re wyklucza interesuj膮cy z fenomenologicznego punktu widzenia obszar przestrzeni parametr贸w.
W drugiej cz臋艣ci niniejszej dysertacji w oparciu o dane eksperymentalne dotycz膮ce bozonu Higgsa, wy- prowadzamy ograniczenia na mo偶liwe w艂asno艣ci nowych cz膮stek skalarnych w IDM. W pierwszej kolejno艣ci analizowany jest rozpad bozonu Higgsa na dwa fotony. Pokazujemy, 偶e dodatkowe skalary, w szczeg贸lno艣ci cz膮stka na艂adowana oraz kandydatka na cz膮stk臋 ciemnej materii, mog膮 znacz膮co wp艂ywa膰 na si艂臋 sygna艂u dla tego rozpadu. Z tego faktu wyprowadzamy silne ograniczenia na masy tych cz膮stek. Nast臋pnie, analizowany jest rozpad bozonu Higgsa na bozon Z oraz foton. Pokazujemy, 偶e korelacja mi臋dzy si艂ami sygna艂u w tym kanale oraz kanale dwufotonowym jest pozytywna, co stwarza mo偶liwo艣膰 poddania IDM eksperymentalnej weryfikacji. Ponadto, badamy stosunek rozga艂臋zie艅 rozpadu bozonu Higgsa na cz膮stki niewidzialne oraz jego ca艂kowit膮 szeroko艣膰 rozpadu, co pozwala na wyprowadzenie ogranicze艅 na mas臋 cz膮stki ciemnej materii oraz jej sprz臋偶enie do bozonu Higgsa. W dalszej cz臋艣ci wyniki dotycz膮ce bozonu Higgsa s膮 po艂膮czone z danymi do- tycz膮cymi ciemnej materii. Wyprowadzamy istotne ograniczenia i wykluczenia dotycz膮ce r贸偶nych mo偶liwych scenariuszy istnienia ciemnej materii, pokazuj膮c tym samym, 偶e 艂膮czenie r贸偶nych 藕r贸de艂 danych mo偶e by膰 niezwykle owocne. Nasze ograniczenia wynikaj膮ce z tej analizy przet艂umaczone na ograniczenie parametr贸w pr贸bkowanych przez eksperymenty bezpo艣redniej detekcji ciemnej materii okazuj膮 si臋 by膰 por贸wnywalne lub nawet silniejsze od wynik贸w tych dedykowanych poszukiwa艅 ciemnej materii.
W ostatniej cz臋艣ci niniejszej pracy analizowany jest problem stabilno艣ci stanu pr贸偶ni, w szczeg贸lno艣ci wp艂yw jaki maj膮 na niego dodatkowe cz膮stki skalarne. Badamy to zagadnienie na dwa r贸偶ne sposoby. W ra- mach pierwszego podej艣cia zak艂adamy, 偶e dodatkowe skalary s膮 ci臋偶kie i w zwi膮zku z tym mog膮 dawa膰 wk艂ad do potencja艂u efektywnego jedynie poprzez efekty p臋tlowe. Pokazujemy, 偶e dodatkowe skalary mog膮 zmo- dyfikowa膰 struktur臋 potencja艂u efektywnego i zdestabilizowa膰 stan pr贸偶ni, wprowadzaj膮c dodatkowe g艂臋bsze minimum. Dodatkowo, konfrontuj膮c obszary parametr贸w, w kt贸rych mo偶liwa jest destabilizacja pr贸偶ni z ograniczeniami teoretycznymi i do艣wiadczalnymi, pokazujemy, 偶e w IDM taki scenariusz nie jest mo偶liwy. Drugie podej艣cie do problemu stabilno艣ci pr贸偶ni stosowane w niniejszej pracy pozwala na obecno艣膰 wszyst- kich p贸l skalarnych w potencjale efektywnym, stwarzaj膮c tym samym mo偶liwo艣膰 zbadania wsp贸艂istnienia r贸偶nych typ贸w minim贸w. Pokazujemy, 偶e minima typu inert oraz inert-like mog膮 wsp贸艂istnie膰 na poziomie p臋tlowym, w szerszym zakresie parametr贸w ni偶 na poziomie drzewowym. Co wi臋cej, pokazujemy, 偶e po- prawki p臋tlowe mog膮 odwr贸ci膰 uporz膮dkowanie pr贸偶ni, tzn. drzewowe minimum globalne mo偶e sta膰 si臋 na poziomie p臋tlowym minimum lokalnym. To pokazuje jak istotne mo偶e by膰 wyj艣cie poza poziom drzewowy w analizie stabilno艣ci pr贸偶ni
Scale-Invariant Model for Gravitational Waves and Dark Matter
We have conducted a revised analysis of the first-order phase transition that
is associated with symmetry breaking in a classically scale-invariant model
that has been extended with a new gauge group. By incorporating recent
developments in the understanding of supercooled phase transitions, we were
able to calculate all of its features and significantly limit the parameter
space. We were also able to predict the gravitational wave spectra generated
during this phase transition and found that this model is well-testable with
LISA. Additionally, we have made predictions regarding the relic dark matter
abundance. Our predictions are consistent with observations but only within a
narrow part of the parameter space. We have placed significant constraints on
the supercool dark matter scenario by improving the description of percolation
and reheating after the phase transition, as well as including the running of
couplings. Finally, we have also analyzed the renormalization-scale dependence
of our results.Comment: 18+9 pages, 9 figures, invited talk given at CORFU2022, summarizing
the results of arXiv:2210.0707
Erratum: Yukawa independent constraints for two-Higgs-doublet models with a 125聽GeV Higgs boson [Phys. Rev. D 88
Conformal model for gravitational waves and dark matter: a status update
Abstract We present an updated analysis of the first-order phase transition associated with symmetry breaking in the early Universe in a classically scale-invariant model extended with a new SU(2) gauge group. Including recent developments in understanding supercooled phase transitions, we compute all of its characteristics and significantly constrain the parameter space. We then predict gravitational wave spectra generated during this phase transition and by computing the signal-to-noise ratio we conclude that this model is well-testable (and falsifiable) with LISA. We also provide predictions for the relic dark matter abundance. It is consistent with observations in a rather narrow part of the parameter space. We strongly constrain the so-called supercool dark matter scenario based on an improved description of percolation and reheating after the phase transition as well as the inclusion of the running of couplings. Finally, we devote attention to the renormalisation-scale dependence of the results. Even though our main results are obtained with the use of renormalisation-group improved effective potential, we also perform a fixed-scale analysis which proves that the dependence on the scale is not only qualitative but also quantitative
Systematic analysis of radiative symmetry breaking in models with extended scalar sector
Radiative symmetry breaking (RSB) is a theoretically appealing framework for the generation of mass scales through quantum effects. It can be successfully implemented in models with extended scalar and gauge sectors. We provide a systematic analysis of RSB in such models: we review the common approximative methods of studying RSB, emphasising their limits of applicability and discuss the relevance of the relative magnitudes of tree-level and loop contributions as well as the dependence of the results on the renormalisation scale. The general considerations are exemplified within the context of the conformal Standard Model extended with a scalar doublet of a new SU(2)X gauge group, the so-called SU(2)cSM. We show that various perturbative methods of studying RSB may yield significantly different results due to renormalisation-scale dependence. Implementing the renormalisation-group (RG) improvement method recently developed in ref. [1], which is well-suited for multi-scale models, we argue that the use of the RG improved effective potential can alleviate this scale dependence providing more reliable results
Gravitational waves from supercooled phase transitions : dimensional transmutation meets dimensional reduction
Models with radiative symmetry breaking typically feature strongly supercooled first-order phase transitions, which result in an observable stochastic gravitational wave background. In this work, we analyse the role of higher-order thermal corrections for these transitions, applying high-temperature dimensional reduction to a theory with dimensional transmutation. In particular, we study to what extent high-temperature effective field theories (3D EFT) can be used. We find that despite significant supercooling down from the critical temperature, the high-temperature expansion for the bubble nucleation rate can be applied using the 3D EFT framework, and we point out challenges in the EFT description. We compare our findings to previous studies and find that the next-to-leading order corrections obtained in this work have a significant effect on the predictions for GW observables, motivating a further exploration of higher-order thermal effects.Peer reviewe