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Alternatives to Standard Tev-Scale New Physics Scenarios

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Alternatives to Standard Tev-Scale New Physics Scenarios Alternatives to standard TeV-scale New Physics scenarios Stéphane Lavignac (IPhT Saclay) • introduction • usual prejudices about New Physics • split supersymmetry and high-scale supersymmetry • minimal scenarios with sterile neutrinos « Le futur de la Physique des Particules » Journée de la Division Particules et Champs de la SFP LPNHE, Paris, 23 janvier 2015 Introduction New Physics expected because the Standard Model is incomplete: Unexplained observational facts: • neutrino masses • dark matter (DM) • matter-antimatter asymmetry (BAU) • inflation somewhat different in nature • cosmological constant } involve also gravity Theoretical problems: • strong CP problem • origin of electroweak symmetry breaking (EWSB) • large number of parameters, mass hierarchies • incomplete unification of forces • hierarchy problem (in the presence of ⇤ NP M W ) The hierarchy problem has often been used as a guide to discriminate among theories beyond the SM, favouring supersymmetry, extra dimensions and composite Higgs models These theories are now strongly challenged by negative search results from colliders and dark matter experiments → emergence of alternative scenarios in which naturalness is no longer required, such as: • split supersymmetry • high-scale supersymmetry • scenarios with superheavy sterile neutrinos (seesaw) • scenarios with keV/GeV sterile neutrinos, such as the νMSM 18 C. Grojean be. The SM particles give unnaturally large corrections to the Higgs mass: they destabilize the Higgs vev and tend to push18 it towards the UV cutoff ofC. the Grojean SM. Some precise adjustment (fine-tuning)18 between the bare massC. Grojeanand the one-loop correction is needed to maintain the vevbe.of the The Higgs SM particles around give the unnaturally weak scale: large take corrections to the Higgs mass: they be. The SM particles give unnaturally large corrections to the Higgs mass: they two large numbers, naturally their sum/differencedestabilize the will Higgs be ovevfthesameorderun-and tend to push it towards the UV cutoff of the SM. destabilizeSome the Higgs precisevevUsual adjustmentand tend to (fine-tuning) pushprejudices it towards between the UV the cutoffabout bare of mass the SM.Newand the one-loop Physics less these numbers are almost equal up to several significant digits (see [17] for Some precisecorrection adjustment is needed (fine-tuning) to maintain between the vev the bareof the mass Higgsand around the one-loop the weak scale: take arecentestimateoftheamountoffine-tuningwithintheSMancorrectiontwo is needed large numbers,to maintain naturally the vevdvariousmodelsof their the Higgs sum/difference around the weak will be scale: ofthesameorderun- take BSM). two largeless numbers, these naturally numbers their are almost sum/difference equal up will to be several ofthesameorderun- significant digits (see [17] for less1) these should numbers arebe almost natural equal up ⇒ to several avoid significant the digitshierarchy (see [17] for problem arecentestimateoftheamountoffine-tuningwithintheSMandvariousmodels arecentestimateoftheamountoffine-tuningwithintheSMandvariousmodels BSM). BSM).Origin of the problem: radiative corrections to the scalar mass parameter = 2 c 2 δmH 2 M = = ⇠ 16⇡ Fig. 6. One loop corrections to the Higgs mass. The three diagrams are quadratically divergent and make the Higgs mass highly UV sensitive. Fig. 6. OneFig. loop 6. corrections One loop to corrections the Higgs mass. to the The Higgs three mass. diagrams The are three quadratically diagrams aredivergent quadratically and divergent and makeAny the Higgs heavy mass highly particle UV sensitive. with mass M M W coupling to the Higgs boson will destabilizemake the Higgs the mass weak highly UV scale sensitive. The hierarchy problem is a generic technical problem in any theory involving The hierarchyThe problemhierarchy is problem a generic is technical a generic problem technical in any problem theory involving in any theory involving some light scalar fields. some→ lightthe scalar hierarchy fields. M W M must be ensured by a fine-tuning some light scalar fields. In the study of any theory beyondIn the the study Standard of any theory Model, beyond one need the⌧ Standardstobeableto Model, one needstobeableto In the study of any theory beyond the Standard Model, one needstobeableto quickly estimate the quadraticallyquickly divergent estimate corrections the quadraticallyto the divergent scalar corrections potentials.to the scalar potentials. This quicklycriterion estimate favours the quadratically theories divergent like corrections supersymmetry,to the scalar potentials. extra-dimensions (ADD One can calculate explicitly someOne Feynman can calculate diagrams explicitly or some more Feynman conveniently diagrams rely or more conveniently rely on the computationOne can calculate of the Coleman–Weinberg explicitly some Feynman potential [18].diagramsAt one-loop or more this conveniently rely k⇡rc on the computation of the Coleman–Weinbergmodel where potential M [18]. At1 TeV one-loop , RS this model in which M W /M Pl = e − ) and effective potentialon the computation for a scalar( fieldd of) the⇠φ is Coleman–Weinberg given by potential [18]. At one-loop this effective potential for a scalar fieldcompositeφ iseffective given by potentialHiggs formodels a scalar field (solveφ is given the by little hierarchy problem) 4 d kE 2 2 4 V (φ)= 4 STr ln(k4 E +M (φ)), (2.44) d kE 2 2 2(2π) d kE 2 2 V (φ)= STr ln(k +M!(φV))(φ,)= (2.44)STr ln(kE +M (φ)), (2.44) 2(2π)4 E 2(2π)4 ! where the supertrace, i.e. the trace with! an extra minus sign for the fermionic degrees ofwhere freedom, the is supertrace, over all thei.e. particlesthe trace that acquire with an a extra mass whenminusφ signis away for the fermionic where the supertrace, i.e. the trace with an extra minus sign for4 the fermionic from the origin.degrees After of freedom, integrating is over overd allkE the,weget particles that acquire a mass when φ is away degrees of freedom, is over all the particlesfrom thethat origin. acquire After a m integratingass when overφ isd away4k ,weget 4 E from the origin. After integrating over d kE4 ,weget 2 2 Λ Λ 2 1 4 M (φ) V = 2 STr 1 + 2 STr M (φ)+ 2 STr M (φ) ln 2 , −128π 4 64π 2 64π Λ 2 Λ Λ 2 1 4 M (φ) 4 2 V = 2 STr 1 + 2 STr2 M (φ)+ 2 STr M (φ) ln 2 , Λ Λ 2 −1128π 4 64πM (φ) 64π Λ V = 2 STr 1 + 2whereSTr M we( easilyφ)+ read off2 STr the quadratically M (φ) ln divergent2 , corrections to the scalar po- −128π 64π tential. Let us look64 explicitlyπ at the case of theΛ Higgs in the SM. The only things where we easily read off the quadratically divergent corrections to the scalar po- where we easily read off the quadraticallytential. divergent Let us look correc explicitlytions to at the the scalar case of po- the Higgs in the SM. The only things tential. Let us look explicitly at the case of the Higgs in the SM. The only things 2) the dark matter particle is a Weakly Interacting Massive Particle Relic abundance determined by freeze-out: ⌦χ 1/ σAv / h i Turner] [Kolb, weakly interacting: σ ↵2 /m2 A ⇠ w χ ⌦ 0.1 for m (0.1 1) TeV ) χ ⇠ χ ⇠ − i.e. close to the scale suggested by the hierarchy problem “ WIMP miracle ” Examples: neutralino (if LSP) in supersymmetric models, lightest Kaluza-Klein particle (LKP) in universal extra dimension scenarios, ... 3) neutrino masses are generated from the seesaw mechanism Easily accommodated in any scenario: just add RH neutrinos with a large Majorana mass term and a Dirac coupling to the SM neutrinos ⇒ naturally generates small SM neutrino masses 4) strong CP problem ignored, or solved by the axion ✓ The QCD Lagrangian a priori contains a CP-odd term G G˜µ⌫ 16⇡2 µ⌫ which induces a (large) neutron EDM exp 25 10 d < 0.29 10− ecm ✓ 10− n ⇥ ) . A natural solution involves the pseudo-Goldstone boson of a spontaneously broken, anomalous global symmetry such as the Peccei-Quinn symmetry (the axion a), which drives dynamically θ to zero The axion gets a sub-eV mass from QCD instantons and can constitute part or all of the CDM density 5) the cosmological constant problem is solved somehow If dark energy interpreted as a cosmological constant, observations require 48 4 120 4 ⇤ = V 10− GeV 10− M 0 ⇡ ⇡ Pl → largest fine-tuning in nature. Even if solved, any phase transition (Susy, EW, 4 QCD) occurring at T = ⇤ PT will contribute as ⇤ PT to the vacuum energy Not a problem for the SM alone, but for SM + gravity Among the various possibilities for BSM physics, (low-energy) supersymmetry emerged as the preferred option because: • automatically solves the hierarchy problem • a neutralino LSP is a suitable DM candidate • allows gauge coupling unification • radiative electroweak symmetry breaking possible • cosmological constant problem softened • may be inherited from string theory Extra dimensions also address the hierarchy problem and provide new DM candidates as well as new ideas for EWSB, the flavour problem or the cosmological constant problem Composite Higgs models solve the little hierarchy problem and feature a dynamical origin for EWSB, provide also new ideas for the flavour problem and DM These theories are now strongly challenged by negative search results from the LHC and from dark matter experiments Supersymmetry gluino, first 2 gen. squarks: m> (1 1 .5) TeV (depending on model) − Higgs mass constraint: 3g2m4 sin2 β m2 X X2 m2 m2 cos2 2β + t ln S + t 1 t h Z 8⇡2m2 m2 m2 − 12m2 W ✓ t ◆ S ✓ s ◆ ⇒ m h = 125 GeV requires multi-TeV stops or maximal stop mixing These lower bounds imply large corrections to the Higgs potential, hence a strong (sub-percent) fine-tuning: 3y2 ⇤2 δm2 t m2 ln Hu ⇠ 16⇡2 S m2 ✓ S ◆ Extra dimensions RS gravitons: m & 2 TeV Large ED (ADD): M(d) & several TeV Composite Higgs models top partners: m (500 800) GeV & − (heavier top partners imply a stronger fine-tuning) / Nuclear Physics B Proceedings Supplement 00 (2014) 1–6 4 miss -1 CMS Preliminary e + ET L dt = 20 fb s = 8 TeV 7 ∫ ity between the collider and direct searches.
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