Publications (74)292.42 Total impact
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ABSTRACT: After the Higgs boson discovery, it is established that the Higgs mechanism explains electroweak symmetry breaking and generates the masses of all particles in the Standard Model, with the possible exception of neutrino masses. The hierarchies among fermion masses and mixing angles remain however unexplained. We propose a new class of two Higgs doublet models in which a flavor symmetry broken at the electroweak scale addresses this problem. The models are strongly constrained by electroweak precision tests and the fact that they produce modifications to Higgs couplings and flavor changing neutral currents; they are also constrained by collider searches for extra scalar bosons. The surviving models are very predictive, implying unavoidable new physics signals at the CERN Large Hadron Collider, e.g. extra Higgs Bosons with masses $M < 700$ GeV.  [Show abstract] [Hide abstract]
ABSTRACT: The NexttoMinimal Supersymmetric extension of the Standard Model (NMSSM) with a Higgs boson of mass 125 GeV can be compatible with stop masses of order of the electroweak scale, thereby reducing the degree of finetuning necessary to achieve electroweak symmetry breaking. Moreover, in an attractive region of the NMSSM parameter space, corresponding to the "alignment limit" in which one of the neutral Higgs fields lies approximately in the same direction in field space as the doublet Higgs vacuum expectation value, the observed Higgs boson is predicted to have StandardModellike properties. We derive analytical expressions for the alignment conditions and show that they point toward a more natural region of parameter space for electroweak symmetry breaking, while allowing for perturbativity of the theory up to the Planck scale. Moreover, the alignment limit in the NMSSM leads to a well defined spectrum in the Higgs and Higgsino sectors, and yields a rich and interesting Higgs boson phenomenology that can be tested at the LHC. We discuss the most promising channels for discovery and present several benchmark points for further study. 
Article: Flavor from the Electroweak Scale
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ABSTRACT: We discuss the possibility that flavor hierarchies arise from the electroweak scale in a two Higgs doublet model, in which the two Higgs doublets jointly act as the flavon. Quark masses and mixing angles are explained by effective Yukawa couplings, generated by higher dimensional operators involving quarks and Higgs doublets. Modified Higgs couplings yield important effects on the production cross sections and decay rates of the light Standard Model like Higgs. In addition, flavor changing neutral currents arise at treelevel and lead to strong constraints from mesonantimeson mixing. Remarkably, flavor constraints turn out to prefer a region in parameter space that is in excellent agreement with the one preferred by recent Higgs precision measurements at the Large Hadron Collider (LHC). Direct searches for extra scalars at the LHC lead to further constraints. Precise predictions for the production and decay modes of the additional Higgs bosons are derived, and we present benchmark scenarios for searches at the LHC Run II. Flavor breaking at the electroweak scale as well as strong coupling effects demand a UV completion at the scale of a few TeV, possibly within the reach of the LHC. 
Dataset: 1410.4969

Article: Complementarity Between NonStandard Higgs Searches and Precision Higgs Measurements in the MSSM
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ABSTRACT: Precision measurements of the Higgs boson properties at the LHC provide relevant constraints on possible weakscale extensions of the Standard Model (SM). In the context of the Minimal Supersymmetric Standard Model (MSSM) these constraints seem to suggest that all the additional, nonSMlike Higgs bosons should be heavy, with masses larger than about 400 GeV. This article shows that such results do not hold when the theory approaches the conditions for "alignment independent of decoupling", where the lightest CPeven Higgs boson has SMlike treelevel couplings to fermions and gauge bosons, independently of the nonstandard Higgs boson masses. The combination of current bounds from direct Higgs boson searches at the LHC, along with the alignment conditions, have a significant impact on the allowed MSSM parameter space yielding light additional Higgs bosons. In particular, after ensuring the correct mass for the lightest CPeven Higgs boson, we find that precision measurements and direct searches are complementary, and may soon be able to probe the region of nonSMlike Higgs boson with masses below the top quark pair mass threshold of 350 GeV and low to moderate values of tanβ.  [Show abstract] [Hide abstract]
ABSTRACT: Warped extradimension models in which the Higgs boson is allowed to propagate in the bulk of a compact AdS5 space are conjectured to be dual to models featuring a partially composite Higgs boson. They offer a framework with which to investigate the implications of changing the scaling dimension of the Higgs operator, which can be used to reduce the constraints from electroweak precision data. In the context of such models, we calculate the cross section for Higgs production in gluon fusion and the H → γγ decay rate and show that they are finite (at oneloop order) as a consequence of gauge invariance. The extended scalar sector comprising the KaluzaKlein excitations of the Standard Model scalars is constructed in detail. The largest effects are due to virtual KK fermions, whose contributions to the cross section and decay rate introduce a quadratic sensitivity to the maximum allowed value y ∗ of the random complex entries of the 5D anarchic Yukawa matrices. We find an enhancement of the gluonfusion cross section and a reduction of the H →γγ rate as well as of the treelevel Higgs couplings to fermions and electroweak gauge bosons. We perform a detailed study of the correlated signal strengths for different production mechanisms and decay channels as functions of y ∗, the mass scale of KaluzaKlein resonances and the scaling dimension of the composite Higgs operator.  [Show abstract] [Hide abstract]
ABSTRACT: We study classically scale invariant models in which the Standard Model Higgs mass term is replaced in the Lagrangian by a Higgs portal coupling to a complex scalar field of a dark sector. We focus on models that are weakly coupled with the quartic scalar couplings nearly vanishing at the Planck scale. The dark sector contains fermions and scalars charged under dark SU(2) x U(1) gauge interactions. Radiative breaking of the dark gauge group triggers electroweak symmetry breaking through the Higgs portal coupling. Requiring both a Higgs boson mass of 125.5 GeV and stability of the Higgs potential up to the Planck scale implies that the radiative breaking of the dark gauge group occurs at the TeV scale. We present a particular model which features a longrange abelian dark force. The dominant dark matter component is neutral dark fermions, with the correct thermal relic abundance, and in reach of future direct detection experiments. The model also has lighter stable dark fermions charged under the dark force, with observable effects on galacticscale structure. Collider signatures include a dark sector scalar boson with mass < 250 GeV that decays through mixing with the Higgs boson, and can be detected at the LHC. The Higgs boson, as well as the new scalar, may have significant invisible decays into dark sector particles.  [Show abstract] [Hide abstract]
ABSTRACT: We consider composite Higgs models where the Higgs is a pseudoNambu Goldstone boson arising from the spontaneous breaking of an approximate global symmetry by some underlying strong dynamics. We focus on the SO(5) > SO(4) symmetry breaking pattern, assuming the partial compositeness paradigm. We study the consequences on Higgs physics of the fermionic representations produced by the strong dynamics, that mix with the Standard Model (SM) degrees of freedom. We consider models based on the lowestdimensional representations of SO(5) that allow for the custodial protection of the Z > b b coupling, i.e. the 5, 10 and 14. We find a generic suppression of the gluon fusion process, while the Higgs branching fractions can be enhanced or suppressed compared to the SM. Interestingly, a precise measurement of the Higgs boson couplings can distinguish between different realizations in the fermionic sector, thus providing crucial information about the nature of the UV dynamics.  [Show abstract] [Hide abstract]
ABSTRACT: In models with an extended Higgs sector there exists an alignment limit, in which the lightest CPeven Higgs boson mimics the Standard Model Higgs. The alignment limit is commonly associated with the decoupling limit, where all nonstandard scalars are significantly heavier than the $Z$ boson. However, alignment can occur irrespective of the mass scale of the rest of the Higgs sector. In this work we discuss the general conditions that lead to "alignment without decoupling", therefore allowing for the existence of additional nonstandard Higgs bosons at the weak scale. The values of $\tan\beta$ for which this happens are derived in terms of the effective Higgs quartic couplings in general twoHiggsdoublet models as well as in supersymmetric theories, including the MSSM and the NMSSM. Moreover, we study the information encoded in the variations of the SM Higgsfermion couplings to explore regions in the $m_A  \tan\beta$ parameter space.  [Show abstract] [Hide abstract]
ABSTRACT: We study extensions of the standard model by one generation of vectorlike leptons with nonstandard hypercharges, which allow for a sizable modification of the h > gamma gamma decay rate for new lepton masses in the 300 GeV  1 TeV range. We analyze vaccum stability implications for different hypercharges. Effects in h > Z gamma are typically much smaller than in h > gamma gamma, but distinct among the considered hypercharge assignments. Nonstandard hypercharges constrain or entirely forbid possible mixing operators with standard model leptons. As a consequence, the leading contributions to the experimentally strongly constrained electric dipole moments of standard model fermions are only generated at the two loop level by the new CP violating sources of the considered setups. We derive the bounds from dipole moments, electroweak precision observables and lepton flavor violating processes, and discuss their implications. Finally, we examine the production and decay channels of the vectorlike leptons at the LHC, and find that signatures with multiple light leptons or taus are already probing interesting regions of parameter space.  [Show abstract] [Hide abstract]
ABSTRACT: The ATLAS and CMS experiments have recently announced the discovery of a Higgslike resonance with mass close to 125 GeV. Overall, the data is consistent with a Standard Model (SM)like Higgs boson. Such a particle may arise in the minimal supersymmetric extension of the SM with average stop masses of the order of the TeV scale and a sizable stop mixing parameter. In this article we discuss properties of the SMlike Higgs production and decay rates induced by the possible presence of light staus and light stops. Light staus can affect the decay rate of the Higgs into diphotons and, in the case of sizable leftright mixing, induce an enhancement in this production channel up to ~ 50% of the Standard Model rate. Light stops may induce sizable modifications of the Higgs gluon fusion production rate and correlated modifications to the Higgs diphoton decay. Departures from SM values of the bottomquark and taulepton couplings to the Higgs can be obtained due to Higgs mixing effects triggered by light third generation scalar superpartners. We describe the phenomenological implications of light staus on searches for light stops and nonstandard Higgs bosons. Finally, we discuss the current status of the search for light staus produced in association with sneutrinos, in final states containing a W gauge boson and a pair of τ s. 
Article: Project X: Physics Opportunities
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ABSTRACT: Part 2 of "Project X: Accelerator Reference Design, Physics Opportunities, Broader Impacts". In this Part, we outline the particlephysics program that can be achieved with Project X, a staged superconducting linac for intensityfrontier particle physics. Topics include neutrino physics, kaon physics, muon physics, electric dipole moments, neutronantineutron oscillations, new light particles, hadron structure, hadron spectroscopy, and latticeQCD calculations. Part 1 is available as arXiv:1306.5022 [physics.accph] and Part 3 is available as arXiv:1306.5024 [physics.accph].  [Show abstract] [Hide abstract]
ABSTRACT: Current Higgs data at the Large Hadron Collider is compatible with a SM signal at the 2$\sigma$ level, but the central value of the signal strength in the diphoton channel is enhanced with respect to the SM expectation. If the enhancement resides in the diphoton partial decay width, the data could be accommodated in the Minimally Supersymmetric Standard Model (MSSM) with highly mixed light staus. We revisit the issue of vacuum instability induced by large mixing in the stau sector, including effects of a radiativelycorrected tau Yukawa coupling. Further, we emphasize the importance of taking into account the $\tan\beta$ dependence in the stability bound. While the metastability of the Universe constrains the possible enhancement in the Higgs to diphoton decay width in the light stau scenario, an increase of the order of 50% can be achieved in the region of large $\tan\beta$. Larger enhancements may be obtained, but would require values of $\tan\beta$ associated with nonperturbative values of the tau Yukawa coupling at scales below the GUT scale, thereby implying the presence of new physics beyond the MSSM.  [Show abstract] [Hide abstract]
ABSTRACT: We study the minimal supersymmetric standard model (MSSM) with minimal flavor violation (MFV), imposing constraints from flavor physics observables and MSSM Higgs searches, in light of the recent discovery of a 125 GeV Higgs boson by ATLAS and CMS. We analyze the electroweak vacuum stability conditions to further restrict the MSSM parameter space. In addition, a connection to ultraviolet physics is shown via an implementation of renormalization group running, which determines the TeVscale spectrum from a small set of minimal supergravity parameters. Finally, we investigate the impact from dark matter direct detection searches. Our work highlights the complementarity of collider, flavor and dark matter probes in exploring the MSSM, and shows that even in a MFV framework, flavor observables constrain the MSSM parameter space well beyond the current reach of direct SUSY particle searches.  [Show abstract] [Hide abstract]
ABSTRACT: Electroweak baryogenesis is an attractive scenario for the generation of the baryon asymmetry of the universe as its realization depends on the presence at the weak scale of new particles which may be searched for at high energy colliders. In the MSSM it may only be realized in the presence of light stops, and with moderate or small mixing between the left and righthanded components. Consistency with the observed Higgs mass around 125 GeV demands the heavier stop mass to be much larger than the weak scale. Moreover the lighter stop leads to an increase of the gluongluon fusion Higgs production cross section which seems to be in contradiction with indications from current LHC data. We show that this tension may be considerably relaxed in the presence of a light neutralino with a mass lower than about 60 GeV, satisfying all present experimental constraints. In such a case the Higgs may have a significant invisible decay width and the stop decays through a three or four body decay channel, including a bottom quark and the lightest neutralino in the final state. All these properties make this scenario testable at a high luminosity LHC.  [Show abstract] [Hide abstract]
ABSTRACT: Motivated by recent results from Higgs searches at the Large Hadron Collider, we consider possibilities to enhance the diphoton decay width of the Higgs boson over the Standard Model expectation, without modifying either its production rate or the partial widths in the WW and ZZ channels. Studying effects of new charged scalars, fermions and vector bosons, we find that significant variations in the diphoton width may be possible if the new particles have light masses of the order of a few hundred GeV and sizeable couplings to the Higgs boson. Such couplings could arise naturally if there is large mass mixing between two charged particles that is induced by the Higgs vacuum expectation value. In addition, there is generically also a shift in the Z + Gamma partial width, which in the case of new vector bosons tends to be of similar magnitude as the shift in the diphoton partial width, but smaller in other cases. Therefore simultaneous measurements in these two channels could reveal properties of new charged particles at the electroweak scale.  [Show abstract] [Hide abstract]
ABSTRACT: The LHC has started to constrain supersymmetrybreaking parameters by setting bounds on possible colored particles at the weak scale. Moreover, constraints from Higgs physics, flavor physics, the anomalous magnetic moment of the muon, as well as from searches at LEP and the Tevatron have set additional bounds on these parameters. Renormalization Group Invariants (RGIs) provide a very useful way of representing the allowed parameter space by making direct connection with the values of these parameters at the messenger scale. Using a general approach, based on the pMSSM parametrization of the soft supersymmetrybreaking parameters, we analyze the current experimental constraints to determine the probability distributions for the RGIs. As examples of their application, we use these distributions to analyze the question of Gaugino Mass Unification and to probabilistically determine the parameters of General and Minimal Gauge Mediation with arbitrary Higgs mass parameters at the Messenger Scale.  [Show abstract] [Hide abstract]
ABSTRACT: Recently, an excess of events consistent with a Higgs boson with mass of about 125 GeV was reported by the CMS and ATLAS experiments. This Higgs boson mass is consistent with the values that may be obtained in minimal supersymmetric extensions of the Standard Model (SM), with both stop masses less than a TeV and large mixing. The apparently enhanced photon production rate associated with this potential Higgs signal may be the result of light staus with large mixing. Large stau mixing and large coupling of the staus to the SMlike Higgs boson may be obtained for large values of tan β and moderate to large values of the Higgsino mass parameter, μ. We study the phenomenological properties of this scenario, including precision electroweak data, the muon anomalous magnetic moment, Dark Matter, and the evolution of the soft supersymmetrybreaking parameters to high energies. We also analyze the possible collider signatures of light third generation sleptons and demonstrate that it is possible to find evidence of their production at the 8 TeV and the 14 TeV LHC. The most promising channel is stau and tau sneutrino associated production, with the sneutrino decaying into a W boson plus a light stau.  [Show abstract] [Hide abstract]
ABSTRACT: Measurements of the Higgsboson production cross section at the LHC are an important tool for studying electroweak symmetry breaking at the quantum level, since the main production mechanism gg>h is loopsuppressed in the Standard Model (SM). Higgs production in extradimensional extensions of the SM is sensitive to the KaluzaKlein (KK) excitations of the quarks, which can be exchanged as virtual particles in the loop. In the context of the minimal RandallSundrum (RS) model with bulk fields and a branelocalized Higgs sector, we derive closed analytical expressions for the gluongluon fusion process, finding that the effect of the infinite tower of virtual KK states can be described in terms of a simple function of the fundamental (5D) Yukawa matrices. Given a specific RS model, this will allow one to easily constrain the parameter space, once a Higgs signal has been established. We explain that discrepancies between existing calculations of Higgs production in RS models are related to the noncommutativity of two limits: taking the number of KK states to infinity and removing the regulator on the Higgsboson profile, which is required in an intermediate step to make the relevant overlap integrals well defined. Even though the oneloop gg>h amplitude is finite in RS scenarios with a branelocalized Higgs sector, it is important to introduce a consistent ultraviolet regulator in order to obtain the correct result.  [Show abstract] [Hide abstract]
ABSTRACT: In a variety of well motivated models, such as two Higgs Doublet Models (2HDMs) and the Minimal Supersymmetric Standard Model (MSSM), there are neutral Higgs bosons that have significantly enhanced couplings to bquarks and tau leptons in comparison to those of the SM Higgs. These so called nonstandard Higgs bosons could be copiously produced at the LHC in association with b quarks, and subsequently decay into bquark pairs. However, this production channel suffers from large irreducible QCD backgrounds. We propose a new search strategy for nonstandard neutral Higgs bosons at the 7 TeV LHC in the 3b's final state topology. We perform a simulation of the signal and backgrounds, using state of the art tools and methods for different sets of selection cuts, and conclude that neutral Higgs bosons with couplings to bquarks of about 0.3 or larger, and masses up to 400 GeV, could be seen with a luminosity of 30 fb^{1}. In the case of the MSSM we also discuss the complementarity between the 3b channel and the inclusive tau pair channel in exploring the supersymmetric parameter space.
Publication Stats
4k  Citations  
292.42  Total Impact Points  
Top Journals
Institutions

20082015

University of Chicago
 • Enrico Fermi Institute
 • Department of Physics
Chicago, Illinois, United States


20022012

Fermi National Accelerator Laboratory (Fermilab)
 Theoretical Physics Department
Батавия, Illinois, United States


2000

CERN
 Physics Department (PH)
Genève, Geneva, Switzerland
