Santa Cruz Institute for Particle Physics

Saint Helena, CA, United States

Santa Cruz Institute for Particle Physics

Saint Helena, CA, United States

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Bernon J.,CNRS Laboratory of Subatomic Physics & Cosmology | Gunion J.F.,University of California at Davis | Haber H.E.,Santa Cruz Institute for Particle Physics | Jiang Y.,University of California at Davis | Kraml S.,CNRS Laboratory of Subatomic Physics & Cosmology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

In the alignment limit of a multidoublet Higgs sector, one of the Higgs mass eigenstates aligns with the direction of the scalar field vacuum expectation values, and its couplings approach those of the Standard Model (SM) Higgs boson. We consider CP-conserving two-Higgs-doublet models (2HDMs) of Type I and Type II near the alignment limit in which the lighter of the two CP-even Higgs bosons, h, is the SM-like state observed at 125 GeV. In particular, we focus on the 2HDM parameter regime where the coupling of h to gauge bosons approaches that of the SM. We review the theoretical structure and analyze the phenomenological implications of the regime of the alignment limit without decoupling, in which the other Higgs scalar masses are not significantly larger than mh and thus do not decouple from the effective theory at the electroweak scale. For the numerical analysis, we perform scans of the 2HDM parameter space employing the software packages 2hdmc and lilith, taking into account all relevant pre-LHC constraints, the latest constraints from the measurements of the 125 GeV Higgs signal at the LHC, as well as the most recent limits coming from searches for heavy Higgs-like states. We contrast these results with the alignment limit achieved via the decoupling of heavier scalar states, where h is the only light Higgs scalar. Implications for Run 2 at the LHC, including expectations for observing the other scalar states, are also discussed. © 2015 American Physical Society. © 2015 American Physical Society.

D'Eramo F.,University of California at Santa Cruz | D'Eramo F.,Santa Cruz Institute for Particle Physics | de Vries J.,Theory Group | Panci P.,University Pierre and Marie Curie
Journal of High Energy Physics | Year: 2016

Abstract: We study the effective field theory obtained by extending the Standard Model field content with two singlets: a 750 GeV (pseudo-)scalar and a stable fermion. Accounting for collider productions initiated by both gluon and photon fusion, we investigate where the theory is consistent with both the LHC diphoton excess and bounds from Run 1. We analyze dark matter phenomenology in such regions, including relic density constraints as well as collider, direct, and indirect bounds. Scalar portal dark matter models are very close to limits from direct detection and mono-jet searches if gluon fusion dominates, and not constrained at all otherwise. Pseudo-scalar models are challenged by photon line limits and mono-jet searches in most of the parameter space. © 2016, The Author(s).

Boucenna M.S.,University of Valencia | Boucenna M.S.,University of California at Santa Cruz | Profumo S.,University of California at Santa Cruz | Profumo S.,Santa Cruz Institute for Particle Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

A recent study of gamma-ray data from the Galactic center motivates the investigation of light (∼7-10GeV) particle dark matter models featuring tau-lepton pairs as dominant annihilation final state. The lepton-specific two-Higgs-doublet model provides a natural framework where light, singlet scalar dark matter can pair-annihilate dominantly into tau leptons. We calculate the nucleon-dark matter cross section for singlet scalar dark matter within the lepton-specific two-Higgs-doublet model framework, and compare with recent results from direct detection experiments. We study how direct dark matter searches can be used to constrain the dark matter interpretation of gamma-ray observations, for different dominant annihilation final states. We show that models exist with the correct thermal relic abundance that could fit the claimed gamma-ray excess from the Galactic center region and have direct detection cross sections of the order of what is needed to interpret recent anomalous events reported by direct detection experiments. © 2011 American Physical Society.

Feng J.L.,University of California at Irvine | Kant P.,Humboldt University of Berlin | Profumo S.,University of California at Santa Cruz | Profumo S.,Santa Cruz Institute for Particle Physics | Sanford D.,California Institute of Technology
Physical Review Letters | Year: 2013

In supersymmetric models with minimal particle content and without left-right squark mixing, the conventional wisdom is that the 125.6 GeV Higgs boson mass implies top squark masses of O(10) TeV, far beyond the reach of colliders. This conclusion is subject to significant theoretical uncertainties, however, and we provide evidence that it may be far too pessimistic. We evaluate the Higgs boson mass, including the dominant three-loop terms at O(αtαs2), in currently viable models. For multi-TeV top squarks, the three-loop corrections can increase the Higgs boson mass by as much as 3 GeV and lower the required top-squark masses to 3-4 TeV, greatly improving prospects for supersymmetry discovery at the upcoming run of the LHC and its high-luminosity upgrade. © 2013 American Physical Society.

Draper P.,Santa Cruz Institute for Particle Physics | Lee G.,University of Chicago | Wagner C.E.M.,University of Chicago | Wagner C.E.M.,Argonne National Laboratory
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

In supersymmetric models, very heavy stop squarks introduce large logarithms into the computation of the Higgs boson mass. Although it has long been known that in simple cases these logs can be resummed using effective field theory techniques, it is technically easier to use fixed-order formulas, and many public codes implement the latter. We calculate three- and four-loop next-to-next-to-leading-log corrections to the Higgs mass and compare the fixed-order formulas numerically to the resummation results in order to estimate the range of supersymmetry scales where the fixed-order results are reliable. We find that the four-loop result may be accurate up to a few tens of TeV. We confirm an accidental cancellation between different three-loop terms, first observed in S.P. Martin, Phys. Rev. D 75, 055005 (2007), and show that it persists to higher scales and becomes more effective with the inclusion of higher radiative corrections. Existing partial three-loop calculations that include only one of the two cancelling terms may overestimate the Higgs mass. We give analytic expressions for the three- and four-loop corrections in terms of Standard Model parameters and provide a complete dictionary for translating parameters between the SM and the MSSM and the MS̄ and DR̄ renormalization schemes. © 2014 American Physical Society.

Hallman E.J.,Harvard - Smithsonian Center for Astrophysics | Jeltema T.E.,Santa Cruz Institute for Particle Physics
Monthly Notices of the Royal Astronomical Society | Year: 2011

We track the histories of massive clusters of galaxies formed within a cosmological hydrodynamic simulation. Specifically, we track the time evolution of the energy in random bulk motions of the intracluster medium and X-ray measures of cluster structure and their relationship to cluster mergers. We aim to assess the viability of the turbulent re-acceleration model for the generation of giant radio haloes by comparing the level of turbulent kinetic energy in simulated clusters with the observed properties of radio halo clusters, giving particular attention to the association of radio haloes to clusters with disturbed X-ray structures. The evolution of X-ray cluster structure and turbulence kinetic energy, k, in simulations can then inform us about the expected lifetime of radio haloes and the fraction of clusters as a function of redshift expected to host them. We find strong statistical correlation of disturbed structure measures and the presence of enhancements in k. Specifically, quantitatively 'disturbed', radio halo-like X-ray morphology in our sample indicates a 92 per cent chance of the cluster in question having k elevated to more than twice its minimum value over the cluster's life. The typical lifetime of episodes of elevated turbulence is on the order of 1 Gyr, though these periods can last 5Gyr or more. This variation reflects the wide range of cluster histories; while some clusters undergo complex and repeated mergers spending a majority of their time in elevated k states, other clusters are relaxed over nearly their entire history. We do not find a bimodal relationship between cluster X-ray luminosity and the total energy in turbulence that might account directly for a bimodal LX-P1.4GHz relation. However, our result may be consistent with the observed bimodality, as here we are not including a full treatment of cosmic ray sources and magnetic fields. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Aguirre A.,University of California at Santa Cruz | Aguirre A.,Santa Cruz Institute for Particle Physics | Kozaczuk J.,University of California at Santa Cruz
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

Collisions between cosmic bubbles of different vacua are a generic feature of false vacuum eternal inflation scenarios. While previous studies have focused on the consequences of a single collision event in an observer's past, we begin here an investigation of the more general scenario allowing for many "mild" collisions intersecting our past light cone (and one another). We discuss the general features of multiple collision scenarios and consider their impact on the cosmic microwave background (CMB) temperature power spectrum, treating the collisions perturbatively. In a large class of models, one can approximate a multiple collision scenario as a superposition of individual collision events governed by nearly isotropic and scale-invariant distributions, most appearing to take up less than half of the sky. In this case, the shape of the expected CMB temperature spectrum maintains statistical isotropy and typically features a dramatic increase in power in the low multipoles relative to that of the best-fit ΛCDM model, which is in tension particularly with the observed quadrupole. We argue that this predicted spectrum is largely model independent and can be used to outline features of the underlying statistical distributions of colliding bubbles consistent with CMB temperature measurements. © 2013 American Physical Society.

Profumo S.,University of California at Santa Cruz | Profumo S.,Santa Cruz Institute for Particle Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

We compare the first results on searches for supersymmetry with the Large Hadron Collider (LHC) to the current and near-term performance of experiments sensitive to neutralino dark matter. We limit our study to the particular slices of parameter space of the constrained minimal supersymmetric extension to the standard model where CMS and ATLAS exclusion limits have been presented so far. We show where, on that parameter space, the lightest neutralino possesses a thermal relic abundance matching the value inferred by cosmological observations. We then calculate rates for, and estimate the performance of, experiments sensitive to direct and indirect signals from neutralino dark matter. We argue that this is a unique point in time, where the quest for supersymmetry-at least in one of its practical and simple incarnations-is undergoing a close scrutiny from the LHC and from dark matter searches that is both synergistic and complementary. Should the time of discovery finally unravel, the current performances of the collider program and of direct and indirect dark matter searches are at a conjuncture offering unique opportunities for a breakthrough on the nature of physics beyond the standard model. © 2011 American Physical Society.

Wainwright C.,University of California at Santa Cruz | Profumo S.,University of California at Santa Cruz | Profumo S.,Santa Cruz Institute for Particle Physics | Ramsey-Musolf M.J.,University of Wisconsin - Madison
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

The finite-temperature effective potential customarily employed to describe the physics of cosmological phase transitions often relies on specific gauge choices, and is manifestly not gauge invariant at finite order in its perturbative expansion. As a result, quantities relevant for the calculation of the spectrum of stochastic gravity waves resulting from bubble collisions in first-order phase transitions are also not gauge invariant. We assess the quantitative impact of this gauge dependence on key quantities entering predictions for gravity waves from first-order cosmological phase transitions. We resort to a simple Abelian Higgs model, and discuss the case of R ξ gauges. By comparing with results obtained using a gauge-invariant Hamiltonian formalism, we show that the choice of gauge can have a dramatic effect on theoretical predictions for the normalization and shape of the expected gravity wave spectrum. We also analyze the impact of resumming higher-order contributions as needed to maintain the validity of the perturbative expansion, and show that doing so can suppress the amplitude of the spectrum by an order of magnitude or more. We comment on open issues and possible strategies for carrying out "daisy resummed" gauge-invariant computations in non-Abelian models for which a gauge-invariant Hamiltonian formalism is not presently available. © 2011 American Physical Society.

Kozaczuk J.,University of California at Santa Cruz | Profumo S.,University of California at Santa Cruz | Profumo S.,Santa Cruz Institute for Particle Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

Recent results from the cryogenic dark matter search experiment have renewed interest in light (5-15 GeV) dark matter with a large spin-independent neutralino-nucleon scattering cross section, σSI10-42cm2. Previous work had suggested that the lightest neutralino in the next-to-MSSM can fall in this mass range and achieve both the correct thermal relic abundance and the desired level for the scattering cross section, provided light Higgs bosons to mediate the pair annihilation and neutralino-nucleon scattering. However, the requirement of a 126 GeV standard model (SM)-like Higgs boson significantly impacts the allowed parameter space. Here, we examine the regions of the NMSSM capable of producing a light neutralino with σSI∼10-42-10-41cm2, with the scattering mediated by a very light singlet-like scalar, and a 126 GeV standard model-like Higgs consistent with the LHC results, while satisfying other relevant cosmological, flavor and collider constraints. We focus on two different scenarios for annihilation in the early Universe, namely annihilation mediated by (1) a light scalar or by (2) a light pseudoscalar. As expected, both cases are highly constrained. Nevertheless, we find that there persists potentially viable parameter space to accommodate either scenario. In the first, accidental cancellations in the couplings allow for a SM-like Higgs with a total width and invisible branching fraction compatible with the observed Higgs boson. Alternatively, the second scenario can occur in regions featuring smaller branching fractions of the SM-like Higgs to pairs of light scalars, pseudoscalars, and neutralinos without cancellations. The strongest constraints in both cases come from rare meson decays and exotic decays of the SM-like Higgs boson into neutralinos and light, charge parity even Higgs pairs. We outline the relevant parameter space for both scenarios and comment on prospects for future discovery with various experiments. © 2014 American Physical Society.

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