Recursos de colección

Caltech Authors (143.226 recursos)

Repository of works by Caltech published authors.

Group = Caltech Theory

Mostrando recursos 1 - 20 de 262

  1. Dark matter is real

    Carroll, Sean
    The combined data from four systems of telescopes offer the strongest evidence yet that a modification of gravity cannot do away with the need for dark matter.

  2. In What Sense Is the Early Universe Fine-Tuned?

    Carroll, Sean M.
    It is commonplace in discussions of modern cosmology to assert that the early universe began in a special state. Conventionally, cosmologists characterize this fine-tuning in terms of the horizon and flatness problems. I argue that the fine-tuning is real, but these problems aren't the best way to think about it: causal disconnection of separated regions isn't the real problem, and flatness isn't a problem at all. Fine-tuning is better understood in terms of a measure on the space of trajectories: given reasonable conditions in the late universe, the fraction of cosmological histories that were smooth at early times is incredibly tiny. This discussion helps clarify what is required...

  3. Electroweak baryogenesis, electric dipole moments, and Higgs diphoton decays

    Chao, Wei; Ramsey-Musolf, Michael J.
    We study the viability of electroweak baryogenesis in a two Higgs doublet model scenario augmented by vector-like, electroweakly interacting fermions. Considering a limited, but illustrative region of the model parameter space, we obtain the observed cosmic baryon asymmetry while satisfying present constraints from the non-observation of the permanent electric dipole moment (EDM) of the electron and the combined ATLAS and CMS result for the Higgs boson diphoton decay rate. The observation of a non-zero electron EDM in a next generation experiment and/or the observation of an excess (over the Standard Model) of Higgs to diphoton events with the 14 TeV...

  4. Membrane quantum mechanics

    Okazaki, Tadashi
    We consider the multiple M2-branes wrapped on a compact Riemann surface and study the arising quantum mechanics by taking the limit where the size of the Riemann surface goes to zero. The IR quantum mechanical models resulting from the BLG-model and the ABJM-model compactified on a torus are N=16 and N=12 superconformal gauged quantum mechanics. After integrating out the auxiliary gauge fields we find OSp(16|2) and SU(1,1|6) quantum mechanics from the reduced systems. The curved Riemann surface is taken as a holomorphic curve in a Calabi–Yau space to preserve supersymmetry and we present a prescription of the topological twisting. We...

  5. Covariant constraints for generic massive gravity and analysis of its characteristics

    Deser, S.; Sandora, M.; Waldron, A.; Zahariade, G.
    We perform a covariant constraint analysis of massive gravity valid for its entire parameter space, demonstrating that the model generically propagates 5 degrees of freedom; this is also verified by a new and streamlined Hamiltonian description. The constraint’s covariant expression permits computation of the model’s caustics. Although new features such as the dynamical Riemann tensor appear in the characteristic matrix, the model still exhibits the pathologies uncovered in earlier work: superluminality and likely acausalities.

  6. BPS Soliton Solutions of a D3-brane Action

    Schwarz, John H.
    The world-volume action of a probe D3-brane in AdS_5 X S^5 with N = 4 units of flux has the field content, symmetries, and dualities of the U(1) factor of N = 4U(N+1) super Yang--Mills theory, spontaneously broken to U(N) x U(1) by being on the Coulomb branch, with the massive fields integrated out. Thus, it might be the exact effective action (a highly effective action), or else a useful approximation to it. We construct an SL(2,Z) multiplet of BPS soliton solutions of the D3-brane action and show that in the N = 1 case they correspond to the electrically charged states that have been integrated out as...

  7. Banjo timbre from string stretching and frequency modulation

    Politzer, David
    The geometry of a floating bridge on a drumhead soundboard produces string stretching that is first order in the amplitude of the bridge motion. This stretching modulates the string tension and consequently modulates string frequencies at acoustic frequencies. Early work in electronic sound synthesis identified such modulation as a source of bell-like and metallic timbre. And increasing string stretching by adjusting banjo string-tailpiece-head geometry enhances characteristic banjo tone. Hence, this mechanism is likely a significant source of the ring, ping, clang, and plunk common to the family of instruments that share floating-bridge/drumhead construction.

  8. The plucked string: An example of non-normal dynamics

    Politzer, David
    The motion of a single Fourier mode of the plucked string is an example of transient, free decay of linear, coupled, damped oscillators. It shares the rarely discussed features of the generic case, e.g., possessing a complete set of non-orthogonal eigenvectors and no normal modes, but it can be analyzed and solved analytically by hand in an approximation that is appropriate to musical instruments' plucked strings.

  9. Disrupting Entanglement of Black Holes

    Leichenauer, Stefan
    We study entanglement in thermofield double states of strongly coupled conformal field theories by analyzing two-sided Reissner-Nordström solutions in anti–de Sitter space. The central object of study is the mutual information between a pair of regions, one on each asymptotic boundary of the black hole. For large regions the mutual information is positive and for small ones it vanishes; we compute the critical length scale, which goes to infinity for extremal black holes, of the transition. We also generalize the butterfly effect of Shenker and Stanford [J. High Energy Phys. 03 (2014) 067] to a wide class of charged black...

  10. Unconstrained canonical action for, and positive energy of, massive spin 2

    Deser, S.
    Filling a much-needed gap, we exhibit the D = 4 Fierz–Pauli massive s = 2 action, and its — manifestly positive — energy, in terms of its 2s + 1 = 5 unconstrained helicity (2, 1, 0) excitations, after reducing and diagonalizing the troublesome helicity-zero sector.

  11. Gauge Theories on the Coulomb branch

    Schwarz, John H.
    We construct the world-volume action of a probe D3-brane in AdS_5×S^5 with N units of flux. It has the field content, symmetries, and dualities of the U(1) factor of N = 4 U(N + 1) super Yang–Mills theory, spontaneously broken to U(N)×U(1) by being on the Coulomb branch, with the massive fields integrated out. This motivates the conjecture that it is the exact effective action, called a highly effective action (HEA). We construct an SL(2,ℤ) multiplet of BPS soliton solutions of the D3-brane theory (the conjectured HEA) and show that they reproduce the electrically charged massive states that have been integrated out as well as magnetic monopoles and...

  12. Infrared Consistency and the Weak Gravity Conjecture

    Cheung, Clifford; Remmen, Grant N.
    The weak gravity conjecture (WGC) asserts that an Abelian gauge theory coupled to gravity is inconsistent unless it contains a particle of charge q and mass m such that q≥m/m_(Pl). This criterion is obeyed by all known ultraviolet completions and is needed to evade pathologies from stable black hole remnants. In this paper, we explore the WGC from the perspective of low-energy effective field theory. Below the charged particle threshold, the effective action describes a photon and graviton interacting via higher-dimension operators. We derive infrared consistency conditions on the parameters of the effective action using i ) analyticity of light-by-light...

  13. CP-violating phenomenology of flavor conserving two Higgs doublet models

    Inoue, Satoru; Ramsey-Musolf, Michael J.; Zhang, Yue
    We analyze the constraints on CP-violating, flavor conserving two Higgs doublet models implied by measurements of Higgs boson properties at the Large Hadron Collider (LHC) and by the nonobservation of permanent electric dipole moments (EDMs) of molecules, atoms, and neutrons. We find that the LHC and EDM constraints are largely complementary, with the LHC studies constraining the mixing between the neutral CP-even states and the EDMs probing the effect of mixing between the CP-even and CP-odd scalars. Presently, the most stringent constraints are implied by the nonobservation of the ThO molecule EDM signal. Future improvements in the sensitivity of neutron...

  14. Stable Bound States of Asymmetric Dark Matter

    Wise, Mark B.; Zhang, Yue
    The simplest renormalizable effective field theories with asymmetric dark matter bound states contain two additional gauge singlet fields, one being the dark matter and the other a mediator particle that the dark matter annihilates into. We examine the physics of one such model with a Dirac fermion as the dark matter and a real scalar mediator. For a range of parameters the Yukawa coupling of the dark matter to the mediator gives rise to stable asymmetric dark matter bound states. We derive properties of the bound states including nuggets formed from N ≫ 1 dark matter particles. We also consider the formation of bound states...

  15. NMSSM Interpretation of the Galactic Center Excess

    Cheung, Clifford; Papucci, Michele; Sanford, David; Shah, Nausheen R.; Zurek, Kathryn M.
    We explore models for the GeV Galactic Center Excess (GCE) observed by the Fermi Telescope, focusing on χχ→ƒƒ(bar) annihilation processes in the Z3 NMSSM. We begin by examining the requirements for a simplified model (parametrized by the couplings and masses of dark matter (DM) and mediator particles) to reproduce the GCE via χχ→ƒƒ^bar, while simultaneously thermally producing the observed relic abundance. We apply the results of our simplified model to the Z_3 NMSSM for Singlino/Higgsino~(S/H) or Bino/Higgsino~(B/H) DM. In the case of S/H DM, we find that the DM must be be very close to a pseudoscalar resonance to be...

  16. Anomalous Discrete Symmetries in Three Dimensions and Group Cohomology

    Kapustin, Anton; Thorngren, Ryan
    We study ’t Hooft anomalies for a global discrete internal symmetry G . We construct examples of bosonic field theories in three dimensions with a nonvanishing ’t Hooft anomaly for a discrete global symmetry. We also construct field theories in three dimensions with a global discrete internal symmetry G_1×G_2 such that gauging G_1 necessarily breaks G_2 and vice versa. This is analogous to the Adler-Bell-Jackiw axial anomaly in four dimensions and parity anomaly in three dimensions.

  17. Probing the Higgs portal at the LHC through resonant di-Higgs production

    No, Jose M.; Ramsey-Musolf, Michael J.
    We investigate resonant di-Higgs production as a means of probing extended scalar sectors that include a 125 GeV Standard Model-like Higgs boson. For concreteness, we consider a gauge singlet Higgs portal scenario leading to two mixed doublet-singlet states, h_(1,2). For m(_h_2)>2m(_h_1), the resonant di-Higgs production process pp→h_(2)→h_(1)h_(1) will lead to final states associated with the decaying pair of Standard Model-like Higgs scalars. We focus on h_(2) production via gluon fusion and on the bb^¯τ^(+)τ^(−) final state. We find that discovery of the h_(2) at the LHC may be achieved with ≲100  fb^(−1) of integrated luminosity for benchmark parameter choices relevant to...

  18. Improvement of energy-momentum tensor and non-Gaussianities in holographic cosmology

    Kawai, Shinsuke; Nakayama, Yu
    In holographic models of cosmology based on the (A)dS/CFT correspondence, conformal symmetry is implicit in the dual description of the Universe. Generically, however, one cannot expect the (broken) conformal invariance in the cosmic fluctuations as only the scale invariance is manifest in experiments. Also, in order for the prediction of the holographic models to make sense, the conformal symmetry needs to be broken as the scalar mode of the metric fluctuations becomes pure gauge in the conformal limit. We discuss the improvement ambiguity of the energy-momentum tensor in this context and construct a holographic model of the Universe that preserves...

  19. Seesaw theories at LHC and warm dark matter

    Zhang, Yue
    Explaining the origin of neutrino masses clearly requires new physics beyond the Standard Model. I focus on the Seesaw paradigm and discuss a few simplest extensions of the SM that give Majorana masses to the active neutrinos. If realized at TeV scale, seesaw theories could manifest themselves in lepton number violating signatures at both low-energy processes and high-energy collider experiments. I summarize the constraints on the seesaw scales using the current LHC data. The left-right symmetric model connects the seesaw mechanism with the origin of parity symmetry breaking, and provides a unified framework for the simplest seesaw types. With new...

  20. Xenophobic Dark Matter

    Sanford, David
    We describe models in which dark matter is xenophobic, with significantly reduced signal strength in direct detection experiments using xenon as a target material. Such models alleviate tension between xenon-based constraints and possible signal at other direct detection experiments, and in particular regions of interest at CoGeNT and CDMS are largely below XENON100 bounds in the purely xenophobic limit. We also show the constraints from upcoming LUX results and orthogonal searches using Fermi-LAT results from line searches in dwarf spheroidals and monojet searches at CMS.

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