"Long before it's in the papers"
January 27, 2015


Higgs boson could explain facets of “dark energy,” physicists say

Aug. 12, 2013
Courtesy of 
and World Science staff

One of the big­gest mys­ter­ies in phys­ics is why a mys­te­ri­ous sub­stance called “dark en­er­gy,” found to dom­i­nate the en­er­gy count in the uni­verse, has a smaller val­ue than it’s sup­posed to have.

Sci­en­tists es­ti­mate that val­ue as one-followed-by-120-zeros times smaller than would be ex­pected based on fun­da­men­tal phys­ics. The puz­zle is of­ten called the cos­mo­lo­g­i­cal con­stant prob­lem.

Now, two phys­i­cists sug­gest that the re­cently dis­cov­ered Higgs bos­on—an ent­ity con­sid­ered re­spon­si­ble for giv­ing ob­jects their mass, so they can weigh some­thing—is al­so be­hind the cos­mo­lo­g­i­cal con­stant prob­lem. 

The sci­en­tists, Law­rence Krauss of Ar­i­zo­na State Uni­vers­ity and James Dent of the Uni­vers­ity of Louisiana-Lafayette, say the bos­on could pro­vide a pos­si­ble “por­tal” to phys­ics that could help ex­plain some of the at­tributes of the en­ig­mat­ic dark en­er­gy. The Higgs, they ex­plain, might achieve this by in­ter­act­ing with oth­er par­t­i­cles whose ex­ist­ence is pre­dicted, though not yet dis­cov­ered—as the Higgs it­self was not long ago.

Dur­ing a time when the uni­verse was ex­tremely small and hot, these par­t­i­cles could lead to the ex­ist­ence of a back­ground “field” in na­ture in ad­di­tion to the Higgs, which is al­so has prop­er­ties of a field. A field is a quantity that has a val­ue for each point in space and time. This sec­ond field would con­trib­ute an “en­er­gy dens­ity” to emp­ty space of pre­cisely the cor­rect scale, they added. En­er­gy dens­ity is the amount of en­er­gy per giv­en space.

Krauss and Dent pub­lished find­ings on­line, Aug. 9, in the jour­nal Phys­i­cal Re­view Let­ters.

Ob­serva­t­ions show the uni­verse is ex­pand­ing ev­er faster. To help ex­plain this, sci­en­tists in­fer the ex­ist­ence of this as-yet-undefined “dark en­er­gy,” which con­trib­utes up to 70 pe­rcent of the en­er­gy dens­ity in the uni­verse. Ob­servable mat­ter con­trib­utes only an es­ti­mated 2 to 5 pe­rcent of this en­er­gy, with the re­main­ing 25 pe­rcent or so com­ing from a “dark mat­ter.”

The source of this dark en­er­gy and the rea­son cal­cula­t­ions keep throw­ing up a too-high val­ue for it makes it one of the lead­ing out­stand­ing prob­lems in par­t­i­cle phys­ics.

“Our pape­r makes prog­ress in one as­pect of this prob­lem,” said Krauss. “Now that the Higgs bos­on has been dis­cov­ered, it pro­vides a pos­si­ble ‘por­tal’ to phys­ics at much high­er en­er­gy scales,” he added. “Our pape­r demon­strates that a very small en­er­gy scale can at least be nat­u­rally gen­er­at­ed with­in the con­text of a very sim­ple ex­ten­sion of the stand­ard mod­el of par­t­i­cle phys­ics.”

But “the deepe­r prob­lem of why the known phys­ics of the stand­ard mod­el does not con­trib­ute a much larg­er en­er­gy to emp­ty space is still not re­solved,” he said.

* * *

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One of the biggest mysteries in physics is why a mysterious substance called “dark energy,” found to dominate the energy count in the universe, has a smaller value than it’s supposed to have. The value is so small, scientists estimate it as one-followed-by-120-zeros times smaller than would be expected based on fundamental physics. The puzzle is often called the cosmological constant problem. Now, two physicists suggest that the recently discovered Higgs boson—an entity considered responsible for giving objects their mass, so they can weigh something—is also behind the cosmological constant problem. The scientists, Lawrence Krauss of Arizona State University and James Dent of the University of Louisiana-Lafayette, say the boson could provide a possible “portal” to physics that could help explain some of the attributes of the enigmatic dark energy. The Higgs, they explain, might achieve this by interacting with other particles whose existence is predicted, though not yet discovered—as the Higgs itself was not long ago. During a time when the universe was extremely small and hot, these particles could lead to the existence of a background “field” in nature in addition to the Higgs, which is also has properties of a field. A field is a quantity that has a value for each point in space and time. This second field would contribute an “energy density” to empty space of precisely the correct scale, they added. Energy density is the amount of energy per given space. Krauss and Dent published findings online, Aug. 9, in the journal Physical Review Letters. Observations show the universe is expanding ever faster. To help explain this, scientists infer the existence of this as-yet-undefined “dark energy,” which contributes up to 70 percent of the energy density in the universe. Observable matter contributes only an estimated 2 to 5 percent of this energy, with the remaining 25 percent or so coming from a “dark matter.” The source of this dark energy and the reason calculations keep throwing up a too-high value for it makes it one of the leading outstanding problems in particle physics. “Our paper makes progress in one aspect of this problem,” said Krauss. “Now that the Higgs boson has been discovered, it provides a possible ‘portal’ to physics at much higher energy scales,” he added. “Our paper demonstrates that a very small energy scale can at least be naturally generated within the context of a very simple extension of the standard model of particle physics.” But “the deeper problem of why the known physics of the standard model does not contribute a much larger energy to empty space is still not resolved,” he said.